JP2017024931A - Apatite type lanthanum silicate precursor thin film, manufacturing method therefor and apatite type lanthanum silicate thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apatite type lanthanum silicate precursor thin film capable of being used for efficiently manufacturing lanthanum silicate thin film having an apatite type crystal structure and sufficiently high in c axis orientation property.SOLUTION: There is provided an apatite type lanthanum silicate precursor consisting of a thin film which consists of an aggregate of composite oxide particles containing lanthanum and silicon as main metal elements, has volume fraction of gaps of fine pores with fine pore diameter of 16 nm or more of 1% or less based on total volume of the thin film, where the composite oxide particles consist of amorphous oxide and the composite oxide particles containing lanthanum and silicon are precipitated by heating a raw material solution containing a salt of lanthanum and alkoxysilane with ratio of lanthanum and silicate (La:Si) of 4:3 to 5:3 and having pH of 3.5 to 7 under a temperature condition of 350 to 600°C.SELECTED DRAWING: None

Description

  The present invention relates to an apatite-type lanthanum silicate precursor thin film, a method for producing the same, and an apatite-type lanthanum silicate thin film.

  Conventionally, composite metal oxides having an apatite-type crystal structure and c-axis orientation have been studied for use in oxygen sensors, solid oxide fuel cells, etc. as oxide ion conductors and the like. .

  Various methods are known as a method for producing a composite metal oxide having such an apatite-type crystal structure and having c-axis orientation, for example, Japanese Patent Application Laid-Open No. 2003-267800 (Patent Document 1). In Re, M is a molar ratio of Re: M (where Re represents at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy, and M represents at least one of Si and Ge). After forming an oxide powder having a composition of 8.00 to 11.00: 6.00, the obtained molded body or a sintered body thereof is heat-treated at 1000 to 1900 ° C. to grow crystals, thereby forming a composite. A method for producing a metal oxide is disclosed.

In Japanese Patent Application Laid-Open No. 2004-244282 (Patent Document 2), a powder of a substance having element A and oxygen O as constituent elements, and a powder of a substance having element B and oxygen O as constituent elements are described as A _X B ₆ O _{1.5X + 12} (where 8 ≦ X ≦ 10) is mixed to obtain a mixed powder, and the mixed powder is subjected to heat treatment to cause the mixed powder to react with the composition formula A A step of forming a composite oxide represented by _X B ₆ O _{1.5X + 12} (where 8 ≦ X ≦ 10), and adding the composite oxide to a solvent to form a slurry; then, the slurry in the presence of a magnetic field There is disclosed a method for producing a composite metal oxide, comprising a step of solidifying a compact to form a compact and a step of obtaining a composite oxide by sintering the compact.

  Further, in Japanese Patent Application Laid-Open No. 2011-037662 (Patent Document 3), an oxide raw material mixing step of mixing an oxide raw material containing a lanthanoid oxide powder and at least one oxide powder of Si or Ge, and mixing The molten oxide raw material is melted by heating to a liquid state, casted, and then rapidly cooled to obtain a glassy material, and the glassy material is heat-treated at 800 to 1400 ° C. for crystallization. A method for producing a composite metal oxide having a crystallization step is disclosed.

Furthermore, in JP2013-064194 (Patent Document 4), a trivalent A element, a tetravalent B element, and oxygen O are contained, and the composition formula is A _x B ₆ O _{1.5X + 12} ( However, in the method for producing a composite metal oxide represented by 6 ≦ X ≦ 30), after supplying the first raw material containing either the A element or the B element onto the substrate, oxidation is performed. A first film made of an oxide of either the A element or the B element is formed by supplying an agent, and then a second raw material containing one of the B element or the remaining A element is supplied. Then, the first film is formed by repeating the first process and the first process of forming a second film made of an oxide of either the B element or the A element by supplying an oxidizing agent. And a second layer obtained by laminating a plurality of the second films. Yes and step, subjected to a heat treatment to the substrate and the _{laminate, A x B 6 O 1.5X +} 12 ( although, 6 ≦ X ≦ 30) and a third step of forming a composite metal oxide film made of And a composite metal oxide that controls a composition ratio of the A element and the B element in the composite metal oxide film according to a ratio of the number of times of supply of the first raw material and the second raw material in the first step. As a specific method, a method using a so-called atomic layer deposition (ALD) apparatus (atomic layer deposition (ALD) method) is described.

Also published in Journal of Alloys and Compounds, Vol. 408-412, pages 641 to 644, “Preparation of apatite-type La _9.33 (SiO ₄ ) ₆ O ₂ oxide ion conductor-hydride lysis (non-patent document 1)”. Is disclosed in which a solution of lanthanum silicate is obtained by adding tetraethoxysilane (TEOS) to the solution after the solution is dissolved in nitric acid, refluxing the obtained solution, applying the solution on the substrate to the substrate and baking the solution. ing. In addition, it is clear that the pH of the solution described in Non-Patent Document 1 (solution before reflux) is less than 1 due to the amount of nitric acid and the like.

JP 2003-267800 A JP 2004-244282 A JP 2011-037662 A JP 2013-064194 A

Yuji Masubuchi et al., "Preparation of apatite-type La9.33 (SiO4) 6O2 oxidion-conductor-by-alloyd-hydroids, Journal of Alloys, Vs. 408-412, pp. 641-644

  However, a method for producing a composite metal oxide having a conventional apatite-type crystal structure and having c-axis orientation as described in Patent Documents 1 and 2 described above is obtained by molding an oxide powder. Since it is a method of producing a composite metal oxide after forming a molded body, it is difficult to apply it to the production of a thin film having a film thickness of 10,000 nm or less, and the thin film cannot always be produced efficiently. It was. In addition, in the method for producing a composite metal oxide as described in Patent Document 2, a special apparatus is required to generate a strong magnetic field, which is not necessarily sufficient in that the composite metal oxide is easily produced. It was not a thing. Furthermore, since the method for producing a composite metal oxide as described in Patent Document 3 uses the above-described molten vitrification step, it is difficult to control the composition ratio of the composite metal oxide within a desired range. Thus, a complex metal oxide having an apatite type crystal structure could not be produced efficiently. In addition, in the atomic layer deposition (ALD) method as described in Patent Document 4, a complex metal oxide is produced by growing one atomic layer at a time. Metal oxide thin films could not always be produced efficiently. Furthermore, in the method described in Non-Patent Document 1, crystals are grown sufficiently uniformly so that the c-axis of the apatite-type crystal structure is sufficiently oriented in the direction perpendicular to the surface of the substrate used for manufacturing. It was difficult to make.

  As described above, even if a conventional method for producing a composite metal oxide is applied, a lanthanum silicate thin film having an apatite-type crystal structure cannot always be produced efficiently, and such a thin film is applied to the surface of a substrate. It was also impossible to obtain a film in which the c-axis was sufficiently oriented in a direction perpendicular to the film (a film having a sufficiently high c-axis orientation).

  The present invention has been made in view of the problems of the prior art, and is used for efficiently producing a lanthanum silicate thin film having an apatite type crystal structure and sufficiently high c-axis orientation. To provide a possible apatite-type lanthanum silicate precursor thin film, and to provide a method for producing an apatite-type lanthanum silicate precursor thin film capable of efficiently and reliably producing such an apatite-type lanthanum silicate precursor thin film In addition, the apatite lanthanum can sufficiently align the c-axis in a direction perpendicular to the surface of the substrate used when the substrate is used for growing a crystal, and has a sufficiently high c-axis orientation. An object is to provide a silicate thin film.

  As a result of intensive studies to achieve the above object, the present inventors have obtained an apatite-type lanthanum silicate precursor thin film, which is a precursor of a thin film made of lanthanum silicate having an apatite-type crystal structure, as a main metal element. As a composite oxide particle containing lanthanum and silicon, and the volume fraction of pores with pore diameters of 16 nm or more is 1% or less with respect to the total volume of the thin film. By using this, it has been found that a lanthanum silicate thin film having an apatite-type crystal structure and sufficiently high c-axis orientation can be efficiently produced, and the present invention is completed. It came to.

  That is, the apatite-type lanthanum silicate precursor thin film of the present invention is a thin film made of an aggregate of composite oxide particles containing lanthanum (La) and silicon (Si) as main metal elements, and has a pore size of The volume fraction of voids in the pores of 16 nm or more is 1% or less with respect to the total volume of the thin film.

  In the apatite-type lanthanum silicate precursor thin film of the present invention, the composite oxide particles are preferably made of an amorphous oxide.

  Moreover, in the apatite-type lanthanum silicate precursor thin film of the present invention, the thickness of the thin film is preferably 50 to 3000 nm.

Furthermore, the method for producing an apatite-type lanthanum silicate precursor thin film of the present invention contains a lanthanum salt and a tetraalkoxysilane in a molar ratio of lanthanum to silicon (La: Si) of 4: 3 to 5: 3. And heating the raw material solution having a pH of 3.5 to 7 under a temperature condition of 350 to 600 ° C. to precipitate composite oxide particles containing lanthanum and silicon as main metal elements,
An apatite-type lanthanum silicate precursor, which is a thin film composed of an aggregate of the composite oxide particles, and has a volume fraction of pore voids having a pore diameter of 16 nm or more with respect to the total volume of the thin film It is a method characterized by obtaining a body thin film.

The apatite-type lanthanum silicate thin film of the present invention comprises lanthanum silicate containing lanthanum (La) and silicon (Si) as main metal elements and having an apatite-type crystal structure,
When the lanthanum silicate is measured by X-ray diffraction, the peak intensity of the (002) plane and other planes other than the (001) plane (where “l” represents an integer of 1 or more). The minimum value of the ratio to the peak intensity is 10 or more,
It is characterized by.

Further, in the apatite type lanthanum silicate thin film of the present invention, the apatite type lanthanum silicate thin film is laminated on the substrate,
The average angle formed by the c-axis of the apatite-type crystal structure in the thin film and the normal of the substrate is 15 ° or less, and
The crystal orientation is aligned from one surface of the thin film to the other surface in a region of 70% or more of the volume of the thin film;
Is preferred.

  In addition, although the reason which can achieve the said objective by this invention is not necessarily certain, the present inventors guess as follows. That is, first, when an apatite-type lanthanum silicate precursor thin film of the present invention is baked to produce an apatite-type lanthanum silicate thin film, crystal nuclei are formed on the surface of the thin film and anisotropic in the film thickness direction. Therefore, when the substrate is used for growing the crystal, the crystal structure with the c-axis oriented in the film thickness direction is sufficiently uniform and sufficiently perpendicular to the surface of the substrate used. In such a direction, a film in which the c-axis of the crystal is sufficiently oriented (a film having a sufficiently high c-axis orientation in a direction perpendicular to the surface of the substrate) can be formed. In addition, the apatite-type lanthanum silicate precursor thin film of the present invention has a sufficiently small volume fraction of voids of coarse pores having a pore diameter of 16 nm or more and 1% or less with respect to the total volume of the thin film. . Thus, since the apatite-type lanthanum silicate precursor thin film of the present invention has a small proportion of large pores that inhibit the crystal growth, it is possible to grow the crystal more efficiently. Thus, the apatite-type lanthanum silicate precursor thin film of the present invention has a small proportion of large pores that inhibit crystal growth between the aggregates of the composite oxide particles that are the precursors of the lanthanum silicate. Therefore, even at a relatively low firing temperature, crystals can be grown so as to have sufficiently high orientation, and a lanthanum silicate thin film having sufficiently high orientation can be efficiently formed. Therefore, by using the apatite type lanthanum silicate precursor thin film of the present invention, it becomes possible not only to efficiently produce a lanthanum silicate thin film having an apatite type crystal structure, but also to measure the crystal structure by X-ray diffraction. In this case, the minimum value of the ratio between the peak intensity of the (002) plane and the peak intensity of other planes other than the (001) plane (where l is an integer of 1 or more) is 10 or more. As described above, the present inventors can obtain a lanthanum silicate thin film in which the c-axis of the crystal is sufficiently oriented in a direction perpendicular to the surface of the substrate and has a sufficiently high c-axis orientation. I guess. The apatite-type lanthanum silicate precursor thin film of the present invention is obtained by heating the raw material solution as described above under a temperature condition of 350 to 600 ° C. to obtain composite oxide particles containing lanthanum and silicon as main metal elements. It can manufacture by making it precipitate. For this reason, the apatite-type lanthanum silicate precursor thin film of the present invention does not require special equipment or the like for its production, and it can be said that it is advantageous from the viewpoint of cost and production. Further, since the apatite-type lanthanum silicate precursor thin film can be manufactured by firing at a relatively low temperature condition as described above, an apatite-type lanthanum silicate thin film can be manufactured. There is no need to provide special and expensive equipment in the process. From the viewpoint of not requiring such expensive equipment, it can be said that the apatite-type lanthanum silicate precursor thin film of the present invention is a material that is sufficiently excellent in the productivity of the apatite-type lanthanum silicate thin film. Thus, the present inventors speculate that according to the apatite-type lanthanum silicate precursor thin film of the present invention, a lanthanum silicate thin film having an apatite-type crystal structure can be produced sufficiently efficiently. .

  According to the present invention, there is provided an apatite type lanthanum silicate precursor thin film that can be used for efficiently producing a lanthanum silicate thin film having an apatite type crystal structure and sufficiently high c-axis orientation. , To provide a method for producing an apatite-type lanthanum silicate precursor thin film capable of efficiently and reliably producing such an apatite-type lanthanum silicate precursor thin film, and to use a substrate when growing a crystal The c-axis can be sufficiently oriented in a direction perpendicular to the surface of the substrate used in the case, and an apatite-type lanthanum silicate thin film having a sufficiently high c-axis orientation can be provided.

It is a graph which shows the XRD pattern (The relationship between an arbitrary unit intensity | strength and angle (2 (theta))) of the thin film obtained in Example 1. FIG. 2 is a scanning electron micrograph (cross-sectional SEM image of a thin film) showing a cross section of the thin film obtained in Example 1. FIG. It is a graph which shows the relationship between the pore size (radius: unit nm) of the thin film obtained in Example 1, and the relative volume ratio (volume distribution: f (R)) of a pore. It is a graph which shows the XRD pattern (The relationship between an arbitrary unit intensity | strength and angle (2 (theta))) of the thin film obtained in Example 2. FIG. 4 is a transmission electron micrograph (cross-sectional TEM image of a thin film) showing a cross section of the thin film obtained in Example 2. FIG. 4 is a limited-field electron beam diffraction image (electron micrograph) of the surface side region of the thin film obtained in Example 2. FIG. 4 is a limited-field electron beam diffraction image (electron micrograph) of a region on the substrate side of the thin film obtained in Example 2. FIG. 2 is a scanning electron micrograph (cross-sectional SEM image of a thin film) showing a cross section of the thin film obtained in Comparative Example 1. FIG. It is a graph which shows the relationship between the pore size (radius: unit nm) of the thin film obtained by the comparative example 1, and the relative volume ratio (volume distribution: f (R)) of a pore. It is a graph which shows the XRD pattern (The relationship between the intensity | strength of arbitrary units, and an angle (2 (theta))) of the thin film obtained in the comparative example 2. It is a graph which shows the XRD pattern (The relationship between an arbitrary unit intensity | strength and angle (2 (theta))) of the thin film obtained in Example 4. FIG. It is a scanning electron micrograph (cross-sectional SEM image of a thin film) which shows the cross section of the thin film obtained by the comparative example 3. It is a graph which shows the XRD pattern (The relationship between the intensity | strength of arbitrary units, and an angle (2 (theta))) of the thin film obtained by the comparative example 4.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

[Apatite-type lanthanum silicate precursor thin film]
The apatite-type lanthanum silicate precursor thin film of the present invention is a thin film made of an aggregate of composite oxide particles containing lanthanum and silicon as main metal elements, and pores having a pore diameter of 16 nm or more. The volume fraction is 1% or less of the total volume of the thin film.

  The composite oxide particles forming such a thin film contain lanthanum (La) and silicon (Si) as main metal elements. The total amount (total amount) of lanthanum and silicon contained as main metal elements in such oxide particles is preferably 95 at% or more with respect to all metal elements in the oxide particles, and 99 at% or more. It is more preferable that it is 99.9-100 at%. When satisfying such lanthanum and silicon content conditions, it can be said that lanthanum and silicon are the main components (main metal elements) of the metal elements forming the composite oxide particles.

In such composite oxide particles, the content ratio of lanthanum and silicon is preferably 4: 3 to 5: 3 in terms of molar ratio (La: Si), and 9.33: 6 to 9.5: 6 is more preferable. When the content ratio of lanthanum is less than the lower limit, tetragonal lanthanum silicate (La ₂ Si ₂ O ₇ ) or monoclinic lanthanum silicate (La ₂ ) is contained in the lanthanum silicate film obtained by firing the thin film. SiO ₅₎ contains sufficiently tends to be difficult to form a thin film of c-axis oriented highly apatitic lanthanum silicate, whereas if it exceeds the upper limit, obtained by firing the thin lanthanum Monoclinic lanthanum silicate (La ₂ SiO ₅ ) is contained in the silicate film, and it tends to be difficult to form an apatite lanthanum silicate thin film with sufficiently high c-axis orientation.

  The composite oxide particles contain lanthanum (La) and silicon (Si) as main metal elements, and may contain other metal elements other than La and Si. In such composite oxide particles containing other metal elements, from the viewpoint of ionic valence, a part of La in the composite oxide particles is an alkaline earth metal element such as Pr, Nd, Sr or a rare earth element. And a part of Si in the composite oxide particle may be substituted with 3B group, 4B group, 5B group such as Al, Ge, etc., and La and Si in the composite oxide particle may be substituted. A part of both may be substituted with the metal element as described above. Thus, in the composite oxide particles, a part of La and / or a part of Si may be substituted with another metal element, and the other metal element is suitably suitable from the viewpoint of ionic valence. You can select and use anything.

  The “composite oxide” referred to here is composed of a plurality of metal oxides including at least a lanthanum oxide and a silicon oxide, and these metal oxides are at least partially dissolved. This means that a simple physical mixture of metal oxides is not included. Further, the state of such a complex oxide is such that, in an X-ray diffraction pattern (XRD pattern) obtained by X-ray diffraction measurement, an angle (2θ) is around 28 ° (28 ° ± 2 °) and around 45 ° (45 This can be confirmed by the presence or absence of a broad peak (halo) at a position of ± 2 °. Thus, in the present invention, when there is a broad peak (halo) at a position where the angle (2θ) is around 28 ° (28 ° ± 2 °) and around 45 ° (45 ° ± 2 °), The lanthanum oxide and the silicon oxide are judged to be a composite oxide in which at least a part thereof is in solid solution. Note that the broad peak (halo) referred to here is a peak having a half-value width exceeding 5 °.

  Further, the composite oxide constituting such composite oxide particles is preferably amorphous. That is, the composite oxide particles are preferably made of an amorphous oxide. The “amorphous oxide” referred to here is an X-ray diffraction (XRD) apparatus (for example, trade name “RINT-TTR (Cu—Kα line)” manufactured by Rigaku Corporation). When X-ray diffraction measurement is performed using 1 g as a measurement sample, it can be confirmed that there is no peak (sharp peak) in which the half-value width is 2 ° or less in the obtained X-ray diffraction pattern (XRD pattern) Say. Thus, in the present invention, based on the XRD pattern, whether or not the composite oxide particles are “amorphous” is determined based on the presence or absence of a sharp peak.

  Furthermore, the average particle diameter of such composite oxide particles is not particularly limited, but is preferably 50 nm or less, more preferably 20 nm or less (more preferably 1 to 20 nm). If the average particle size is less than the lower limit, the production of particles tends to be difficult. On the other hand, if the upper limit is exceeded, the volume fraction of pore voids such that the pore size is 16 nm or more increases. Tend to. In addition, such an average particle diameter is an average obtained by measuring a diameter based on a scanning electron microscope image for any 100 or more particles (at least 100 or more arbitrary particles) of the composite oxide particles. It can be obtained by calculating the value. More specifically, any 100 or more particles (at least 100 or more arbitrary particles) of the composite oxide particles are measured with an electron microscope (scanning electron microscope), and the obtained electron microscope image (scanning type) By setting a threshold value in the electron microscope image), clarifying the edge (淵) of the particle in the image, measuring the diameter by approximating the shape of the edge of each particle to a circle, and calculating the average value Can be sought. Here, the “threshold value” is set in order to binarize the particles in the electron microscope image and other portions so as to be clearly distinguished, and is set to 80% of the maximum luminance, for example. Can do. The term “measure the diameter by approximating the shape of the edge of each particle to a circle” here refers to the diameter (Heywood diameter) of the circle corresponding to the projected area of the particle as the “particle diameter” of each particle. And measuring the diameter. That is, when the particle is not a true sphere, the diameter of the circle corresponding to the circle of the same area is obtained based on the projected area of the particle in order to approximate the circle, and the diameter (Heywood diameter) of each particle is calculated. Adopted as “particle diameter”. The average particle diameter is calculated using, for example, a scanning electron microscope (for example, a scanning electron microscope manufactured by Hitachi High-Technology Corporation: trade name “S-5500”) as a measuring device, and image analysis software. As “ImageJ” of the National Institutes of Health.

  The apatite-type lanthanum silicate precursor thin film of the present invention is a thin film made of an aggregate of the composite oxide particles. Such an aggregate state of composite oxide particles (whether or not they are aggregates) can be confirmed by cross-sectional observation with a scanning electron microscope or confirmation of open pores (presence or absence of BET adsorption isotherm hysteris). it can. Moreover, as thickness of such a thin film, it is more preferable that it is 50-3000 nm, and it is still more preferable that it is 100-800 nm. If the thickness of such a thin film is less than the lower limit, the c-axis orientation of the lanthanum silicate thin film obtained by firing the precursor thin film tends to decrease, whereas if the upper limit is exceeded, a thin film is formed on the substrate. When the film is formed, peeling from the substrate tends to occur easily. Note that the thickness of such a thin film is at least three or more fields of view (in addition, one field of view includes a region including at least both surfaces of the thin film (if the thin film is formed on the substrate, the cross section The region from the substrate to the region including the surface of the film), the film occupies 40% or more of the vertical length of the field of view, and the lateral width of the film in the field of view is 1.5 times or more the film thickness. In this case, the cross section of the measurement sample is measured with a scanning electron microscope, and the distance between both surfaces of the film in the obtained scanning electron microscope image of each field of view is obtained as the film thickness. The average value is adopted. The distance between both surfaces of the film in each field of view is, for example, an approximate straight line (hereinafter, referred to as “first straight line” in some cases) by the least square method with respect to the edge of one surface (one surface) of the film. After drawing, the other surface (the other surface) is referred to as a straight line (hereinafter sometimes referred to as a “second straight line”) parallel to the approximate straight line (first straight line) as described later. ) To obtain the distance between the two straight lines, and the distance between the two straight lines can be measured as the distance between both surfaces of the film. Such a second straight line (straight line to be drawn later) is first formed for each visual field by obtaining the area of the film in the visual field by image processing, the two straight lines, and the edge of the visual field. Draw so that the area of the parallelogram matches. In the case where a thin film is formed on the substrate, first, an approximate straight line is drawn with respect to the substrate surface instead of the first straight line, and the straight line is regarded as the first straight line. As described above, the distance between the two straight lines may be obtained by drawing the second straight line, and the distance between the two straight lines may be measured as the distance between both surfaces of the film. However, the substrate is a silicon substrate (Si substrate) such as a Si (100) substrate or a quartz substrate, and the distance between the concave and convex portions on the surface of the film has a size of 2% or less of the desired film thickness. In this case, instead of the first straight line, a straight line connecting the two intersections of the substrate surface and the edge of the field of view is drawn first, and then the film parallel to the straight line instead of the second straight line. A straight line on the surface is drawn (note that the straight line on the film surface is drawn at a position where the distance is equal to the lowest point of the concave portion on the film surface and the apex of the convex portion on the film surface). The distance between the straight lines may be obtained, and the distance between these straight lines may be measured as the distance between both surfaces of the film. In this way, the distance between both surfaces of the film is obtained in any three or more visual fields, and the averaged value is adopted as the thickness value (film thickness) of the thin film.

  Further, the apatite-type lanthanum silicate precursor thin film of the present invention has a volume fraction (volume ratio) of pores having a pore diameter of 16 nm or more with respect to the total volume of the thin film of 1% or less. . As described above, the apatite-type lanthanum silicate precursor thin film of the present invention has a sufficiently low ratio of relatively large pores having a pore diameter of 16 nm or more. When the volume fraction of pore voids having such pore diameters of 16 nm or more exceeds the above upper limit, the voids between the particles increase, and the crystal growth causes a large interval with other particles. Thus, it becomes difficult to grow a crystal sufficiently uniformly, and it becomes difficult to efficiently produce a crystal structure having a sufficiently high orientation even when the precursor thin film is fired. Further, from the same viewpoint, the volume fraction of the voids of the pores having a pore diameter of 16 nm or more (volume ratio) is more preferably 0.5% or less with respect to the total volume of the thin film, More preferably, it is 0.1% or less. If the pore diameter is less than 16 nm, crystal growth is not hindered during firing. Therefore, when the precursor thin film is fired, an apatite crystal structure thin film having sufficiently high orientation is obtained. It is possible to manufacture more efficiently.

  Here, the volume fraction of pore voids having a pore diameter of 16 nm or more can be calculated as follows. That is, first, with a scanning electron microscope (SEM), a measurement region having four or more fields of view with respect to the cross section of the thin film (the measurement region is a region of vertical: 475 nm, horizontal: 635 nm, including both surfaces of the film) (Measurement field of view is preferable.) Is measured, and the area ratio around each field of view (cross-section measurement region) of pores of 16 nm or more (pores of 16 nm or more in the film within the measurement surface (measurement field of measurement)) It is possible to calculate by averaging the area ratio for each measurement region (cross section) obtained. Since the volume is obtained by integration of the surface, the average value (%) of the area ratio around each visual field of pores of 16 nm or more obtained by such cross-sectional measurement is, as a result, volume fraction (%) and pseudo control. Therefore, the average value of the area ratio around each visual field of pores of 16 nm or more obtained by the calculation method as described above is regarded as the volume fraction of pore voids having a pore diameter of 16 nm or more as it is. Can be used. Thus, the volume fraction of pore voids having a pore diameter of 16 nm or more can be calculated by the calculation method as described above. When measuring the volume fraction of pore voids with a pore diameter of 16 nm or more, if the cross section of the pores confirmed in each field of view is not a circle (if the pores are not measured in a circular shape in the cross section) ), The diameter of a circle having an area corresponding to the cross-sectional area of the pore is adopted as the pore diameter.

  Moreover, in the apatite type lanthanum silicate precursor thin film of the present invention, the average pore diameter is preferably 1 to 16 nm, and more preferably 1 to 10 nm. When the average pore diameter is less than the lower limit, peeling of the film tends to occur. On the other hand, when the average pore diameter exceeds the upper limit, it tends to be difficult to obtain a film having sufficiently high orientation. As such an average pore diameter, an X-ray scattering pattern (scattering intensity pattern) is obtained by a small-angle X-ray scattering method using a small-angle X-ray diffractometer (for example, trade name “NANO-Viewer” manufactured by Rigaku Corporation). ), And a value obtained using analysis software (for example, software “Irena” developed by J. Ilavsky of Argonne National Laboratory [Argonne National Laboratory]) can be employed.

  The method for producing such an apatite-type lanthanum silicate precursor thin film is not particularly limited, but the method for producing an apatite-type lanthanum silicate precursor thin film of the present invention described later can be suitably used.

  In addition, in the apatite-type lanthanum silicate precursor thin film of the present invention, the c-axis is sufficiently oriented in the film thickness direction even when the apatite-type lanthanum silicate precursor thin film is fired at a relatively low firing temperature (for example, 800 to 1200 ° C.). It is possible to manufacture a thin film made of lanthanum silicate having an apatite type crystal structure with sufficiently high orientation. That is, by using the apatite-type lanthanum silicate precursor thin film of the present invention, it is possible to obtain a lanthanum silicate thin film in which the c-axis is sufficiently oriented in the film thickness direction at a relatively low firing temperature of 800 to 1200 ° C. is there. Therefore, the apatite-type lanthanum silicate precursor thin film of the present invention is particularly useful as a material for forming an apatite-type lanthanum silicate thin film for use as an oxide ion conductor.

  The apatite-type lanthanum silicate precursor thin film of the present invention has been described above. Hereinafter, the method for producing the apatite-type lanthanum silicate precursor thin film of the present invention will be described.

[Method for producing apatite-type lanthanum silicate precursor thin film]
The method for producing an apatite-type lanthanum silicate precursor thin film of the present invention comprises a lanthanum salt and tetraalkoxysilane in a molar ratio of lanthanum to silicon (La: Si) of 4: 3 to 5: 3, and By heating a raw material solution having a pH of 3.5 to 7 under a temperature condition of 350 to 600 ° C., and depositing composite oxide particles containing lanthanum and silicon as main metal elements,
An apatite-type lanthanum silicate precursor, which is a thin film composed of an aggregate of the composite oxide particles, and has a volume fraction of pore voids having a pore diameter of 16 nm or more with respect to the total volume of the thin film It is a method characterized by obtaining a body thin film.

In such a method for producing an apatite-type lanthanum silicate precursor thin film, a raw material solution containing a lanthanum salt and tetraalkoxysilane is used. Such a lanthanum salt is not particularly limited, and for example, nitrates (La (NO ₃ ) ₃ ), sulfates, acetates, halides, citrates and the like can be used as appropriate. Among such lanthanum salts, nitrate (La (NO ₃ ) ₃ ) and acetate are preferably used, and nitrate (La (NO ₃ ) ₃ ) is more preferable from the viewpoint of suppressing the mixing of anionic elements. preferable. In addition, as such a salt, a hydrate may be utilized and a commercial item may be utilized.

  Moreover, although it does not restrict | limit especially as said tetraalkoxysilane, The tetraalkoxysilane whose carbon number of four alkoxy groups is all 1-10 (more preferably 1-6, still more preferably 1-3) is preferable. When the number of carbons exceeds the upper limit, volume shrinkage due to thermal decomposition increases, and the volume fraction of pores having a pore diameter of 16 nm or more tends to increase. Furthermore, examples of such tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane, and the like, which further reduce volume shrinkage during thermal decomposition. From the viewpoint, those having smaller alkoxy groups are desirable, among which tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane are more preferable, and tetraethoxysilane is still more preferable.

  Moreover, it is preferable that such a raw material solution contains a solvent. As such a solvent, water, alcohol, a mixed solvent thereof or the like can be preferably used. Examples of such alcohols include methanol, ethanol, isopropanol, n-propanol, ethylene glycol, glycerin, butanol, or a mixture thereof. Moreover, as such a solvent, it is preferable that it is a mixed solvent of water and alcohol from a viewpoint of suppression of mixing of the element of a solvent, and volatility. The amount of alcohol contained in the mixed solvent of water and alcohol is not particularly limited, but is preferably 50 to 100% by volume with respect to the total amount of the solvent. If the content of such an alcohol is less than the lower limit, the tetraalkoxysilane tends to be difficult to dissolve.

In such a raw material solution, a lanthanum salt and tetraalkoxysilane are mixed in a molar ratio of lanthanum to silicon (La: Si) of 4: 3 to 5: 3 (more preferably 4.665: 3 to 4). 750: 3). When the ratio of silicon to lanthanum is less than the lower limit, tetragonal lanthanum silicate (La ₂ Si ₂ O ₇ ) or monoclinic lanthanum silicate (La ₂ SiO ₅ ) is produced when the precursor thin film is fired. A lanthanum silicate thin film that is by-produced and has a sufficiently high c-axis orientation cannot be obtained. On the other hand, when the upper limit is exceeded, monoclinic lanthanum silicate (La) is produced when the precursor thin film is fired. ₂ SiO ₅ ) is by-produced, and a lanthanum silicate thin film with sufficiently high orientation in the c-axis direction cannot be obtained.

  Furthermore, in such a raw material solution, the content of the lanthanum salt is preferably 0.01 to 0.40 mol / L, and more preferably 0.05 to 0.167 mol / L. When the content (concentration) of such a lanthanum salt is less than the lower limit, it tends to take time to increase the film thickness. On the other hand, when the upper limit is exceeded, pores having a pore diameter of 16 nm or more increase. There is a tendency.

  Moreover, it is preferable that content of tetraalkoxysilane is 0.01-0.3 mol / L, and it is more preferable that it is 0.05-0.1 mol / L. When the tetraalkoxysilane content (concentration) is less than the lower limit, it tends to take time to increase the film thickness. On the other hand, when the upper limit is exceeded, pores having a pore diameter of 16 nm or more are present. It tends to increase.

Furthermore, such a raw material solution needs to have a pH of 3.5-7. When such a pH value is less than the lower limit, the number of pores having a pore diameter of 16 nm or more increases, and the volume fraction of pores having a pore diameter of 16 nm or more is 1 with respect to the total volume of the thin film. % Of apatite-type lanthanum silicate precursor thin film cannot be obtained. On the other hand, when the upper limit is exceeded, lanthanum ions are precipitated as lanthanum hydroxide, so when the precursor thin film is baked, La ₂ O ₃ and La ₂ Si ₂ O ₇ is by-produced, and it becomes difficult to obtain a lanthanum silicate thin film with sufficiently high orientation in the c-axis direction. Moreover, as pH of such a raw material solution, it is more preferable that it is 3.5-6.0 from the same viewpoint, and it is still more preferable that it is 4.5-6.0.

  Moreover, the preparation method of such a raw material solution is not particularly limited. For example, each raw material (lanthanum salt and tetraalkoxysilane) is added to the solvent and mixed (hereinafter referred to as “method” in some cases). Any method can be used as long as it is a method capable of preparing the raw material solution. As such a method (A), for example, after adding a lanthanum salt in the solvent, tetraalkoxysilane may be added and mixed, or a lanthanum salt may be added in water. Then, after obtaining a mixed solution, an alcohol may be added thereto, and then tetraalkoxysilane may be added and mixed. The order of adding the lanthanum salt and tetraalkoxysilane is not particularly limited, but the temperature of the raw material solution increases in a state containing tetraalkoxysilane (for example, alcohol and water in a state containing tetraalkoxysilane). From the standpoint of more sufficiently preventing the temperature from increasing when the lanthanum is mixed, first, a solution (mixture) containing a lanthanum salt is prepared, and then tetraalkoxysilane is added thereto. It is preferable to add and mix.

  Moreover, the mixing process in the case of preparation of such a raw material solution is not restrict | limited, You may utilize suitably the apparatus for stirring (for example, magnetic stirrer etc.) suitably. Furthermore, when preparing such a raw material solution, the temperature and temperature of 1 to 40 ° C. (more preferably 1 to 25 ° C.) are used so that the hydrolysis and polymerization of the tetraalkoxysilane do not proceed before using the raw material solution. The raw materials (lanthanum salt and tetraalkoxysilane) are preferably added to the solvent and mixed. If the temperature is lower than the lower limit, the solvent is solidified, so that the preparation of the raw material solution tends to be difficult. On the other hand, if the upper limit is exceeded, hydrolysis and polymerization of the tetraalkoxysilane easily proceed in the solvent. As a result, coarse particles of silicon oxide are easily formed in the raw material solution. When a thin film is formed using a raw material solution containing such coarse particles, a large void (hole) is generated in the thin film due to such coarse particles, and the thin film Even if calcined, crystallization cannot be achieved sufficiently efficiently, and an apatite-type lanthanum silicate thin film having a sufficiently high orientation tends not to be obtained. In addition, the temperature conditions at the time of preparation of the raw material solution are sufficient to suppress the progress of hydrolysis and polymerization of tetraalkoxysilane depending on the type of tetraalkoxysilane used and the time until use (storage time). What is necessary is just to select suitably the temperature which can be performed.

  Thus, the raw material solution is preferably prepared under a temperature condition of 1 to 40 ° C. (more preferably 1 to 25 ° C.). In addition, the raw material solution may be used as soon as possible after preparation (without any time after preparation) from the viewpoint of sufficiently suppressing the hydrolysis and polymerization of tetraalkoxysilane in the raw material solution. preferable. For example, when tetraethoxysilane is used as tetraalkoxysilane and the raw material solution is prepared at room temperature, it is preferably used within 2 hours. Regarding the time to use after preparation of such a raw material solution, according to the Arrhenius equation, the lower the temperature, the more sufficiently the hydrolysis and polymerization of tetraalkoxysilane can be suppressed in the raw material solution. I understand.

  Further, such a raw material solution is preferably used as it is without being subjected to other treatments such as a reflux treatment before being used (before being heated at a temperature condition of 350 to 600 ° C. described later). As described in Non-Patent Document 1, when the raw material solution is subjected to other treatment such as reflux treatment before the heat treatment, hydrolysis and polymerization of the tetraalkoxysilane proceed remarkably. It is difficult to sufficiently suppress the generation of coarse pores having a diameter of 16 nm or more. Therefore, the raw material solution can be used as it is without being subjected to other treatments such as a reflux treatment before preparation (before the particles are precipitated) after the preparation and before the treatment for heating at a temperature of 350 to 600 ° C. preferable.

  Thus, from the viewpoint of sufficiently suppressing the progress of hydrolysis and polymerization of tetraalkoxysilane in the solution before using the raw material solution, the raw material solution is 1 to 40 ° C. (more preferably After preparation under temperature conditions of 1 to 25 ° C., as early as possible (more preferably within 2 hours after preparation, more preferably within 1 hour after preparation, particularly preferably within 0.5 hour after preparation, most preferably preparation) Immediately thereafter, it is used as it is (used in a fresher state) at a temperature of 350 to 600 ° C. in order to precipitate composite oxide particles containing lanthanum and silicon from such a solution. It is preferable to perform a heating treatment. Thus, as the raw material solution, it is preferable to use a raw material solution in a state where hydrolysis or polymerization of tetraalkoxysilane does not proceed. Thus, by using the raw material solution in a state where hydrolysis or polymerization of tetraalkoxysilane has not progressed, it is possible to sufficiently suppress the generation of coarse particles of silicon oxide at the time of thin film formation, and a large size of 16 nm or more. The generation of pores can be more sufficiently suppressed.

  Further, in the present invention, a composite oxide particle containing lanthanum and silicon as main metal elements by heating the raw material solution at a temperature of 350 to 600 ° C. using the raw material solution as described above. And a volume fraction of pore voids having a pore diameter of 16 nm or more is 1% or less with respect to the total volume of the thin film. An apatite-type lanthanum silicate precursor thin film is obtained.

  Thus, in the present invention, the heating temperature condition for precipitating the composite oxide particles from the raw material solution needs to be 350 to 600 ° C. The heating temperature is such that the lanthanum salt and tetraalkoxysilane are thermally decomposed to precipitate lanthanum oxide and silicon oxide, so that at least a part thereof can be dissolved. From the standpoint that the oxide particles can be deposited at a temperature at which the deposited composite oxide particles are not crystallized by heat, the temperature range (350 to 600 ° C.) is selected. A suitable temperature may be appropriately adopted depending on the raw material to be used. If the temperature condition of such heating is less than the above lower limit, the thermal decomposition of the lanthanum salt becomes insufficient, and it becomes impossible to sufficiently form particles made of the composite oxide. When the precursor particles are crystallized and an amorphous precursor thin film cannot be obtained and the precursor thin film is baked, the c-axis is sufficiently oriented (the degree of c-axis orientation is sufficiently high). The thin film cannot be formed. In addition, the heating temperature condition for precipitating such composite oxide particles varies depending on the type of raw material compounds (lanthanum salt and tetraalkoxysilane) used, and therefore cannot always be said. From the viewpoint of ease of work, 350 to 500 ° C is more preferable, and 400 to 500 ° C is still more preferable.

  In addition, from the viewpoint of forming a thin film more efficiently using such a raw material solution, the step (I) of heating at the temperature condition (350 to 600 ° C.) after applying the raw material solution on the substrate is performed. It is preferable to adopt. Such a substrate is not particularly limited, but a known substrate that can be used when forming a thin film made of a complex oxide can be used as appropriate. For example, the substrate is made of Si (100) substrate or quartz glass. Examples include a substrate, a substrate using Ni (Ni plate or the like), porous NiO, and the like. Among these, a Si (100) substrate and a quartz glass substrate are preferable from the viewpoint that a thin film having a flat surface can be more easily produced. In addition, as such a quartz glass substrate and Si (100) substrate (a silicon substrate whose surface is a (100) plane), commercially available products can be used as appropriate.

  Further, a method (coating method) for applying the raw material solution on such a substrate is not particularly limited, and a known coating method can be appropriately used, and examples thereof include a spin coating method, a dip coating method, and a spray coating method. It is done. In addition, suitable conditions (for example, conditions for the number of rotations and the number of seconds when spin coating is employed) used in such a coating method are not particularly limited, and the shape and size of the substrate, the raw material in the solution Based on the concentration, wettability of the substrate surface to the solution, and the like, appropriate conditions may be appropriately adopted so that a sufficiently thin uniform coating film is obtained.

  In addition, when adopting the step (I), it is possible to make the thickness of the thin film to be manufactured to a desired thickness by repeatedly performing the step (I) according to the design of the thin film to be manufactured. .

  When step (I) is repeated a plurality of times, for example, each time step (I) is performed, the substrate after heating at the temperature condition (350 to 600 ° C.) is set to a cooling temperature of 1 to 40 ° C. It is preferable to cool (more preferably 10 to 40 ° C, more preferably about room temperature (25 ° C)). That is, when the step (I) is repeated a plurality of times, the substrate is 1 to 40 ° C. (more preferably 10 to 40 ° C., more preferably 10 to 25 ° C.) in the stage before each step (I) is performed. It is preferable to be cooled. When the cooling temperature is lower than the lower limit, the solvent tends to solidify when the raw material solution is applied. On the other hand, when the upper limit is exceeded, the solvent is uniform due to boiling and volatilization when the raw material solution is applied. There is a tendency that a film cannot be obtained.

  In addition, as an atmospheric condition that can be adopted when the step of heating the raw material solution at a temperature of 350 to 600 ° C. is performed, from the viewpoint of accelerating the oxidative decomposition of counter anions and carbides and requiring no special equipment. For example, it can be under atmospheric conditions (in the atmosphere). Thus, a thin film can be efficiently produced by a simple process such as heating in the atmosphere.

  Thus, by using the raw material solution, heating the raw material solution at a temperature of 350 to 600 ° C., and precipitating composite oxide particles containing lanthanum and silicon as main metal elements, An apatite-type lanthanum silicate precursor, which is a thin film composed of an aggregate of composite oxide particles, and the volume fraction of pores having a pore diameter of 16 nm or more is 1% or less with respect to the total volume of the thin film A thin film can be obtained. Such a thin film (such as the composite oxide particles constituting the film and the volume fraction of pores having a specific pore diameter) is the above-mentioned apatite-type lanthanum silicate precursor thin film of the present invention. It is the same as that described (the preferred one is also the same). Further, when the composite oxide particles constituting such a thin film contain a metal element other than lanthanum and silicon as described above, the raw material solution appropriately contains a salt of the other metal element. You can do it. Thus, in the present invention, the obtained apatite type lanthanum silicate precursor thin film is the same as the apatite type lanthanum silicate precursor thin film of the present invention.

  It should be noted that the volume fraction of pore voids having a pore diameter of 16 nm or more, which is a thin film comprising an aggregate of the composite oxide particles, by the method for producing an apatite-type lanthanum silicate precursor thin film of the present invention. The reason why it is possible to obtain an apatite-type lanthanum silicate precursor thin film having a rate of 1% or less with respect to the total volume of the thin film is not necessarily clear, but the present inventors infer as follows. That is, in such a method for producing an apatite-type lanthanum silicate precursor thin film of the present invention, first, the raw material solution is heated (for example, the raw material solution is heated after being applied to the substrate. To deposit metal oxide particles. At the time of precipitation of such particles, the particles are precipitated from the raw material solution by heating at a relatively low temperature of 350 to 600 ° C. Therefore, it is possible to more efficiently form amorphous composite oxide particles. Oxide particles and silicon oxide particles are deposited in a well-mixed and dispersed state at the nanoscale, and at least a part of these particles is dissolved to form a fine composite oxide. As a result, a thin film is formed. Since the composite oxide can be made into an aggregate of fine particles in this way, the obtained thin film has a pore volume fraction (volume ratio) of pores having a pore diameter of 16 nm or more. It can be 1% or less of the product. In addition, in such a method for producing an apatite-type lanthanum silicate precursor thin film of the present invention, for example, when a raw material solution is applied to a substrate, the size of the oxide particles to be deposited is appropriately controlled by controlling the thickness of the applied film. Can be more efficiently controlled to a fine state. Thus, when the size of the deposited particles is controlled by appropriately controlling the thickness of the coating film of the raw material solution, fine oxide particles can be deposited more uniformly on the substrate. Thus, the volume fraction (volume ratio) of the pore voids having a pore diameter of 16 nm or more in the thin film composed of the composite oxide particle aggregate is less than 1% with respect to the total volume of the thin film. The present inventors speculate that it is possible to make this.

  Thus, according to the method for producing an apatite-type lanthanum silicate precursor thin film of the present invention, the obtained apatite-type lanthanum silicate precursor thin film is the same as the apatite-type lanthanum silicate precursor thin film of the present invention described above. be able to. Therefore, the method for producing an apatite-type lanthanum silicate precursor thin film of the present invention can be suitably employed as a method for producing the apatite-type lanthanum silicate precursor thin film of the present invention. Further, the method for producing an apatite-type lanthanum silicate precursor thin film of the present invention can produce the apatite-type lanthanum silicate precursor thin film of the present invention by a simple process such as heating using the raw material solution. It can be said that this is an advantageous method in terms of productivity including cost.

  The manufacturing method of the apatite-type lanthanum silicate precursor thin film of the present invention has been described above. Hereinafter, the apatite-type lanthanum silicate thin film of the present invention will be described.

[Apatite-type lanthanum silicate thin film]
The apatite-type lanthanum silicate thin film of the present invention comprises lanthanum silicate containing lanthanum (La) and silicon (Si) as main metal elements and having an apatite-type crystal structure,
When the lanthanum silicate is measured by X-ray diffraction, the peak intensity of the (002) plane and the peak intensity of other planes other than the (001) plane (where l is an integer of 1 or more) The minimum ratio is 10 or more,
It is characterized by.

  Such an apatite-type lanthanum silicate thin film of the present invention comprises a lanthanum silicate having an apatite-type crystal structure. Such a lanthanum silicate contains lanthanum (La) and silicon (Si) as main metal elements. The total amount (total amount) of lanthanum and silicon in such a lanthanum silicate is preferably 95 at% or more, more preferably 99 at% or more, based on all metal elements in the oxide particles. More preferably, it is 9-100 at%, and it is especially preferable that it is 100 at%. In addition, when satisfy | filling the conditions of content of such lanthanum and silicon, it can be said that lanthanum and silicon are the main components (main metal element) of the metal element which forms the said composite oxide particle.

In such apatite-type lanthanum silicate, the content ratio of lanthanum and silicon is preferably 4: 3 to 5: 3 in terms of molar ratio (La: Si), and 4.665: 3 to 4.75. : 3 is more preferable. When the content ratio of lanthanum is less than the lower limit, tetragonal lanthanum silicate (La ₂ Si ₂ O ₇ ) and monoclinic lanthanum silicate (La ₂ SiO ₅ ) are included, and (002) plane The minimum value of the ratio between the intensity of the peak and the intensity of the peak of the other face other than the (00l) face (where l is an integer of 1 or more) tends to be less than 10, while the upper limit Is included, monoclinic lanthanum silicate (La ₂ SiO ₅ ) is included in the film, and the peak intensity on the (002) plane and other than the (00l) plane (where l is an integer of 1 or more) The minimum value of the ratio to the peak intensity on the other surface tends to be less than 10.

In addition, as such a lanthanum silicate, a composition formula: La _x Si ₆ O _{12 + 1.5x} [wherein x represents a numerical value of 8 or more and 10 or less (in other words, x represents a condition: 8 ≦ x ≦ 10) It is a numerical value that meets.)]. ) Is preferable. When the value of x in such a composition formula is less than the lower limit, tetragonal lanthanum silicate (La ₂ Si ₂ O ₇ ) and monoclinic lanthanum silicate (La ₂ SiO ₅ ) are included, The minimum value of the ratio between the peak intensity of the (002) plane and the peak intensity of other planes other than the (001) plane (where l represents an integer of 1 or more) tends to be less than 10, while When the above upper limit is exceeded, monoclinic lanthanum silicate (La ₂ SiO ₅ ) is contained in the film, and the peak intensity on the (002) plane and other than the (001) plane (where l is 1 or more) The minimum value of the ratio to the intensity of the peak on the other surface tends to be less than 10. Such a composition can be confirmed by energy dispersive X-ray spectroscopy, secondary ion mass spectrometry, atomic absorption and the like.

The apatite type crystal structure possessed by the lanthanum silicate belongs to the hexagonal system in terms of crystallography, and has two crystal faces, a (b) face and c face. In the present invention, the apatite-type crystal structure of the lanthanum silicate is a crystal structure in which the main phase of the hexagonal apatite structure (space group: P6 ₃ / m) is confirmed in the X-ray diffraction (XRD) pattern. Good. That is, the “apatite-type crystal structure” here may be a structure in which the peak position coincides with the JCPDS card 49-0443 in the X-ray diffraction pattern. The measurement method (X-ray diffraction pattern measurement method) of such a crystal structure by X-ray diffraction is not particularly limited, but an X-ray diffraction (XRD) apparatus (for example, trade name “RINT-TTR” manufactured by Rigaku Corporation) is used. It is possible to employ a method of measuring by X-ray diffraction under the conditions of the Bragg-Brentano optical system.

  In the present invention, when the lanthanum silicate (thin film) is measured by X-ray diffraction (XRD), the peak intensity of the (002) plane and the (001) plane (where l Is a ratio with the peak intensity of other surfaces other than (the ratio (intensity ratio) is [(002) plane peak intensity] / [other plane peak intensity]). The minimum value obtained by calculating the above is 10 or more. Thus, in the lanthanum silicate, the peak of the (002) plane, which is a plane perpendicular to the c-axis, has a peak other than the plane (other than the (00l) plane) at an angle other than perpendicular to the c-axis. It has an intensity of 10 times or more with respect to the other surface (for example, peak of (100) surface, (110) surface, etc.). Such a lanthanum silicate can be said to have a high c-axis orientation from the above strength ratio, and can be said to be a thin film having a sufficiently high orientation. A thin film having a minimum value of the intensity ratio ([(002) plane peak intensity] / [other plane peak intensity]), which is an index of such c-axis orientation, is less than the lower limit, The orientation is low.

  In addition, when the apatite-type lanthanum silicate thin film is formed on the substrate, the peak of the (002) plane is obtained from the viewpoint that the thin film is made of a crystal whose c axis is oriented in a direction highly perpendicular to the substrate. Ratio of intensity to peak intensity of other planes other than (001) plane (where l is an integer of 1 or more) ([(002) plane peak intensity] / [peak of other planes) The minimum value of the intensity]) is more preferably 25 or more, and still more preferably 60 or more. In the present invention, the intensity of the peak of the (002) plane is used as a reference for the peak of the plane (peak of the (002) plane) to indicate the extent that the (002) plane of the thin film is parallel to the substrate. And the ratio of the crystals in the film whose (002) plane is parallel to the substrate, the index of c-axis orientation (thin film is more parallel to the surface of the substrate) This is because it can be suitably used as an index of being a surface. The intensity of the peak on the (002) plane and the intensity of peaks on the other planes other than the (001) plane (where l represents an integer of 1 or more) are X of the crystal structure described above. It can be determined by measuring the lanthanum silicate (thin film) by X-ray diffraction by adopting the same method as that by X-ray diffraction (XRD). That is, the intensity ratio can be obtained by measuring the crystal structure of the lanthanum silicate constituting the lanthanum silicate thin film by X-ray diffraction to obtain the XRD pattern.

  As the apatite-type lanthanum silicate thin film of the present invention, the apatite-type lanthanum silicate precursor thin film of the present invention is baked at a temperature condition of 800 to 1200 ° C. (more preferably 850 to 1200, more preferably 900 to 1200). It is preferable that it is a thin film obtained by this.

  Further, the minimum value of such intensity ratio ([(002) plane peak intensity] / [other plane peak intensity]) is 10 or more (more preferably 25 or more, more preferably 60 or more). From the viewpoint of achieving a sufficiently high c-axis orientation more efficiently, the apatite-type lanthanum silicate precursor thin film of the present invention used for the production of the apatite-type lanthanum silicate thin film is formed on a quartz glass substrate. Alternatively, it is preferably formed on a Si (100) substrate. Thus, when the apatite-type lanthanum silicate thin film of the present invention is manufactured using the precursor thin film formed on the quartz glass substrate or the Si (100) substrate, the surface of the substrate becomes a flat plane. The film having a more uniform and flat surface can be more efficiently produced, the c-axis orientation can be enhanced, and the intensity ratio can be achieved more efficiently. Become.

  Further, in the apatite-type lanthanum silicate thin film of the present invention, the apatite-type lanthanum silicate thin film is laminated on the substrate, and the c-axis of the apatite-type crystal structure in the thin film and the perpendicular of the substrate (surface of the substrate) It is preferable that the average value of the angle formed with a line perpendicular to the angle is 15 ° or less (more preferably 10 ° or less, still more preferably 5 ° or less). When the average value of the angle formed between the c-axis of the apatite-type crystal structure in the thin film and the perpendicular of the substrate (hereinafter, this angle is sometimes simply referred to as “angle A”) exceeds the upper limit. The oxide ion conductivity tends to be low. In addition, such an average value of the angle A is obtained by using a transmission electron microscope (for example, trade name “JEM-2100F” manufactured by JEOL Ltd.) as a measuring device in an arbitrary cross section in the apatite-type lanthanum silicate thin film. Then, under the condition that a single columnar particle is observed in the restricted field squeeze, the restricted field electron diffraction image is measured to obtain the crystal zone axis, and the angle between the perpendicular to the substrate and the crystal zone axis is calculated. Then, it can be obtained by calculating the average value of the angles calculated for any three or more zone axes.

  Furthermore, in the apatite-type lanthanum silicate thin film of the present invention, the apatite-type lanthanum silicate thin film is laminated on a substrate, and is 70% or more (more preferably 80% or more, more preferably 90% or more) of the volume of the thin film. ), The crystal orientation is preferably aligned from one surface of the thin film to the other surface. If the volume ratio of the region where the crystal orientations are aligned is less than the lower limit, the oxide ion conductivity tends to decrease. In addition, the area | region where such crystal orientation is equal can be calculated | required as follows. First, using a scanning electron microscope (for example, trade name “JSM-7000F” manufactured by JEOL Ltd.) equipped with an OIM crystal orientation analyzer (for example, manufactured by TSL Solutions, Inc.), the surface of the thin film is applied. Electron beam backscatter diffraction pattern (EBSD pattern) is obtained by electron beam backscatter diffraction method (acceleration voltage 15 kV, magnification 15000 times, measurement area 5 μm × 5 μm, measurement step 30 nm is adopted), and apatite lanthanum silicate. It is confirmed that the region where the (001) plane showing is 70% or more (more preferably 80% or more, still more preferably 95% or more) of the surface of the film. Next, using a transmission electron microscope (for example, trade name “JEM2100F” manufactured by JEOL Ltd.) as a measuring device, the presence of columnar particles is confirmed under the condition of observing a bright field image, and any two or more The measurement region at a position of 70 nm in the film thickness direction from the surface of the thin film (surface side region: the measurement range is a circle with a radius of 60 nm, and the center of the circle is 70 nm in the film thickness direction from the surface of the thin film. And a measurement region at a position of 70 nm in the film thickness direction from the other surface of the thin film (region on the other surface side: the measurement range is a circle with a radius of 60 nm, and the center of the circle is In this case, a limited-field electron diffraction image is obtained from each surface of the thin film, and the limited-field electron diffraction images on the surface side of the same columnar particle are compared with each other. And the diffraction pattern is Check matches or not, the case where the diffraction pattern of the selected-area electron beam diffraction image is matched in either of the columnar particles can be regarded as the crystal orientation of the columnar grains is uniform. Here, from the measurement result of the electron beam backscatter diffraction pattern (EBSD pattern), the columnar particles are particles that are 70% or more (more preferably 80% or more, more preferably 95% or more) of the same crystal. Can be considered. Therefore, from the measurement result of the electron beam backscatter diffraction pattern (EBSD pattern), it is confirmed that a film is formed of particles made of the same crystal in 70% or more of the surface area, and any two Confirm that the limited-field electron diffraction images in each measurement region (the measurement region on the surface side and the measurement region on the other surface side) in the same columnar particle match for one or more columnar particles. It is confirmed that the crystal orientation is uniform from one surface of the film to the other surface in two or more columnar particles, and in one region of the thin film in a region of 70% or more of the volume of the thin film It can be determined that the crystal orientation is aligned from the surface to the other surface, and the volume ratio is obtained based on this. That is, in any two or more columnar particles, when the crystal orientation is aligned from one surface of the film to the other surface, a region where the (001) plane showing apatite-type lanthanum silicate is confirmed is 70 on the surface of the film. % Or more, it is determined that the crystal orientation is aligned from one surface of the thin film to the other surface in a region of 70% or more of the volume of the thin film.

  When the apatite-type lanthanum silicate precursor thin film of the present invention is fired to prepare the apatite-type lanthanum silicate thin film of the present invention, basically, crystal nuclei are formed on the surface of the thin film during firing. Since crystals can be grown anisotropically in the film thickness direction, the crystal orientation on the surface of the film coincides with the crystal orientation on the other surface of the film. Therefore, by obtaining an electron beam backscatter diffraction pattern (EBSD pattern) and measuring that the area where the (001) plane showing apatite-type lanthanum silicate is confirmed is 70% or more of the surface of the thin film, It can be judged that the crystal is uniformly produced in a region of 70% or more of the surface of the film, and in any two columnar particles, the region in the vicinity of one surface of the thin film and the other surface of the film It is measured whether or not the crystal orientation with the neighboring region is aligned. If the orientation is aligned, one of the films is observed in the entire region where the (001) plane showing the apatite lanthanum silicate is observed. It can be assumed that the crystal orientation is uniform from one surface to the other.

  Thus, in the apatite-type lanthanum silicate thin film of the present invention, the apatite-type lanthanum silicate thin film is laminated on the substrate, and the c-axis of the apatite-type crystal structure in the thin film and the perpendicular of the substrate are formed. It is preferable that the average value of the angles is 15 ° or less, and the crystal orientation is uniform from one surface of the thin film to the other surface in a region of 70% or more of the volume of the thin film. Thus, in the region where the crystal orientation is aligned from one surface of the thin film to the other surface, there is no grain boundary that changes the crystal orientation in the c-axis direction with excellent oxide ion conductivity. Therefore, it becomes possible to obtain more excellent oxide ion conductivity.

  Moreover, in such an apatite type lanthanum silicate thin film of the present invention, the thickness of the thin film is preferably 3000 nm or less. Moreover, as thickness of such a thin film, it is more preferable that it is 50-3000 nm, and it is still more preferable that it is 50-1000 nm. If the thickness of such a thin film is less than the lower limit, the strength tends to decrease and pinholes tend to occur. On the other hand, if the thickness exceeds the upper limit, the oxide ion conductivity tends to decrease. Note that the thickness of such a thin film is at least three or more fields of view (in addition, one field of view includes a region including at least both surfaces of the thin film (if the thin film is formed on the substrate, the cross section The region including the surface of the film from the substrate), the film occupies 40% or more of the vertical length of the field of view, and the width of the film in the field of view is 1.5 times the length of the film thickness, In the field of view, the region including the film is preferable.) In the scanning electron microscope, the cross section of the measurement sample is measured, and the distance between both surfaces of the film in the obtained scanning electron microscope image of each field of view is calculated. Obtained as the film thickness, the average value is adopted. The distance between both surfaces of the film in each field of view is, for example, an approximate straight line (hereinafter, referred to as “first straight line” in some cases) by the least square method with respect to the edge of one surface (one surface) of the film. After drawing, the other surface (the other surface) is referred to as a straight line (hereinafter sometimes referred to as a “second straight line”) parallel to the approximate straight line (first straight line) as described later. ) To obtain the distance between the two straight lines, and the distance between the two straight lines can be measured as the distance between both surfaces of the film. Such a second straight line (straight line to be drawn later) is first formed for each visual field by obtaining the area of the film in the visual field by image processing, the two straight lines, and the edge of the visual field. Draw so that the area of the parallelogram matches. In the case where a thin film is formed on the substrate, first, an approximate straight line is drawn with respect to the substrate surface instead of the first straight line, and the straight line is regarded as the first straight line. As described above, the distance between the two straight lines may be obtained by drawing the second straight line, and the distance between the two straight lines may be measured as the distance between both surfaces of the film. However, the substrate is a silicon substrate (Si substrate) such as a Si (100) substrate or a quartz substrate, and the distance between the concave and convex portions on the surface of the film has a size of 2% or less of the desired film thickness. In this case, instead of the first straight line, a straight line connecting the two intersections of the substrate surface and the edge of the field of view is drawn first, and then the film parallel to the straight line instead of the second straight line. A straight line on the surface is drawn (note that the straight line on the film surface is drawn at a position where the distance is equal to the lowest point of the concave portion on the film surface and the apex of the convex portion on the film surface). The distance between the straight lines may be obtained, and the distance between these straight lines may be measured as the distance between both surfaces of the film. In this way, the distance between both surfaces of the film is obtained in any three or more visual fields, and the averaged value is adopted as the thickness value (film thickness) of the thin film.

The method for producing the apatite-type lanthanum silicate thin film of the present invention is not particularly limited, but the apatite-type lanthanum silicate precursor thin film of the present invention is used to produce the apatite-type lanthanum silicate precursor of the present invention. The composite oxide particles constituting the apatite-type lanthanum silicate precursor thin film are crystallized by firing the body thin film at a temperature of 800 to 1200 ° C. (more preferably 850 to 1200, more preferably 900 to 1200), It is preferable to employ a method of manufacturing by forming a thin film made of lanthanum silicate having a patite type crystal structure. From this point of view, the method for producing the apatite-type lanthanum silicate thin film of the present invention includes a lanthanum salt at a molar ratio of lanthanum to silicon (La: Si) of 4: 3 to 5: 3. A raw material solution containing tetraalkoxysilane and having a pH of 3.5 to 7 is heated under a temperature condition of 350 to 600 ° C. to precipitate composite oxide particles containing lanthanum and silicon as main metal elements. The apatite is a thin film made of an aggregate of the composite oxide particles, and the volume fraction of pore voids having a pore diameter of 16 nm or more is 1% or less with respect to the total volume of the thin film. A step (i) of obtaining a type lanthanum silicate precursor thin film;
A step (ii) of obtaining an apatite-type lanthanum silicate thin film by firing the apatite-type lanthanum silicate precursor thin film at a temperature of 800 to 1200 ° C. (more preferably 850 to 1200, more preferably 900 to 1200);
It is preferable to employ a method comprising: In the method employing such steps (i) and (ii), the apatite-type lanthanum silicate thin film of the present invention can be obtained by a simple method such as heating of the raw material solution and subsequent firing of the precursor thin film. Further, it is possible to produce a lanthanum silicate thin film having an apatite-type crystal structure with high productivity and sufficiently efficiently without requiring separate provision of expensive equipment.

  Such step (i) is the same method as the method for producing the apatite-type lanthanum silicate precursor thin film of the present invention (the preferred conditions are also the same). In addition, when the suitable temperature condition for firing the apatite-type lanthanum silicate thin film in such step (ii) is less than the lower limit, crystallization takes a very long time, and the thin film is efficiently produced. On the other hand, if the upper limit is exceeded, expensive equipment is required, and the cost tends to increase. In addition, by using the apatite type lanthanum silicate precursor thin film of the present invention, the crystal growth can be performed sufficiently efficiently at the time of firing, and even at a relatively low firing temperature of 800 to 1200 ° C. Thus, the apatite-type lanthanum silicate thin film of the present invention can be produced sufficiently efficiently as a film (alignment film) having a sufficiently high orientation.

  In addition, the atmospheric conditions for such firing are not particularly limited, and may be atmospheric conditions (in the atmosphere) from the viewpoint of reducing the manufacturing cost and sufficient oxidation of the film. Thus, by using the apatite-type lanthanum silicate precursor thin film of the present invention, the apatite-type lanthanum silicate thin film of the present invention can be efficiently produced by a simple process such as firing in the atmosphere.

  In this way, by using the apatite-type lanthanum silicate precursor thin film of the present invention and firing it at a temperature of 800 to 1200 ° C., the (002) plane peak intensity and (001) The minimum of the ratio ([(002) plane peak intensity] / [other plane peak intensity]) with respect to the peak intensity of other planes other than the plane (where l represents an integer of 1 or more) A thin film made of lanthanum silicate having an apatite type crystal structure with sufficiently high c-axis orientation such that the value is 10 or more can be obtained efficiently. Thus, the apatite-type lanthanum silicate precursor thin film of the present invention is baked at a temperature of 800 to 1200 ° C., whereby the apatite-type lanthanum silicate thin film of the present invention having sufficiently high c-axis orientation can be produced more efficiently. It becomes possible to do. This is because the apatite-type lanthanum silicate precursor thin film of the present invention has a sufficiently small volume fraction of 1% or less with respect to the entire film having large pores of 16 nm or more, so that the relatively low temperature of 800 to 1200 ° C. Even when fired under the above temperature conditions, the ratio of large pores that inhibit the growth of crystals is small between the films made of composite oxide particles that are precursors of lanthanum silicate, and the crystals are grown more efficiently. In the first place, crystal nuclei are formed on the surface of the thin film at the time of firing, and the crystal can be grown anisotropically in the film thickness direction. Therefore, the intensity of the (002) plane peak, Ratio ([(002) plane peak intensity] / [other plane peak intensity] with respect to the peak intensity of other planes other than the (00l) plane (where l represents an integer of 1 or more) ) The present inventors speculate that this is because a thin film made of lanthanum silicate having an apatite-type crystal structure with sufficiently high c-axis orientation such that the minimum value is 10 or more can be formed efficiently. To do. Thus, the apatite type lanthanum silicate precursor thin film of the present invention can be used to efficiently form the apatite type lanthanum silicate thin film of the present invention.

In general, lanthanum silicate having an apatite type crystal structure has a large oxide ion conductivity in the c-axis direction of the unit cell. This is because the crystal system of a compound having a crystal structure of an apatite type structure usually belongs to the hexagonal system, and the oxide ions (O ²⁻ ) existing at the 2a site move in the crystal structure. It is assumed that the oxide ion conduction occurs and the oxide ion conductivity along the moving direction increases. That is, in the apatite structure belonging to the hexagonal system, it is considered that oxide ion conduction is developed as the oxide ions (O ²⁻ ) move along the c-axis, and the crystal is oriented in the c-axis direction. Thus, it is considered that the oxide ion conductivity is increased by the orientation.

  Here, the apatite-type lanthanum silicate thin film of the present invention has a (002) plane peak intensity (adopted as an index of peak intensity of a plane perpendicular to the c-axis (crystal plane)) and a (00l) plane (provided that l Is an integer greater than or equal to 1. Ratio to the intensity of the peak of other planes (crystal planes other than the crystal plane perpendicular to the c-axis) (intensity ratio: [peak intensity of (002) plane] / [ A thin film made of apatite-type lanthanum silicate with the c-axis sufficiently oriented in the direction perpendicular to the film surface so that the minimum value of the peak intensity of the other surface is 10 or more (in such a thin film) The film surface is sufficiently parallel to the substrate. Therefore, the apatite-type lanthanum silicate thin film of the present invention exhibits a higher ionic conductivity in the film thickness direction due to its orientation, and an oxide ion conductor (for example, a solid electrolyte thin film) for conducting ions in the film thickness direction. It can be suitably used as. Such an apatite-type lanthanum silicate thin film is sufficiently high in the c-axis direction (film thickness direction) even under relatively low temperature conditions (about 500 ° C.) due to its sufficiently high orientation. For example, when this is used for a solid oxide fuel cell, a battery operating at a lower temperature can be obtained. Thus, the apatite-type lanthanum silicate thin film of the present invention can be a solid electrolyte thin film showing high ionic conductivity in the film thickness direction due to orientation, and by using this for a solid oxide fuel cell, the battery Enables low temperature operation.

  In addition, as described above, the apatite-type lanthanum silicate thin film of the present invention has a sufficiently uniform crystal oriented so that the c-axis is parallel to the film thickness direction (c-axis is perpendicular to the surface of the substrate). Since the thin film exhibits sufficiently high ion conductivity in the c-axis direction (film thickness direction) due to its orientation, for example, for a solid oxide fuel cell as described above In addition to its use as a solid electrolyte membrane, it can be suitably used for applications such as oxygen separation membranes, exhaust purification devices, and oxygen sensors. Thus, the apatite-type lanthanum silicate thin film of the present invention is particularly useful as a thin film used for a solid electrolyte membrane, an oxygen separation membrane, an exhaust purification device, an oxygen sensor and the like for a solid oxide fuel cell.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
After dissolving 1.371 g (0.3166 mmol) of lanthanum nitrate hexahydrate (La (NO ₃ ) ₃ .6H ₂ O) in 10 mL of water having a pH of 7 at room temperature (25 ° C.) Furthermore, 10 mL of ethanol was added and mixed to obtain a mixed solution. Next, under a temperature condition of room temperature (25 ° C.), 0.417 g (2 mmol) of tetraethoxysilane (TEOS) is added to the mixed solution, and the mixture is stirred with a magnetic stirrer for 5 minutes, thereby tetraethoxysilane (TEOS). Was dissolved to obtain a raw material solution (pH: 4.8).

  Using the raw material solution thus obtained as a coating solution as it is, on one surface ((100) surface) of the Si (100) substrate (length: 35, width: 35, thickness: 0.5 mm), The said coating liquid (the said raw material solution) was apply | coated with the spin coat method of rotation speed: 2000rpm and time: 20s (application | coating process). Next, the coating film formed by applying the raw material solution was subjected to a heat treatment for 2 minutes under a temperature condition of 400 ° C. to deposit particles on the substrate (heat treatment step). Next, the substrate on which the particles were deposited was cooled to room temperature (25 ° C.) (cooling step). Thereafter, the coating step, the heat treatment step, and the cooling step are sequentially performed on one surface (surface of the substrate after cooling) on the substrate on which the coating step, the heat treatment step, and the cooling step are performed. Repeatedly, a thin film composed of the aggregate of the particles was obtained (the number of times each step was performed was 10 times). In addition, after preparing each raw material solution used for such each application | coating process on the conditions of room temperature (25 degreeC) so that hydrolysis and superposition | polymerization of TEOS may not advance in a solution, before apply | coating to a board | substrate, Used as is within 2 hours.

<XRD measurement>
XRD measurement of the thin film formed on the substrate as described above using an X-ray diffraction (XRD) apparatus (trade name “RINT-TTR” manufactured by Rigaku Corporation) under the conditions of the Bragg-Brentano optical system. Went.

  FIG. 1 shows an XRD pattern of a thin film. As is apparent from the XRD pattern shown in FIG. 1, since halos (peaks having a half-value width of 5 ° or more) were observed when 2θ was around 28 ° and around 45 °, the particles forming the thin film were lanthanum It was found that the oxide and silicon oxide were partly dissolved, and were composed of a composite oxide containing lanthanum and silicon. Further, broad peaks (halo) are confirmed around 28 ° and 45 ° from the XRD pattern shown in FIG. 1, and no sharp peak (half-value width of 2 ° or less) is confirmed. Thus, the obtained thin film is formed. The composite oxide was confirmed to be amorphous.

<SEM measurement>
The thin film formed on the substrate as described above was measured with a scanning electron microscope (SEM: trade name “S-5500” manufactured by Hitachi High-Technologies Corporation). FIG. 2 shows a scanning electron micrograph (cross-sectional SEM image of the thin film) of the cross section of the thin film formed on the substrate.

  As is clear from the SEM image shown in FIG. 2, it was confirmed that the thin film formed on the substrate was composed of an aggregate of fine particles of a complex oxide containing lanthanum and silicon. In addition, the film thickness (average value of the thickness) of such a thin film is measured by a scanning electron microscope as described above (arbitrary three visual fields [the range of each measurement visual field includes at least both surfaces of the thin film, respectively). The film occupies 80% or more of the vertical length of the visual field, and the lateral width of the film in the visual field is 1.5 times or more (2.2 times) the film thickness. , The region including the film was measured), and was found to be 270 nm (in addition, as a method for measuring the thickness of the thin film, the substrate was a silicon substrate (Si substrate), The measurement method described above was employed when the distance from the convex portion was 2% or less of the desired film thickness.

  In addition, the cross section of the thin film formed on the substrate as described above was measured with a scanning electron microscope (SEM: trade name “S-5500” manufactured by Hitachi High-Technologies Corporation), and the size of one field of view was 475 nm in length, The ratio of pores having pore diameters of 16 nm or more with respect to the entire film in a cross section in each field of view was measured at a horizontal of 635 nm ([volume of void] / [volume of entire film] × 100: unit) %) Were obtained and averaged, and the average value was 0.3%. Since the volume is obtained by integration of the surface, the average value can be assumed to be a ratio of the volume of the voids of the pores having a pore diameter of 16 nm or more to the total volume of the thin film. In this example, It was found that the volume fraction of pore voids having a pore diameter of 16 nm or more was 0.3% with respect to the total volume of the thin film.

<Measurement by small angle X-ray scattering method>
Using an X-ray diffraction (XRD) apparatus (trade name “NANOSTAR” manufactured by Burker, etc.) with an incident angle of 0.24 ° and a distance of 1077 mm between the thin film and the detector, An X-ray scattering pattern (scattering intensity pattern) is obtained, and then a spherical sky having a size distribution using analysis software (software “Irena” developed by J. Ilavsky of Argonne National Laboratory [Argonne National Laboratory]) By fitting with a pore model, the relative volume ratio (volume distribution: f (R)) of the pores was measured automatically. A graph showing the relationship between the pore size (radius) in the thin film obtained by such measurement and the relative volume fraction of the pores (volume distribution: f (R)) is shown in FIG. As is clear from the results of the XRD measurement and SEM measurement as described above, in Example 1, the amorphous composite oxide containing lanthanum and silicon (La for all metal elements in the composite oxide). The total volume of Si and Si is 100 at% from the charged amount.) And the volume fraction of pore voids having a pore diameter (diameter) of 16 nm or more. It was found that a thin film (ratio to the total volume of the thin film) was 0.3% was obtained.

(Example 2)
The thin film obtained in Example 1 (thin film formed on the substrate) was fired in air at a temperature of 900 ° C. for 2 hours to crystallize the particles constituting the thin film. A thin film was obtained.

XRD measurement was performed on the fired thin film thus obtained in the same manner as in Example 1. FIG. 4 shows the XRD pattern of the fired thin film as such a measurement result. As is clear from the results of such XRD measurement (including the results shown in FIG. 4), the peak of the JCPDS card 49-0443 and the peak having the same angle 2θ were confirmed in the XRD pattern, and the thin film after firing Was found to be composed of lanthanum silicate having an apatite-type crystal structure with a space group of P6 ₃ / m. Further, as is apparent from the XRD pattern shown in FIG. 4, the (001) plane peak appears strongly in the XRD pattern, and the c-axis is sufficiently oriented in the direction perpendicular to the substrate, so that it is sufficiently advanced. It was confirmed that there was orientation. As is clear from the XRD pattern shown in FIG. 4, the ratio of the peak intensity of the (002) plane to the peak intensity of other planes other than the (001) plane ([peak intensity of (002) plane] / [ The minimum value of the peak intensity of other surfaces other than the (00l) surface]) was 62.5. From these strength ratio results, in the thin film after firing (thin film made of lanthanum silicate having an apatite type crystal structure: apatite type lanthanum silicate thin film), the c-axis is sufficiently oriented in the direction perpendicular to the substrate. It was confirmed that the film surface was sufficiently parallel to the surface of the substrate.

  Moreover, when the SEM measurement was performed like Example 1 with respect to the thin film after baking obtained in this way, it was confirmed that a film thickness (average film thickness) is 240 nm.

<Measurement by backscattered electron diffraction method>
Using a scanning electron microscope (SEM: trade name “JSM-7000F” manufactured by JEOL Ltd.) equipped with an OIM crystal orientation diffractometer (manufactured by TSI Solutions), an acceleration voltage of 15 kV, a magnification of 15000 times, a measurement region of 5 μm × A backscattered electron diffraction image (electron beam backscattering diffraction pattern: EBSD pattern) of the surface of the thin film obtained in Example 2 was obtained by an electron beam backscattering diffraction method employing conditions of 5 μm and a measurement step of 30 nm. From the results of such backscattered electron diffraction images, it was confirmed that the surface of the thin film had a (001) plane in the region of 80% of the thin film area indicating c-axis oriented apatite-type lanthanum silicate. It was done.

<TEM measurement>
The cross section of the thin film formed on the substrate as described above was measured with a transmission electron microscope (TEM: trade name “JEM-2100F” manufactured by JEOL Ltd.). The obtained transmission electron micrograph is shown in FIG. From the results shown in FIG. 5, in the thin film, the width (the diameter of the smallest circle in contact with the two sides perpendicular to the substrate drawn on the outer edge of the columnar particles) is about 100 to 200 nm, and the length (the length in the film thickness direction). ) Was confirmed to be aligned with columnar particles of about 240 nm.

  Taking into account the measurement result by the backscattered electron diffraction method, it was found that the columnar particles confirmed by the TEM measurement were particles made of c-axis oriented apatite-type lanthanum silicate crystals.

  Further, with respect to any two columnar particles constituting the thin film confirmed by the TEM measurement, a measurement region at a position of 70 nm in the film thickness direction from the surface of the thin film, respectively, using the transmission electron microscope. (Surface side region: The measurement range is a circle with a radius of 60 nm, and the center of the circle is positioned 70 nm in the film thickness direction from the surface of the thin film) and the other surface of the thin film (on the substrate side) Measurement area at a position of 70 nm from the surface to the film thickness direction (area on the substrate side: the measurement range is a circle with a radius of 60 nm, and the center of the circle is located at a position of 70 nm from the surface of the thin film in the film thickness direction.) In each of the above, a limited-field electron diffraction image was obtained. In addition, regarding the same single columnar particle in FIG. 5, the limited field electron beam in the measurement region (measurement region at a position 70 nm from the surface of the thin film in the film thickness direction) in the region A on the surface side indicated by the dotted line A diffraction image is shown in FIG. 6, and a limited-field electron beam in the measurement region (measurement region at a position of 70 nm in the film thickness direction from the other surface of the thin film) in the region B on the substrate side indicated by a dotted line in FIG. A diffraction image is shown in FIG.

  As is clear from the results shown in FIGS. 6 and 7, the limited-field electron diffraction image of the columnar particles near the substrate (substrate-side measurement region) and the limited-field electron beam near the surface (surface-side measurement region). It was confirmed that the diffraction images matched. From these results, it was confirmed that the measured columnar particles had the same crystal orientation from the upper end to the lower end. Similarly, in any other columnar particles, a limited-field electron diffraction image near the substrate of the columnar particles (measurement region on the substrate side at a position of 70 nm in the film thickness direction from the surface of the thin film) It was confirmed that the limited-field electron beam diffraction image in the vicinity of the surface (the measurement region on the surface side at a position of 70 nm in the film thickness direction from the surface of the thin film) coincided and the crystal orientation was aligned from the upper end to the lower end. From these results, it can be considered that each columnar particle has a uniform crystal orientation from the upper end to the lower end.

  Considering the measurement result of the limited field electron diffraction image and the measurement result by the backscattering electron diffraction method, in the region of 80% of the volume of the thin film, the surface of the thin film is It was found that the crystal orientation was aligned up to the surface.

  In addition, by using the transmission electron microscope (trade name “JEM-2100F” manufactured by JEOL Ltd.), single columnar particles are observed in the limited field of view in an arbitrary cross section in the thin film. Under the conditions, the limited-field electron diffraction image is measured to obtain the zone axis, and the angle between the perpendicular to the substrate and the zone axis is calculated, and at any 3 points (any 3 points of crystal By calculating the average value of the calculated angles (in the band axis), the average value of the angles formed by the c-axis of the apatite type crystal structure (crystals forming the columnar particles) in the thin film and the normal of the substrate Was found to be 3.9 °. From these results, it was found that the c-axis was oriented in a direction perpendicular to the substrate at a sufficiently high level.

(Comparative Example 1)
Instead of using the raw material solution as it is as the coating solution, after preparing the raw material solution, the solution is subjected to a refluxing step of refluxing at a temperature condition of 70 ° C. for 24 hours, and the obtained solution after refluxing A thin film made of an aggregate of particles on a substrate was obtained in the same manner as in Example 1 except that was used as the coating liquid.

  The XRD measurement was performed on the thin film thus obtained in Comparative Example 1 in the same manner as in Example 1. As a result, the particles forming the thin film were partially lanthanum oxide and silicon oxide. It was found to be composed of a solid solution and composed of a complex oxide containing lanthanum and silicon. In addition, SEM measurement was performed on the thin film obtained in Comparative Example 1 in the same manner as in Example 1. FIG. 8 shows a scanning electron micrograph (cross-sectional SEM image of the thin film) of the cross section of the thin film formed on the substrate in Comparative Example 1. As is clear from the results shown in FIG. 8, in the thin film obtained in Comparative Example 1, coarse particles were scattered, and many coarse pores having a pore diameter of 16 nm or more were confirmed.

  Similarly to Example 1, the cross section of the thin film obtained in Comparative Example 1 was also measured with a scanning electron microscope (SEM: trade name “S-5500” manufactured by Hitachi High-Technologies Corporation). The ratio of the pores having pore diameters of 16 nm or more to the entire film in the cross section in each field ([volume of void] / [volume of entire film]) × 100: unit%) was obtained and averaged, and the average value was 4.4%. From these results, the thin film obtained in Comparative Example 1 was found to have a volume fraction of pore voids having a pore diameter of 16 nm or more of 4.4% with respect to the total volume of the thin film.

  Further, the thin film obtained in Comparative Example 1 was measured by the small angle X-ray scattering method in the same manner as in Example 1, and the relative volume fraction of pores (volume distribution: f (R)) Asked. A graph showing the relationship between the pore size in the thin film and the relative volume fraction of the pores (volume distribution: f (R)) obtained by such measurement is shown in FIG.

  The results of the volume distribution obtained by the small angle X-ray scattering method of the thin film obtained in Example 1 (FIG. 3) and the volume distribution of the thin film obtained in Comparative Example 1 obtained by the small angle X-ray scattering method. The results of FIG. 9 (FIG. 9) were compared, the area of pores having a pore diameter (diameter) of 16 nm or more was determined from the volume distribution graph, and the area ratio was determined. The area of the pores of 16 nm or more was 11% ({[Example 1 (the area)] / [Comparative Example 1 (the above) Area)]} × 100). Thus, from the area ratio of the volume distribution graph obtained by the small-angle X-ray scattering method, the thin film obtained in Example 1 has a sufficiently low ratio of pores having a size of 16 nm or more as compared with Comparative Example 1. It was confirmed that

(Comparative Example 2)
After firing the thin film obtained in Comparative Example 1 (thin film formed on the substrate) in air at 900 ° C. for 2 hours to crystallize the particles constituting the thin film, after firing A thin film was obtained.

XRD measurement was performed on the fired thin film thus obtained in the same manner as in Example 1. FIG. 10 shows the XRD pattern of the thin film after firing as such a measurement result. As is clear from the results of such XRD measurement (including the results shown in FIG. 10), the peak of the JCPDS card 49-0443 and the peak having the same angle 2θ were confirmed in the XRD pattern, and the thin film after firing Was found to be composed of lanthanum silicate having an apatite type crystal structure with a space group of P6 ₃ / m. However, as is clear from the results shown in FIG. 10, in the XRD pattern, in addition to the (001) plane peak, a large number of strong peaks were confirmed. The (002) plane peak intensity and the (001) plane The minimum value of the ratio of the peak intensities of other surfaces ([peak intensity of (002) plane] / [peak intensities of other surfaces other than (001) plane]) was 1.1.

[Contrast results of thin films obtained in Example 2 and Comparative Example 2]
In Example 2, in the obtained apatite-type lanthanum silicate thin film, the intensity ratio between the peak intensity of the (002) plane and the peak intensity of other planes other than the (001) plane (the peak intensity of the [(002) plane) ] / [Peak intensity of other planes other than (001) plane]) is 62.5, and a crystal whose c-axis is perpendicular to the substrate is sufficiently uniform. As can be seen, it was found that the orientation was sufficiently high in the direction perpendicular to the substrate. From these results, the apatite-type lanthanum silicate thin film (Example 2) of the present invention is a thin film in which the c-axis is sufficiently oriented in the direction perpendicular to the substrate, and the crystal structure of the lanthanum silicate constituting the thin film and its From the orientation, it can be seen that the ion conductivity is sufficiently high in the c-axis direction (film thickness direction). In contrast, the apatite-type lanthanum silicate thin film obtained in Comparative Example 2 had a strength ratio of 1.1 and did not exhibit a sufficiently high degree of orientation in the direction perpendicular to the substrate.

  From the results obtained from FIG. 3 and FIG. 9 described above, as described above, the area of pores of 16 nm or more in the volume distribution graph of Example 1 is 16 nm of the volume distribution graph of Comparative Example 1. It was confirmed that it was about 11% of the area of the above pores. In addition, the thin film obtained in Example 1 had a pore volume fraction (ratio to the total volume of the thin film) of 0.3% of the pores having a pore diameter (diameter) of 16 nm or more. The thin film obtained in Comparative Example 1 had a void volume fraction of 4.4%. Considering these results together with the result of the intensity ratio, in Comparative Example 2, it is inferred that the growth of crystals in a certain direction was inhibited during crystallization by coarse pores. be able to.

(Example 3)
A thin film made of an aggregate of particles on a substrate in the same manner as in Example 1 except that the pH of the raw material solution was adjusted (changed) to 3.7 by adding an appropriate amount of nitric acid during preparation of the raw material solution. Got. Thus, when the XRD measurement was performed like Example 1 with respect to the thin film obtained in Example 3, this thin film should consist of an amorphous complex oxide containing lanthanum and silicon. Was confirmed. Moreover, when SEM measurement was performed on the thin film in the same manner as in Example 1, the thin film formed on the substrate was composed of an aggregate of fine particles of a complex oxide containing lanthanum and silicon. It was confirmed that. For the thin film obtained in Example 3, the volume fraction of pore voids (ratio to the total volume of the thin film) having a pore diameter (diameter) of 16 nm or more was determined in the same manner as in Example 1. The volume fraction was found to be 0.9%.

Example 4
After firing the thin film obtained in Example 3 (thin film formed on the substrate) in air at a temperature of 900 ° C. for 2 hours to crystallize the particles constituting the thin film, A thin film was obtained.

XRD measurement was performed on the fired thin film thus obtained in the same manner as in Example 1. FIG. 11 shows an XRD pattern of the fired thin film as such a measurement result. As is clear from the results of such XRD measurement (including the results shown in FIG. 11), the peak of the JCPDS card 49-0443 and the peak at the angle 2θ are confirmed in the XRD pattern, and the thin film after firing Was found to be composed of lanthanum silicate having an apatite-type crystal structure with a space group of P6 ₃ / m. In addition, as apparent from the XRD pattern shown in FIG. 11, the fired thin film has a (001) plane peak sufficiently strong in the XRD pattern, and the c-axis is sufficiently oriented in the direction perpendicular to the substrate. It was confirmed that there was a sufficiently high degree of orientation. Further, from the XRD pattern shown in FIG. 11, the ratio of the peak intensity of the (002) plane to the peak intensity of other planes other than the (001) plane ([peak intensity of [(002) plane] / [other than (001) plane) The minimum value of the peak intensity of the other surface]) was 26.8. From the result of such an intensity ratio, it was confirmed that the peak intensity of the (001) plane was sufficiently large, and in the thin film after firing (thin film made of lanthanum silicate having an apatite type crystal structure: apatite type lanthanum silicate thin film) It was confirmed that the c-axis was sufficiently oriented in the direction perpendicular to the substrate.

(Comparative Example 3)
A thin film composed of an aggregate of particles on a substrate was prepared in the same manner as in Example 1 except that nitric acid was added during preparation of the raw material solution to adjust (change) the pH of the raw material solution to 2.2. Obtained. The XRD measurement was performed on the thin film thus obtained in Comparative Example 3 in the same manner as in Example 1. As a result, the thin film was composed of an amorphous complex oxide containing lanthanum and silicon. Was confirmed. Further, SEM measurement was performed on the thin film in the same manner as in Example 1. FIG. 12 shows a scanning electron micrograph (cross-sectional SEM image of the thin film) of the cross section of the thin film obtained in Comparative Example 3. As is clear from the results of such SEM measurement (FIG. 12 and the like), it was confirmed that the thin film formed on the substrate was composed of an aggregate of composite oxide particles containing lanthanum and silicon. In addition, a large number of coarse pores having a pore diameter of 16 nm or more were confirmed. Further, for the thin film obtained in Comparative Example 3, the volume fraction of pore voids (ratio to the total volume of the thin film) having a pore diameter (diameter) of 16 nm or more was determined in the same manner as in Example 1. The volume fraction was found to be 11.1%.

(Comparative Example 4)
After firing the thin film obtained in Comparative Example 3 (thin film formed on the substrate) in air at a temperature condition of 900 ° C. for 2 hours, the particles constituting the thin film are crystallized. A thin film was obtained.

XRD measurement was performed on the fired thin film thus obtained in the same manner as in Example 1. FIG. 13 shows an XRD pattern of the thin film after firing as such a measurement result. As is clear from the results of such XRD measurement (including the results shown in FIG. 13), the peak of the JCPDS card 49-0443 and the peak having the same angle 2θ were confirmed in the XRD pattern, and the thin film after firing Was found to be composed of lanthanum silicate having an apatite type crystal structure with a space group of P6 ₃ / m. However, as is clear from the results shown in FIG. 13, in the XRD pattern, in addition to the (001) plane peak, a large number of strong peaks were confirmed. The (002) plane peak intensity and the (001) plane The minimum value of the ratio of the peak intensities of other surfaces ([peak intensity of (002) plane] / [peak intensities of other surfaces other than (001) plane)) was 0.5. As described above, the thin film obtained in Comparative Example 4 had a small (001) plane peak intensity ratio and did not have a sufficiently high degree of orientation.

[Contrast results of thin films obtained in Example 4 and Comparative Example 4]
In Example 4, in the obtained apatite-type lanthanum silicate thin film, the intensity ratio ([peak intensity of (002) plane] / [peak intensity of other planes other than (001) plane)) was 26.8. Thus, it was found that crystals having a c-axis perpendicular to the substrate were formed sufficiently uniformly, and a sufficiently high orientation was exhibited in the direction perpendicular to the substrate. From these results, the apatite-type lanthanum silicate thin film (Example 4) of the present invention is a thin film in which the c-axis is sufficiently oriented in the direction perpendicular to the substrate, and the crystal structure of the lanthanum silicate constituting the thin film and its From the orientation, it can be seen that the ion conductivity is sufficiently high in the c-axis direction (film thickness direction). In contrast, the apatite-type lanthanum silicate thin film obtained in Comparative Example 4 had a strength ratio of 0.5 and did not exhibit a sufficiently high degree of orientation in the direction perpendicular to the substrate.

  When the preparation methods of the apatite-type lanthanum silicate thin films obtained in Example 4 and Comparative Example 4 are compared, a thin film before firing (thin films obtained in Example 3 and Comparative Example 3) is produced. In the case where only the pH of the raw material solution used is different and the condition that the pH is 2.2 is adopted (Comparative Example 3), the thin film exhibits sufficiently high orientation in the direction perpendicular to the substrate after firing. It was found that could not be obtained. In the case of using a raw material solution having a pH of less than 3.5 based on the results of the volume fraction of pore voids where the pore diameter of the thin film obtained in Example 3 and Comparative Example 3 is 16 nm or more In this case, the ratio of the volume of the pores having a pore diameter of 16 nm or more to the total volume of the film exceeds 1%, and it is assumed that a thin film having a sufficiently high degree of orientation cannot be obtained.

  As described above, according to the present invention, an apatite-type lanthanum silicate precursor that can be used for efficiently producing a lanthanum silicate thin film having an apatite-type crystal structure and sufficiently high c-axis orientation. A thin film of apatite, a method for producing an apatite lanthanum silicate precursor thin film that enables efficient and reliable production of such apatite lanthanum silicate precursor thin film, and growth of crystals Providing an apatite-type lanthanum silicate thin film capable of sufficiently orienting the c-axis in a direction perpendicular to the surface of the substrate used when the substrate is used, and having a sufficiently high c-axis orientation; Is possible.

  Since the apatite-type lanthanum silicate precursor thin film of the present invention can produce an apatite-type lanthanum silicate thin film at a relatively low firing temperature, a solid electrolyte membrane for an oxide fuel cell, an oxygen separation membrane, and exhaust purification It is particularly useful as a material for producing a lanthanum silicate thin film having an apatite type crystal structure for use in devices, oxygen sensors and the like. In addition, since the apatite-type lanthanum silicate thin film of the present invention is particularly excellent in ion conductivity in the c-axis direction, the solid electrolyte membrane, the oxygen separation membrane, the exhaust purification device, the oxygen purification device for the solid oxide fuel cell, the oxygen It is particularly useful as a thin film used for sensors and the like.

Claims (6)

  It is a thin film composed of an aggregate of composite oxide particles containing lanthanum and silicon as main metal elements, and the volume fraction of pore voids having a pore diameter of 16 nm or more is smaller than the total volume of the thin film. 1% or less of an apatite type lanthanum silicate precursor thin film.   The apatite-type lanthanum silicate precursor thin film according to claim 1, wherein the composite oxide particles are made of an amorphous oxide.   The apatite-type lanthanum silicate precursor thin film according to claim 1 or 2, wherein the thin film has a thickness of 50 to 3000 nm. A raw material solution containing a lanthanum salt and tetraalkoxysilane at a ratio of the lanthanum to silicon molar ratio (La: Si) of 4: 3 to 5: 3 and having a pH of 3.5 to 7 is 350 to By heating at 600 ° C. and precipitating composite oxide particles containing lanthanum and silicon as main metal elements,
An apatite-type lanthanum silicate precursor, which is a thin film composed of an aggregate of the composite oxide particles, and has a volume fraction of pore voids having a pore diameter of 16 nm or more with respect to the total volume of the thin film A method for producing an apatite-type lanthanum silicate precursor thin film, characterized in that a body thin film is obtained. It is composed of lanthanum silicate containing lanthanum and silicon as main metal elements and having an apatite type crystal structure,
When the lanthanum silicate is measured by X-ray diffraction, the peak intensity of the (002) plane and the peak intensity of other planes other than the (001) plane (where l is an integer of 1 or more) The minimum ratio is 10 or more,
Apatite-type lanthanum silicate thin film characterized by The apatite-type lanthanum silicate thin film is laminated on a substrate,
The average angle formed by the c-axis of the apatite-type crystal structure in the thin film and the normal of the substrate is 15 ° or less, and
The crystal orientation is aligned from one surface of the thin film to the other surface in a region of 70% or more of the volume of the thin film;
The apatite-type lanthanum silicate thin film according to claim 5.