WO2010064686A1

WO2010064686A1 - Dielectric compound and manufacturing method thereof

Info

Publication number: WO2010064686A1
Application number: PCT/JP2009/070323
Authority: WO
Inventors: 達生藤井; 潤高田; 直池田; 真中西
Original assignee: 国立大学法人岡山大学
Priority date: 2008-12-03
Filing date: 2009-12-03
Publication date: 2010-06-10
Also published as: JPWO2010064686A1; JP5688733B2

Abstract

Provided are a dielectric compound and a method for manufacturing said compound with which dielectric compounds such as RFe₂O₄ can be efficiently synthesized. In the manufacture of a dielectric compound which is represented by (RMbO_3- _δ)_n(MaO)_m and has a stratified triangular lattice structure, a compound containing R as the dielectric compound starting material, a compound containing Ma, and a compound containing Mb are mixed in order to prepare a starting material solution containing each of the elements, namely, R, Ma, and Mb (S101, preparation step); and a solid precursor of the dielectric compound is created from the starting material solution using a liquid phase method, such as coprecipitation (S102, liquid phase synthesis step). Then, the obtained solid precursor is heated at a prescribed calcination temperature in order to obtain a dielectric compound powder (S104, calcination step).

Description

Dielectric compound and manufacturing method thereof

The present invention relates to a dielectric compound having a composition represented by (RMbO _3-δ ) _n (MaO) _m and having a layered triangular lattice structure, and a method for producing the same.

In recent years, a layered triangular lattice compound typified by RFe ₂ O ₄ has attracted attention as a substance that exhibits dielectric properties on a principle different from that of conventional dielectrics. For example, the crystal of the compound RFe ₂ O ₄ has a stacked structure in which triangular lattices each composed of R, Fe, and O are stacked in layers in the c-axis direction (for example, Patent Document 1, Non-Patent Document 1, 2).

The above-mentioned layered triangular lattice structure of RFe ₂ O ₄ includes a structure in which two triangular lattice layers composed of Fe—O are stacked, and such a crystal structure depends on the geometric characteristics of the triangle. It plays the main role in the expression mechanism of physical properties characteristic of RFe ₂ O ₄ . Specifically, the multilayer structure of the triangular lattice layer of Fe-O, and the charge number of Fe in the layer of the other hand, is the charge number of Fe in the other layer, while the Fe ²⁺ is large, on the other hand As Fe ³⁺ increases, they do not match.

In addition, in this structure, when ^viewed from the average charge number Fe ^2.5+ of Fe, Fe ²⁺ has a role as an excessive negative charge of electrons, and Fe ³⁺ has a role of a positive charge with missing electrons. Therefore, a dipole-like electron arrangement and an electron density distribution are formed by the ordered arrangement structure of Fe ²⁺ and Fe ³⁺ and the deviation of the arrangement. In RFe ₂ O ₄ , ferroelectricity appears due to such an electron dipole structure. Further, when considering (RMbO ₃ ) _n (MaO) _m more generally, it has the same characteristic as RFe ₂ O ₄ due to the structure in which two triangular lattice layers composed of Ma—O or Mb—O are stacked. Physical properties are expressed.

JP 2007-223886 A

The synthesis of the dielectric compound RFe ₂ O ₄ described above has been conventionally performed using a solid phase reaction method (see Non-Patent Documents 3 to 5). However, in the synthesis by such a solid phase reaction method, since the reaction rate is slow, heating and baking are required for at least several hours, usually 12 hours or more. In this case, since the synthesis time becomes long, there is a problem that synthesis of RFe ₂ O ₄ cannot be performed efficiently.

Moreover, in the synthesis by the conventional solid phase reaction method, the synthesis is performed at a high temperature of 1100 ° C. or more, for example. When the synthesis is performed under such conditions, there is a problem that the raw material powder is sintered and grain-grown during firing to produce coarse grains. With such coarse particles, when RFe ₂ O ₄ is used as a material for an electronic component or the like, its formability, workability, and the like are inferior. Further, in the synthesis at a high temperature and for a long time as described above, energy consumption during synthesis is increased, and there is a problem in cost. Such a problem generally occurs similarly for the dielectric compound (RMbO ₃ ) _n (MaO) _m .

The present invention has been made to solve the above problems, and provides a method for producing a dielectric compound capable of efficiently synthesizing a dielectric compound such as RFe ₂ O ₄ having a layered triangular lattice structure. The purpose is to provide.

In order to achieve such an object, the dielectric compound manufacturing method according to the present invention has a composition of (RMbO _3-δ ) _n (MaO) _m (R is In, Sc, Y, Dy, Ho, Er). , Tm, Yb, Lu, Ti, Ca, Sr, Ce, Sn, Hf, at least one element, Ma, Mb is Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, A dielectric having a layered triangular lattice structure represented by at least one element selected from Cd with duplication allowed, n is an integer of 1 or more, m is an integer of 0 or more, and δ is a real number of 0 to 0.2. a method of manufacturing a body compound, (1) a dielectric compound _{_{(RMbO 3-δ) n (}} MaO) compounds containing R which is a raw material of _m, compounds containing Ma, and a mixture of compounds containing Mb, Prepare a raw material solution containing each element of R, Ma, and Mb. And (2) a liquid phase synthesis step for obtaining a precursor solid of a dielectric compound from a raw material solution by a liquid phase method, and (3) a precursor solid obtained in the liquid phase synthesis step at a predetermined firing temperature. And a firing step of obtaining a dielectric compound powder by heating.

Thus, in the method using the liquid phase method, the reaction rate is faster than in the case of using the solid phase method, and it is possible to synthesize the compound by heating in a short time. In addition, even when the firing temperature is low, the compound can be suitably synthesized, and the resulting dielectric compound powder can be sufficiently finely divided. As described above, according to the above method, the dielectric compound (RMbO _3-δ ) _n (MaO) _m having a layered triangular lattice structure can be synthesized efficiently and under suitable conditions.

Here, regarding a specific method for synthesizing the dielectric compound, in the firing step, the precursor solid is preferably heated in a furnace at 700 ° C. or higher with an oxygen partial pressure of 10 ⁻¹² to 1 Pa for 1 minute or longer. From the state heated to 700 ° C. or higher in the firing step, it is preferable to cool to 200 ° C. or lower within 30 minutes. Ma and Mb are Fe, and the ratio of Fe ²⁺ to Fe ³⁺ in the raw material solution is preferably 0.5 to 1.5. The particle size of the powder obtained by firing the precursor solid is preferably 1 to 100 nm.

Further, in the dielectric compound of the present invention, the composition is (RMbO3 _-δ ) _n (MaO) _m (R is In, Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, Ti, Ca, Sr. , Ce, Sn, Hf, at least one element selected from the group consisting of Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, and Cd is allowed at least one type Element, n is an integer of 1 or more, m is an integer of 0 or more, and δ is a real number of 0 or more and 0.2 or less, and has a layered triangular lattice structure, a dielectric compound (RMbO _{3 _-δ)} _n (MaO) compounds containing R as a raw material for _m, using a compound containing Ma, and R generated by mixing a compound containing a Mb, Ma, a raw material solution containing each element Mb, liquid A dielectric compound precursor solid is generated by a phase method, The precursor solids are a powder obtained by heating to a predetermined firing temperature.

In particular, the particle size of the powder is preferably 1 to 100 nm.

Further, the precursor solid is preferably heated to a powder in an oven at 700 ° C. or higher with an oxygen partial pressure of 10 ⁻¹² to 1 Pa for 1 minute or more, and the powder is heated from 700 ° C. to 200 ° C. within 30 minutes. It is preferable to cool to below ℃.

Further, it is preferable that Ma and Mb are Fe and the ratio of Fe ²⁺ to Fe ³⁺ in the raw material solution is 0.5 to 1.5.

The dielectric compound produced by the production method of the present invention and the dielectric compound produced by this production method are obtained by synthesizing R, Ma, and R in the synthesis of the dielectric compound whose composition is represented by (RMbO _3-δ ) _n (MaO) _m . A layered triangular lattice is prepared by preparing a raw material solution containing each element of Mb, generating a precursor solid of a dielectric compound by a liquid phase method, and heating it at a predetermined firing temperature to obtain a powder of the dielectric compound. A dielectric compound such as RFe ₂ O ₄ having a structure can be efficiently synthesized.

FIG. 1 is a flowchart showing an embodiment of a method for producing a dielectric compound. FIG. 2 is a graph showing an X-ray diffraction pattern of a dielectric compound powder obtained using a liquid phase method and a solid phase method. FIG. 3 shows SEM images of dielectric compound powders obtained using the liquid phase method and the solid phase method. FIG. 4 is a graph showing an X-ray diffraction pattern of a dielectric compound powder obtained using a method in which a raw material solution is dropped into a base solution by a coprecipitation method. FIG. 5 is a graph showing an X-ray diffraction pattern of a dielectric compound powder obtained using a method in which a base solution is dropped into a raw material solution by a coprecipitation method. FIG. 6 is a graph showing an X-ray diffraction pattern of a dielectric compound powder obtained by cooling under different cooling conditions after firing. FIG. 7 is a graph showing the magnetic characteristics of the dielectric compound powder. FIG. 8 is a graph showing a Mossbauer spectrum of a dielectric compound powder. FIG. 9 is a graph showing an X-ray diffraction pattern of a dielectric compound powder. FIG. 10 is a graph showing an X-ray diffraction pattern of a dielectric compound powder.

Hereinafter, preferred embodiments of a method for producing a dielectric compound according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.

FIG. 1 is a flowchart showing an embodiment of a method for producing a dielectric compound. In the manufacturing method of the present embodiment, the compound to be synthesized is a dielectric compound RFe ₂ O _4-δ having a layered triangular lattice structure. Here, R represents at least one element selected from In, Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, Ti, Ca, Sr, Ce, Sn, and Hf, and oxygen deficiency. δ is a real number between 0 and 0.2.

As described above, such a dielectric compound RFe ₂ O _4-δ has recently been attracting attention as a substance that exhibits dielectric properties based on a principle different from that of conventional ferroelectrics. In the following, the description of oxygen deficiency δ is omitted except where particularly necessary, and is simply expressed as RFe ₂ O ₄ .

First, the outline of the dielectric compound manufacturing method according to the present embodiment will be described.

In the manufacturing method shown in FIG. 1, first, a compound containing R and a compound containing Fe are prepared as raw materials for the dielectric compound RFe ₂ O ₄ . And those compounds are mixed and the raw material solution containing each element of R and Fe is prepared (step S101, preparation process).

Next, a raw material solution containing R and Fe and a separately prepared base solution are mixed, and a precursor (hydroxide) that is a precursor solid of RFe ₂ O ₄ is obtained by a kind of coprecipitation method of a liquid phase method. A precipitate is generated (S102, coprecipitation step, liquid phase synthesis step).

Further, if necessary, the obtained precipitate of RFe ₂ O ₄ precursor is subjected to treatment such as washing and filtration (S103, washing step).

Subsequently, the precursor precipitate obtained by the coprecipitation method is subjected to heat treatment at a predetermined baking temperature for a predetermined baking time. Thereby, a powder of the dielectric compound RFe ₂ O ₄ is generated (S104, firing step).

In addition, the generated RFe ₂ O ₄ powder is subjected to an evaluation process such as characteristic measurement (S105, evaluation step). In addition, about this evaluation process, it is good also as a structure which is not performed if unnecessary.

The effect of the manufacturing method of the dielectric compound RFe ₂ O _4-δ according to the above embodiment will be described.

In the production method shown in FIG. 1, in the synthesis of the dielectric compound RFe ₂ O ₄ , instead of the conventionally used solid phase reaction method, a raw material solution containing each element of R and Fe is prepared and the liquid phase method is used. A precursor precipitate (precursor solid) is produced by a coprecipitation method which is a kind of the above. Then, the method for obtaining a powder precipitate was calcined under predetermined conditions dielectric compound in the precursor, which was synthesized compound RFe ₂ O _4.

Thus, in the method using the coprecipitation method, the reaction rate is faster than in the case of using the solid phase method, and it is possible to synthesize the compound by heating in a short time. In addition, even when the firing temperature is low, the compound can be suitably synthesized, and the resulting compound RFe ₂ O ₄ powder can be sufficiently finely divided. As described above, according to the above-described manufacturing method, it is possible to synthesize a dielectric compound RFe ₂ O ₄ having a layered triangular lattice structure efficiently, and preferred conditions.

With respect to the dielectric compound to be synthesized in the above manufacturing method, RFe ₂ O _4-δ is targeted in the embodiment of FIG. Generally, such a manufacturing method has a crystal structure and characteristics similar to those of RFe ₂ O ₄ , a composition represented by (RMbO _3-δ ) _n (MaO) _m , and a dielectric having a layered triangular lattice structure It can be suitably applied to a compound.

Here, R is at least one element selected from In, Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, Ti, Ca, Sr, Ce, Sn, and Hf, and Ma and Mb are Ti. , Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, Cd, at least one element selected with duplication allowed, n is an integer of 1 or more, m is an integer of 0 or more, and δ is 0 or more of 0 A real number of 2 or less.

RFe ₂ O _4-δ exemplified in the above embodiment corresponds to a case where Ma = Mb = Fe and n = m = 1 in the composition formula (RMbO _3-δ ) _n (MaO) _m .

Further, when the compound (RMbO _3-δ ) _n (MaO) _{m is} to be synthesized, in the preparation step (step S101 in FIG. 1), the compound containing R, the compound containing Ma, and the Mb, which are raw materials for the compound, A compound solution, preferably a solution of these compounds is mixed to prepare a raw material solution containing each element of R, Ma, and Mb.

The subsequent coprecipitation step (liquid phase synthesis step), washing step, and firing step (S102 to S104) are the same as in the case of RFe ₂ O _4-δ .

Further, in the above-described embodiment, for the liquid phase synthesis step for generating the precursor of the dielectric compound, the raw material solution and the base solution are mixed, and the precipitate of the precursor that is the precursor solid of the dielectric compound is obtained by the coprecipitation method. Use coprecipitation process. As described above, the synthesis using the coprecipitation method, which is a kind of liquid phase method, enables the dielectric compound to be synthesized in a suitable and reliable manner.

Further, as for the liquid phase method, specifically, other methods besides the coprecipitation method may be used. In general, in the liquid phase synthesis step, a method of obtaining a precursor solid of a dielectric compound from a raw material solution by a liquid phase method can be used. Thus, by using the liquid phase method for the synthesis of the precursor solid of the dielectric compound, uniform mixing of the raw materials at the atomic level is realized, and the synthesis at a low firing temperature is facilitated. In addition, the resulting compound powder can be expected to have effects such as fine particle formation and improved characteristics.

A specific example of the method for producing the dielectric compound shown in FIG. 1 will be described. Here, the compound RFe ₂ O ₄ to be synthesized is LuFe ₂ O ₄ . First, as a preparation stage for the synthesis of a compound, a raw material solution containing Lu (= R) and Fe is prepared (S101).

Specifically, first, a first solution composed of a solution of a compound containing Lu is prepared. In this first solution, Lu ₂ O ₃ weighed to 0.5 g (1.25 mmol) is dissolved in 4 ml of hot concentrated nitric acid (HNO ₃ , 60 wt%) to form a Lu ³⁺ solution. Then, once the solvent is completely evaporated, 4 ml of concentrated nitric acid is added again at room temperature to completely dissolve it.

Next, the 2nd solution consisting of the solution of the compound containing Fe is produced. In the second solution, the Fe ²⁺ solution is most simply prepared by adding 10 ml of distilled water to FeC ₂ O ₄ .2H ₂ O weighed to 0.9 g (5 mmol). At this stage, iron oxalate is not completely dissolved.

Here, by using not only iron oxalate but also iron sulfate, a solution containing Fe ²⁺ and Fe ³⁺ can be obtained in a solution of a compound containing Fe. In particular, the ratio of Fe ²⁺ to Fe ³⁺ in the solution can be adjusted to 0.5 to 1.5 by adjusting the blending ratio of iron oxalate and iron sulfate.

Subsequently, a mixed solution of the first solution and the second solution to be a raw material solution is prepared. This mixed solution is prepared by adding the second solution to the first solution obtained in the above step. At this time, in the second solution, the contents of the beaker are washed out with a small amount of distilled water so that iron oxalate or iron sulfate remaining at the bottom of the beaker is completely moved to the first solution side.

Thereby, the iron oxalate or iron sulfate remaining undissolved in the second solution is completely dissolved after mixing with the first solution, and a transparent mixed solution is obtained. This mixed solution becomes a raw material solution for the LuFe ₂ O ₄ synthesis.

Next, LuFe ₂ O ₄ precursor (hydroxide) powder is synthesized by coprecipitation reaction (S102, S103).

In the coprecipitation reaction, in this embodiment, the mixed raw material solution obtained in the above step is dropped dropwise with a dropper into 10 ml of NH ₃ water (28 wt%) as a base solution with stirring. And a base solution are mixed. In the case where precipitation of the metal components with the mixing of the raw material solution and the base solution does not occur, it may be used aqueous NaOH in place of NH ₃ water.

By mixing the raw material solution and the base solution to cause a coprecipitation reaction, a precursor solid of the dielectric compound LuFe ₂ O ₄ is generated as a precipitate at the bottom of the beaker.

Subsequently, the generated precipitate is filtered through a membrane filter (0.2 μm), and the precipitate is rinsed once with distilled water. The obtained precipitate is dried in a dryer at 100 ° C. for 24 hours.

The dried precursor solid is in the form of a powder having a particle size of 1 to 100 nm, and if this precursor solid is baked as it is, a dielectric compound having a particle size of 1 to 100 nm can be obtained. it can.

Subsequently, the LuFe ₂ O ₄ phase is synthesized by firing (S104). In the following, the case of firing as a pellet for measuring physical property values will be described.

First, dry powder of the precursor precipitate produced in the above process is put into a φ12 mm mold and press-molded into a pellet.

Then, the obtained pellet-shaped sample is vacuum fired. Specifically, a sample is put into a quartz tube sealed on one side, and a vacuum is drawn from the other side with a rotary pump. This quartz tube is put into an electric furnace and heated from a room temperature to a predetermined firing temperature (for example, 900 ° C.) at a predetermined temperature increase rate (for example, 10 ° C./min). At this time, the inside of the quartz tube is continuously evacuated by a rotary pump.

When the electric furnace reaches a predetermined temperature, the electric furnace is held at that temperature for a predetermined baking time (for example, 1 hour). Similarly, during this time, the inside of the quartz tube is continuously evacuated by the rotary pump.

When the firing time has elapsed, the quartz tube is quickly taken out of the electric furnace, immediately put into water and rapidly cooled. At this time, the inside of the quartz tube is continuously evacuated by the rotary pump. Thus, a powder of the dielectric compound LuFe ₂ O ₄ is obtained.

In the above manufacturing process, a method of strictly controlling the O ₂ partial pressure of the reaction field by flowing a CO / CO ₂ mixed gas into the quartz tube may be used for a portion that is evacuated by a rotary pump.

Also, the powder of a compound LuFe ₂ O ₄ obtained by the above method may be carried out Characterization if necessary (S105). As a method for evaluating the compound powder in this case, specifically, for example, identification of a generated phase by X-ray diffraction, particle shape and size evaluation by a scanning electron microscope (SEM), and sample vibration magnetometer (VSM) Examples include evaluation of magnetism and evaluation of electronic state by Mossbauer spectroscopy.

As described above, the RFe ₂ O ₄ powder synthesis method using the liquid phase method such as the coprecipitation method can suitably synthesize the compound at a low temperature in a shorter time than the solid phase method. In addition, the compound powder can be sufficiently finely divided.

That is, in the synthesis by the solid phase method, since the reaction rate is slow, heating and baking for several hours or more, usually 12 hours or more are required at least. In contrast, in the synthesis by the liquid phase method, since the reaction rate is fast, the synthesis can be performed in a short time.

FIG. 2 is a graph showing an X-ray diffraction pattern of a dielectric compound powder obtained by using a liquid phase method and a solid phase method. FIG. 2 (a) shows a case where baking is performed at 900 ° C. for 1 hour. FIG. 2B shows the X-ray diffraction result of the compound powder obtained by firing for 1 hour at a firing temperature of 1200 ° C. Here, Rigaku RINT2000 is used as an X-ray diffractometer, and measurement is performed by a powder X-ray diffraction method using Cu—Kα rays (output: 40 kV, 200 mA).

2A and 2B, graphs A1 and A3 show the results of compound synthesis by the liquid phase method, and graphs A2 and A4 show the results of synthesis by the conventional solid phase method. As shown in these graphs, in both 900 ° C. firing and 1200 ° C. firing, the liquid phase method obtained the LuFe ₂ O ₄ phase in a substantially single phase in a short time firing as compared with the solid phase method. You can see that

Further, the crystallite size of the LuFe ₂ O ₄ powder was determined from these X-ray diffraction results. Under the firing conditions of 900 ° C. for 1 hour, the liquid phase method was 49.7 nm, the solid phase method was 63.3 nm, and 1200 Under baking conditions of 1 ° C. for 1 hour, the liquid phase method was 73.5 nm and the solid phase method was 72.9 nm.

FIG. 3 is a view showing an SEM image of a dielectric compound powder obtained by using the liquid phase method and the solid phase method, and FIG. FIG. 3 (b) shows an SEM photograph of the compound powder obtained by firing the synthesized powder by the solid phase method at a firing temperature of 900 ° C. for 1 hour. Is shown.

As shown in these results, for the finally obtained compound powder, almost the same results were obtained in the solid phase method and the liquid phase method at a firing temperature of 1200 ° C., but the low temperature synthesis at a firing temperature of 900 ° C. Then, it can be seen that LuFe ₂ O ₄ obtained by the liquid phase method is finer than the solid phase method.

Next, a specific synthesis method and synthesis conditions in the synthesis of the dielectric compound RFe ₂ O ₄ powder by the coprecipitation method shown in FIG. 1 will be described together with corresponding measurement data.

FIG. 4 is a graph showing an example of an X-ray diffraction pattern of a dielectric compound powder obtained using a coprecipitation method. Here, as a method for generating a precipitate of the precursor of the compound LuFe ₂ O ₄ by a coprecipitation method, a method of generating a precipitate by dropping a mixed solution that is a raw material solution into NH ₃ water that is a base solution, The X-ray-diffraction result of the compound powder synthesize | combined by heating the obtained deposit at the predetermined baking temperature for 1 hour in a vacuum is shown.

In FIG. 4, graphs B1, B2, and B3 show the synthesis results when the firing temperatures are 900 ° C., 800 ° C., and 700 ° C., respectively. As shown in these graphs, in the synthesis of the compound using the coprecipitation method, a LuFe ₂ O ₄ phase is generated to some extent even at a firing temperature of 700 ° C., and further, at a firing temperature of 800 ° C. and 900 ° C., LuFe ₂ it can be seen that the O ₄ phase are mass produced.

FIG. 5 is a graph showing another example of an X-ray diffraction pattern of a dielectric compound powder obtained by using a coprecipitation method. Here, as a method of generating a precipitate of the precursor of the compound LuFe ₂ O ₄ by the coprecipitation method, unlike the above method, a method of generating a precipitate by dropping NH ₃ water into the mixed solution is used. The X-ray-diffraction result of the compound powder synthesize | combined by heating the obtained deposit at the predetermined baking temperature for 1 hour in a vacuum is shown.

In FIG. 5, graphs C1, C2, and C3 show the synthesis results when the firing temperatures are 900 ° C., 800 ° C., and 700 ° C., respectively. As shown in these graphs, in the method in which the base solution is dropped into the raw material solution in the coprecipitation method, the LuFe ₂ O ₄ phase is generated, but the method of dropping the raw material solution into the base solution is used. As compared with the above, even when the firing temperature is 900 ° C., a large amount of different phases such as Lu ₂ O ₃ and FeO are mixed, and it is difficult to make LuFe ₂ O _{4 into} a single phase under the firing conditions for 1 hour. .

As described above, when the coprecipitation method is used for the generation of the precursor of the dielectric compound, the specific synthesis conditions and synthesis method are dropped while stirring the raw material solution in the base solution in the coprecipitation step. It is preferable to mix the raw material solution and the base solution.

Here, in a normal coprecipitation method, a base solution is dropped onto the raw material solution side, and the pH is raised to a predetermined value to obtain a precursor (hydroxide) precipitate (see FIG. 5). In this case, since the solubility of ions generally varies depending on the ion species, for example, in the synthesis of RFe ₂ O ₄ , the composition of R ³⁺ , Fe ²⁺ , and Fe ³⁺ changes between the initial and final stages of precipitation by coprecipitation reaction There is a possibility that.

On the other hand, by dropping the raw material solution into the base solution while vigorously stirring (see FIG. 4), it becomes possible to generate a precursor precipitate with a uniform composition from the beginning to the end of the precipitation.

Further, as the base solution used in the coprecipitation step, it is preferable to use an ammonia solution (NH ₃ solution). In addition to the NH ₃ solution, various base solutions such as a NaOH solution can be used. However, when an NaOH solution is used, Na may enter impurities in the resulting dielectric compound powder, which may affect the physical properties thereof. Therefore, the NH ₃ solution is more preferable in this respect.

As for the specific starting material compounds used in the raw material solution, in the above example, for compounds LuFe ₂ O ₄ to be combined, _Lu 2 _{O 3,} nitric _acid, are used FeC _₂ O 4 · 2H ₂ O However, not limited to the above, various raw materials may be used. For example, as a compound containing Lu (compound containing R), the above-described Lu ₂ O ₃ is available at a low price, but other compounds may be used as raw materials. In addition, for iron-containing compounds, other iron compounds such as iron chloride and iron sulfate may be used. In the above example, iron oxalate is used in consideration of the influence of the residual elements after synthesis.

In addition to the nitric acid described above, other acids such as sulfuric acid and hydrochloric acid may be used as the acid for dissolving Lu ₂ O ₃ in water. However, in the case of sulfuric acid, hydrochloric acid, etc., it is considered that trace amounts of elements such as S and Cl may remain as impurities in the final product, LuFe ₂ O ₄ crystal. Yes.

In addition, regarding the firing conditions of the precursor obtained by a liquid phase method such as a coprecipitation method, it is preferable to heat the precursor solid at a firing temperature of 900 ° C. or less in the firing step. In this case, the synthesis of the dielectric compound can be performed at a sufficiently low temperature.

4 and 5 show the synthesis results of the compounds at a firing temperature of 700 ° C. to 900 ° C. By firing at 700 ° C. or higher, the precursor can be reliably sintered. Further, as shown in FIG. 2, the synthesis is possible even at a firing temperature higher than 900.degree.

Furthermore, regarding the firing time, it is preferable that the precursor solid is heated for a firing time of 2 hours or less in the firing step. In this case, the synthesis of the dielectric compound can be performed in a sufficiently short time.

In particular, when firing in an atmosphere in which the oxygen partial pressure is adjusted to 10 ⁻¹² to 1 Pa, the precursor solid can be sintered only by maintaining the state of 700 ° C. or higher for 1 minute or longer. The processing time can be greatly reduced and the manufacturing cost can be greatly reduced.

In order to perform such firing, the precursor solid can be effectively fired by using a rotary kiln furnace. In particular, when a rotary kiln furnace is used, a dielectric compound can be obtained directly from a precursor solid in a powder state, and the manufacturing cost can be easily reduced.

Moreover, it is preferable to suppress the appearance of grain growth and different crystalline states by rapidly cooling the sintered dielectric compound. From the state heated to 700 ° C. or higher to 200 ° C. or lower within 30 minutes. It is preferable to cool.

In the simplest case, the dielectric compound heated to 700 ° C. or higher and sintered can be simply taken out of the heating furnace, and the dielectric compound can be discharged out of the heating furnace with an appropriate discharging means to be naturally cooled. You can just let it.

FIG. 6 is a graph showing an X-ray diffraction pattern of a powder of the dielectric compound LuFe ₂ O ₄ when the dielectric compound heated to 800 ° C. and sintered is cooled under different cooling conditions. F1 in FIG. 6 is a graph when the precursor solid is heated at 800 ° C. for 1 hour and calcined and then rapidly cooled by taking it out of the heating furnace. F2 in FIG. After heating for 1 hour and baking, the heating condition of the heating furnace is controlled and the temperature is cooled to 200 ° C. or less over about 3 hours.

As shown in the graph, it can be seen that the LuFe ₂ O ₄ phase can be effectively generated by rapid cooling.

FIG. 7 is a graph showing the magnetic properties (magnetization-temperature curve) of the LuFe ₂ O ₄ powder synthesized by the above method using the coprecipitation method.

FIG. 8 is a graph showing the room temperature Mossbauer spectrum of the LuFe ₂ O ₄ powder. Here is shown the measurement results of the NH ₃ compound powder mixed solution precipitate obtained was added dropwise to have been fired to synthesize at 900 ° C. in water is a base solution.

As shown in these graphs, the LuFe ₂ O ₄ crystal powder obtained by the above method has the same characteristics as the LuFe ₂ O ₄ crystal synthesized using the solid phase method (Non-patent Document). 6). That is, it is considered that the RFe ₂ O ₄ crystal synthesized using the coprecipitation method exhibits the same interesting physical properties as those of the RFe ₂ O ₄ crystal synthesized using the solid phase method so far. .

Next, the firing time in firing the precursor solid of the dielectric compound obtained by the coprecipitation method will be described.

FIG. 9 is a graph showing an X-ray diffraction pattern of a powder of dielectric compound LuFe ₂ O ₄ obtained by the above synthesis method. Here is shown the measurement results of the NH ₃ compound powder mixed solution precipitate obtained was added dropwise to have been fired to synthesize at 900 ° C. in water is a base solution.

In FIG. 9, graphs D1, D2, D3, and D4 show the synthesis results when the firing time is 2 hours, 1 hour, 0.5 hours, and 0 hours, respectively. The firing time of 0 hour means that the quartz tube containing the sample is heated from room temperature to a firing temperature of 900 ° C. at a predetermined rate of temperature rise, and when the temperature reaches 900 ° C., the sample is not held at the firing temperature. The case where the heat treatment is immediately finished is shown.

As shown in these graphs, even when the firing time (holding time at a firing temperature of 900 ° C.) is 0 hour, the LuFe ₂ O ₄ phase is considerably generated. From this, it can be seen that according to the synthesis method described above, the compound powder can be synthesized even in a very short time. However, in the synthesis example shown in FIG. 9, the Lu ₂ O ₃ phase exists to some extent when firing is performed for a short time. On the other hand, when firing for a relatively long time at 1 hour or longer, the Lu ₂ Fe ₃ O ₇ phase appears.

Next, the concentration of the raw material solution in the coprecipitation method, specifically, the concentration of the mixed solution dropped into the NH ₃ water that is the base solution will be described.

FIG. 10 is a graph showing an X-ray diffraction pattern of a powder of dielectric compound LuFe ₂ O ₄ obtained by the above synthesis method. Here, Lu 3+ to NH ₃ in ^water, the precipitate obtained was added dropwise to Fe ²⁺ solution 900 ° C., shows the measurement results for compound powder fired to synthesized in 1 hour.

Further, in FIG. 10, graphs E1, E2, and E3 show the synthesis results when the concentration of the LuFe ₂ aqueous solution is 0.05 mol / l, 0.1 mol / l, and 0.2 mol / l, respectively.

In these graphs, the LuFe ₂ O ₄ phase is generated in the entire concentration range. In addition, when the synthesis results at each concentration are compared, the LuFe ₂ aqueous solution concentration is 0.1 mol / l, which is closest to the single phase of the LuFe ₂ O ₄ phase, and in other cases, the LuFeO ₃ phase, which is a different phase, is present. It is mixed.

The results shown in FIGS. 9 and 10 for the firing time and the concentration of the raw material solution can be further improved by controlling other synthesis conditions such as oxygen partial pressure during firing. It seems possible.

The method for producing a dielectric compound according to the present invention is not limited to the above-described embodiment and configuration examples, and various modifications are possible.

For example, the conditions for generating the precursor solid of the dielectric compound by the coprecipitation method and the firing conditions of the precursor solid are not limited to the above-described conditions, and various conditions may be changed as necessary.

Also, as described above, various methods other than the coprecipitation method may be used as the liquid phase method used for producing the precursor solid of the dielectric compound. Examples of such a liquid phase method include a sol-gel method using a metal alkoxide as a raw material and a complex polymerization method using an organometallic complex as a raw material.

The present invention can be used as a method for producing a dielectric compound capable of suitably synthesizing a dielectric compound such as RFe ₂ O ₄ .

S101 Preparatory process S102 Coprecipitation process (liquid phase synthesis process)
S103 Cleaning step S104 Firing step S105 Evaluation step

Claims

The composition is at least selected from (RMbO3 -δ ) n (MaO) m (R is selected from In, Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, Ti, Ca, Sr, Ce, Sn, Hf. One element, Ma and Mb, is at least one element selected from Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, and Cd, allowing overlap, n is an integer of 1 or more, m Is an integer greater than or equal to 0 and δ is a real number greater than or equal to 0 and less than or equal to 0.2, and is a method for producing a dielectric compound having a layered triangular lattice structure,
Dielectric compound (RMbO 3-δ ) n (MaO) A raw material solution containing R, Ma, and Mb elements by mixing a compound containing R, a compound containing Ma, and a compound containing Mb as raw materials for m A preparation process to prepare,
A liquid phase synthesis step of obtaining a precursor solid of the dielectric compound from the raw material solution by a liquid phase method;
A method for producing a dielectric compound, comprising: a step of heating the precursor solid obtained in the liquid phase synthesis step at a predetermined firing temperature to obtain a powder of the dielectric compound.
The method for producing a dielectric compound according to claim 1, wherein the particle size of the dielectric compound in the powder obtained in the firing step is 1 to 100 nm.
3. The firing process according to claim 1, wherein, in the firing step, the precursor solid is heated in a furnace at 700 ° C. or higher with an oxygen partial pressure of 10 −12 to 1 Pa for 1 minute or longer. A method for producing a dielectric compound.
The method for producing a dielectric compound according to claim 3, wherein the dielectric compound is cooled to 200 ° C. or less within 30 minutes after being heated to 700 ° C. or more in the firing step.
5. The Ma and the Mb are Fe, and an abundance ratio of Fe 2+ to Fe 3+ in the raw material solution is set to 0.5 to 1.5. A method for producing the dielectric compound as described.
The composition is at least selected from (RMbO3 -δ ) n (MaO) m (R is selected from In, Sc, Y, Dy, Ho, Er, Tm, Yb, Lu, Ti, Ca, Sr, Ce, Sn, Hf. One element, Ma and Mb, is at least one element selected from Ti, Mn, Fe, Co, Cu, Ga, Zn, Al, Mg, and Cd, allowing overlap, n is an integer of 1 or more, m Is an integer greater than or equal to 0, δ is a real number greater than or equal to 0 and less than or equal to 0.2, and is a dielectric compound having a layered triangular lattice structure,
Dielectric Compound (RMbO 3-δ ) n (MaO) Raw material containing R, Ma, and Mb elements formed by mixing R-containing compound, Ma-containing compound, and Mb-containing compound as raw materials for m A dielectric compound characterized by being a powder obtained by producing a precursor solid of the dielectric compound by a liquid phase method using a solution and heating the precursor solid to a predetermined firing temperature.
The dielectric compound according to claim 6, wherein the powder has a particle size of 1 to 100 nm.
8. The dielectric according to claim 6, wherein the precursor solid is heated in a furnace at 700 ° C. or higher with an oxygen partial pressure of 10 −12 to 1 Pa for 1 minute or longer to obtain the powder. Body compounds.
The dielectric compound according to claim 8, wherein the powder is cooled from 700 ° C. to 200 ° C. within 30 minutes.
10. The Ma and the Mb are Fe, and the existence ratio of Fe 2+ to Fe 3+ in the raw material solution is set to 0.5 to 1.5. The dielectric compound described.