JP6877994B2 - Apatite type composite oxide and its manufacturing method, solid electrolyte type device and sputtering target - Google Patents

Description

The present invention provides solid electrolytes for batteries such as solid electrolyte fuel cells (SOFCs), ion batteries, and air batteries, separation membranes such as oxygen concentrators and oxygen separation membranes, and apatites that can be used for oxygen sensors, sputtering targets, and the like. The present invention relates to a type composite oxide and a method for producing the same.

As functional ceramics, composite oxides that utilize electrical conduction by oxygen ions are being studied. For example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 8-208333), a composite oxide having a hexagonal crystal system as a main constituent phase mainly composed of a rare earth element such as Ce and a silicon oxide has high ionic conductivity. It has been reported that it can be applied to oxygen sensors, solid-state batteries, etc. because the rate can be obtained.

Further, in Patent Document 2 (Japanese Patent Laid-Open No. 11-71169) and Patent Document 3 (Japanese Patent Laid-Open No. 11-130595), (RE ₂ O ₃ ) _x (SiO ₂ ) ₆ (RE is La, Ce, Pr. , Nd, Sm, x is a sintered body containing 3.5 <x <6 as a main component), and the main constituent phase of the sintered body is an apatent crystal structure. It has been reported that oxides can obtain high conductivity even in a low temperature range.

Further, in Patent Document 4 (International Publication No. 2016/11110), A _9.33x [ _{T6- y My} ] O26.00 + z (A is La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, It is an element selected from Dy, Be, Mg, Ca, Sr, and Ba, T is Si or Ge, M is an element selected from B, Ge, Zn, Sn, W, and Mo, and x. Is -1 to 1, y is 1 to 3, z is -2 to 2, and the number of moles of A is 3 to 10 with respect to the number of moles of M). Things have been proposed.

Japanese Unexamined Patent Publication No. 8-208333 Japanese Unexamined Patent Publication No. 11-71169 Japanese Unexamined Patent Publication No. 11-130595 International Publication 2016/1111010

The apatite-type composite oxide containing a rare earth element such as Ce and a silicon oxide as a main component as described above loses conductivity in a high temperature range exceeding 400 ° C., and its use may be limited. It was.

In response to the above problems, the present inventors have changed the apatite structure of an apatite-type composite oxide containing a rare earth element such as Ce and a silicon oxide to a composite oxide containing a fluorite structure in a high temperature region. , I noticed that the conductivity decreases due to the association phenomenon between oxygen vacancies and guest cations. As a result of further diligent studies, the present inventors have obtained a sintered body containing at least one of Group 2 elements Mg, Ca, Sr, and Ba in a specific ratio in the cerium silicate composite oxide. As a result, it was found that the apatite structure can be maintained even in a high temperature region, and as a result, a composite oxide capable of achieving high conductivity even in a high temperature region can be obtained. The present invention is based on such findings.

Therefore, an object of the present invention is to provide a composite oxide capable of maintaining an apatite structure even in a high temperature region and, as a result, realizing high conductivity even in a high temperature region. Another object of the present invention is to provide a method for producing the composite oxide. Yet another object of the present invention is to provide a solid electrolyte type device and a sputtering target using the composite oxide.

Apatite type composite oxide according to the present invention, the composition _{formula: Ce x M y Si 6 O} z
(During the ceremony,
M is at least one element selected from the group consisting of Mg, Ca, Sr and Ba.
x is in the range of 6.0 ≤ x ≤ 9.6.
y is in the range of 0.4 ≦ y ≦ 4.0,
However, 8.0 ≦ (x + y) ≦ 10.0 is satisfied, and
z is in the range of (1.5x + y + 12) ≦ z ≦ (2x + y + 12). )
It is represented by.

Further, the method for producing an apatite-type composite oxide according to another aspect of the present invention is described.
A step of forming a mixture such that the element ratio is Ce: M: Si = x: y: 6 (where M, x, and y are the same as the above definitions).
The mixture was sintered in an inert gas atmosphere, the composition _{formula: Ce x M y Si 6 O} z ( where, x, y and z are as defined above.) Step of a sintered body having a When,
A step of heat-treating the sintered body in an oxygen-presence atmosphere so that the ratio of Ce (tetravalence) in the Ce element is 20 atm% or more.
Are prepared in this order.

Further, the solid electrolyte type element according to another aspect of the present invention is a solid electrolyte type element including a solid electrolyte and at least one electrode provided on the surface of the solid electrolyte, and the solid electrolyte is a solid electrolyte type element. It is composed of the above-mentioned apatite-type composite oxide.

In the embodiment of the present invention, the solid electrolyte has a multi-layer structure, at least one layer of the multi-layer structure is made of the apatite-type composite oxide, and an electrode is provided on the surface of the layer made of the apatite-type composite oxide. It may have been.

Further, the present invention also provides a sputtering target made of the above-mentioned apatite-type composite oxide.

In the present invention, the cerium silicate composite oxide has an apatite structure even in a high temperature region by forming a sintered body containing at least one of Group 2 elements Mg, Ca, Sr, and Ba in a specific ratio. As a result, a composite oxide having high conductivity even in a high temperature region can be realized.

The X-ray diffraction pattern of the composite oxide after the heat treatment obtained in Example 3. Evaluation result of electromotive force of oxygen concentration cell produced in Example 5.

<Apatite type composite oxide>
Apatite type composite oxide according to the present invention, the composition _{formula: Ce x M y Si 6 O z} ( wherein, M is at least one element selected from the group consisting of Mg, Ca, Sr and Ba, x Is in the range of 6.0 ≦ x ≦ 9.6, and y is in the range of 0.4 ≦ y ≦ 4.0, except that 8.0 ≦ (x + y) ≦ 10.0 is satisfied. , Z is in the range of (1.5x + y + 12) ≦ z ≦ (2x + y + 12)). As described above, cerium silicate, i.e. _{formula: Ce m (SiO 4) 6} O n ( where, m and n is a real number) apatite-type composite oxide represented by, in 400 ° C. or higher high-temperature range, apatite The structure changes to a structure including apatite structure, and the conductivity decreases. On the other hand, it was unexpected that the apatite structure was maintained even in a high temperature region by using a cerium silicate containing a Group 2 element as in the present invention in a predetermined ratio.

In the present invention, whether or not the composite oxide has an apatite structure can be confirmed by X-ray diffraction (XRD). For example, in the case of a composite oxide in which M is Ce or Sr, the composite oxidation is carried out by confirming whether or not the composite oxide has a predetermined diffraction peak in the diffraction angle 2θ (deg) range of 10 ° to 80 ° on the XRD chart. It is possible to confirm whether or not the object has an apatite structure. For example, M can perform XRD analysis using powder of a composite oxide is Sr, by comparing the obtained diffraction pattern ICSD card, the composite oxide, space group belonged to P6 ₃ / m It can be confirmed that it has an apatite crystal structure.

Further, the apatite-type composite oxide according to the present invention may have a main phase having an apatite structure, and includes polycrystals other than a single crystal having an apatite structure. The ratio of the main phase having an apatite structure to the apatite-type composite oxide is preferably 50 mol% or more of the total crystal phase detected by X-ray diffraction. The ratio of the main phase can be calculated by analyzing the X-ray diffraction (XRD) pattern.

In the above composition formula, M represents at least one element selected from the group consisting of Mg, Ca, Sr and Ba, and Ca is preferable among these from the viewpoint of conductivity.

In the above composition formula, x is in the range of 6.0 ≦ x ≦ 9.6, but the lower limit of x is preferably 6.1, more preferably 6.2, and particularly preferably 6.3. Is. The upper limit of x is preferably 9.6, more preferably 9.0, and particularly preferably 8.6. On the other hand, when the lower limit of x is less than 6.0, although it has an apatite structure, the proportion of different phases increases and the conductivity decreases. Further, when x exceeds 9.6, the Ce element preferentially forms an apatite structure, which makes it difficult to introduce the M element.

Further, in the above composition formula, y is in the range of 0.4 ≦ y ≦ 4.0, but from the viewpoint of maintaining the apatite structure of the composite oxide even in a high temperature environment, the preferable lower limit value of y is 0. It is 5, more preferably 0.5, and particularly preferably 0.8. The upper limit of y is preferably 4.0, more preferably 3.8. In particular, from the viewpoint of maintaining the apatite structure of the composite oxide even in a high temperature environment, the range of y is preferably 0.8 ≦ y ≦ 3.8. On the other hand, when the lower limit of y is less than 0.4, the composite oxide having an apatite structure is a composite composed of CeO ₂ , SiO ₂ and MO in which the main phase has a fluorite structure in a high temperature region. It becomes an oxide and the conductivity decreases. Further, when the upper limit value of y exceeds 4.0, _{the proportion of the different phase M 2} SiO ₅ phase increases and the conductivity decreases.

In the above composition formula, x and y are in the above ranges, respectively, but in order for the composite oxide to have an apatite structure, x + y must be 8.0 or more and 10.0 or less. That is, in the crystal structure, the Ce and M elements are located at 8 to 10 sites with respect _{to the 6 SiO 4} tetrahedral sites, so that the space group becomes an apatite crystal structure belonging to _{P6 3 / m.}

Further, in the above composition formula, z is in the range of (1.5x + y + 12) ≦ z ≦ (2x + y + 12). When z (that is, the ratio of O element) is in the above range, the apatite structure can be significantly maintained.

In the apatite-type composite oxide represented by the above composition formula, the Ce element exists in the state of Ce (trivalent) and Ce (tetravalent). In order to realize good conductivity, it is preferable that more Ce (tetravalence) is present in the unit cell than Ce (trivalence). The proportion of Ce (tetravalence) in all Ce elements in the composite oxide is more preferably 20 atm% or more, and particularly preferably 25 atm% or more. Since the amount of oxygen in the crystal structure increases as the ratio of Ce (tetravalence) increases, excellent conductivity can be realized. Whether the Ce element in the apatite type composite oxide exists in the state of Ce (trivalent) or Ce (tetravalent) is determined by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), or the like. It can be identified using known elemental analysis techniques. For example, by performing XPS analysis and determining the peak area ratio of the peak (886 eV) derived from Ce (trivalent) and the peak (917 eV) derived from C (tetravalent), Ce (trivalent) or Ce (trivalent) in all Ce elements or The abundance ratio of Ce (tetravalent) can be obtained.

Next, a method for producing an apatite-type composite oxide according to the present invention will be described.
<Powder molding / sintering method>
First, cerium oxide (IV), that is, CeO ₂ , oxides of group 2 elements (Mg, Ca, Sr, Ba) and / or carbonates thereof (that is, MO and / or MCO ₃ ), and silicon dioxide, That is, SiO ₂ is mixed so that the element ratio is Ce: M: Si = x: y: 6 (where x and y are in the above numerical range) to obtain a mixture. As these oxides, it is preferable to use a powder, and usually, a powder having a particle size of about 0.5 to 5 μm, preferably about 0.5 to 3.0 μm is used. The ratio of each oxide may be weighed and mixed so that the element ratio is Ce: M: Si = x: y: 6. The particle size means the cumulative average particle size (D50) obtained by the laser diffraction / scattering method.

The mixing method is not particularly limited as long as the powders of each oxide can be uniformly mixed, and known wet mixing or dry mixing can be adopted. As an example, a uniform mixture can be obtained by putting each of the weighed oxides into a mortar or the like and mixing the powders while crushing them. In addition to the mortar, a stirrer such as a ball mill may be used. By setting the particle size to 0.5 μm to 3.0 μm as described above, the sintered body density can be increased.

If necessary, the obtained mixture may be calcined in advance before being sintered. The calcining is usually performed at about 1000 to 1300 ° C. In addition, calcining is usually carried out in the atmosphere or in an oxygen-existing atmosphere. The calcining time may be appropriately set according to the calcining temperature and the calcining atmosphere. The calcined mixture may be a lump, but in that case, it may be pulverized by a known method if necessary.

Subsequently, the mixture (in the case of calcining, the calcined body) is pressure-formed and sintered. As the sintering, either a powder sintering method or a thin film sintering method may be adopted. For example, when the powder sintering method is adopted, sintering is performed under pressurized conditions or normal pressure conditions. Pressurization can be performed using a known molding machine, for example, a rubber press molding machine, an extrusion molding machine, a hot press molding machine, or the like. Further, it may be formed into a desired shape by pressurizing. For example, it can be pressure-molded into a disk shape or a columnar shape.

The sintering temperature can be appropriately set depending on the composition of the mixture and the like, but is generally about 700 to 1700 ° C., preferably 800 to 1600 ° C. for 1 to 20 hours. Further, the sintering is preferably performed in an atmosphere of an inert gas such as nitrogen or argon. That is, by performing sintering in an atmosphere having a low oxygen content (an atmosphere in which the oxygen concentration is 1.0% or less, more preferably 0.01% or less), the composite oxide is a sintered body. Cerium has more trivalent states than tetravalent states, making it easier to adopt an apatite structure. For example, the ratio of Ce (trivalent) in the composite oxide obtained by sintering a mixture of _{CeO 2} , MO and / or MCO ₃ and SiO _{2 in a nitrogen atmosphere is based on the total Ce element.} The ratio of Ce (tetravalent) is about 0 to 40 atm% with respect to the entire Ce element. The atmosphere other than the inert atmosphere may be any atmosphere having a low oxygen content, for example, a vacuum atmosphere or a reducing atmosphere.

The heating rate and the sintering time may be appropriately changed depending on the raw material composition and the sintering temperature. For example, after the temperature is raised at a heating rate of 50 to 200 ° C./hour and sintering is performed, the temperature is increased to 50 to 300 ° C./hour. It is typically cooled to room temperature at an hourly rate of cooling.

As described above, the sintered body thus obtained has a large proportion of Ce (trivalent) in the total cerium element in the sintered body. In the present invention, in order to further improve the conductivity, the sintered body is heat-treated in an oxygen-presence atmosphere. By heat treatment in an oxygen-presence atmosphere, a part of Ce (trivalent) in the sintered body becomes Ce (tetravalent), and interstitial oxygen easily moves, so that it is considered that the conductivity is improved. That is, in the present invention, a sintered body having a more complete apatite structure is obtained by making it in a Ce (trivalent) rich state at the time of sintering, and then by heat treatment, Ce (3) in the sintered body is obtained. By oxidizing a part of the valence) with Ce (tetravalent), a composite oxide having excellent conductivity while maintaining the apatite structure is obtained. In the present invention, it is preferable to use an apatite-type composite oxide in which the ratio of Ce (tetravalence) in the Ce element is 20 atm% or more. In the apatite-type composite oxide after the heat treatment as described above, the ratio of Ce (tetravalence) in the Ce element is typically 90 atm% or less.

The temperature of the heat treatment is preferably 500 to 900 ° C, more preferably 700 to 850 ° C. The heat treatment time is preferably 10 minutes to 3 hours, more preferably 20 minutes to 2 hours. As the oxygen presence atmosphere, an atmosphere having an oxygen concentration of 5% or more is preferable, and a typical atmosphere is an atmospheric pressure atmosphere (oxygen concentration is about 21%), but even if heat treatment is performed in an atmosphere having a higher oxygen concentration. Good. By adopting such heat treatment conditions, the ratio of Ce (tetravalence) in the Ce element in the composite oxide can be set to 20 atm% or more. If the heat treatment temperature is less than 500 ° C., it may be insufficient to oxidize a part of Ce (trivalent) to Ce (tetravalent), and it is difficult to set the ratio of Ce (tetravalent) to 20 atm% or more. Become. On the other hand, when the heat treatment temperature exceeds 900 ° C., the apatite crystal structure begins to disappear.

<Sputtering film sintering method>
The apatite-type composite oxide according to the present invention can also be produced by a method other than the above-mentioned powder molding / sintering method. As an example, a thin film mixture (precursor) having an element ratio of Ce: M: Si = x: y: 6 (where M, x, and y are the same as the above definitions) by the sputtering method. ) Will be described.

First, a sintered body formed by a powder molding / sintering method or a heat-treated body thereof is used as a sputtering target, and a substrate placed on a counter electrode is placed. Subsequently, a thin film mixture (precursor) is obtained by applying a high frequency voltage between both electrodes and sputtering in the vacuum chamber. This sputtering can be carried out using a known sputtering apparatus.

The substrate before sputtering may be preheated, if necessary. Further, immediately before the sputtering film formation, it is preferable to put the inside of the chamber in a high vacuum state of ^{1 × 10 -3} to 1 × 10 ^{-5 Pa.} Further, at the time of sputtering film formation, in order to improve the discharge efficiency, the inside of the chamber may be filled with an inert gas such as Ar, He, Ne, Kr, Xe, Rn, and the pressure may be adjusted to about 0.5 Pa to 30 Pa. preferable. Further, it is preferable to set the power density (power value / film formation area) at the time of sputtering film formation to 0.5 to 2.0 W / cm ^{2 from the viewpoint of efficiently forming a film while preventing abnormal precipitation and sparks.} , More preferably 0.6 to 1.8 W / cm ² .

Immediately after the sputtering step was performed, the thin film mixture (precursor) obtained as described above was composed of the mixture in the powder molding / sintering method, that is, CeO ₂ , MO, and SiO ₂ . since the same composition in mixture with chemical, thin mixture against (precursor), by performing the sintering and heat treatment, the composition formula described _{above: Ce x M y Si 6 O} z ( where, x, y And z are the same as the above definition.) It is possible to obtain an apatite type composite oxide represented by. The sintering conditions and heat treatment conditions are the same as those of the powder molding / sintering method described above.

The above two preferable methods have been exemplified as a method for producing an apatite-type composite oxide according to the present invention, but the method is not limited to these, and known methods such as a sol-gel method, a hydrothermal synthesis method, and a wet synthesis method are used. An apatite-type composite oxide can also be obtained by the above method.

<Use of apatite-type composite oxide>
As an example of the usage pattern of the apatite type composite oxide according to the present invention, a solid electrolyte type element including a solid electrolyte composed of the apatite type composite oxide and at least one electrode provided on the surface of the solid electrolyte can be mentioned. be able to. The shape of the solid electrolyte is not limited. For example, in addition to the flat film shape, there may be a shape such as a cylindrical shape. For example, when the shape of a solid electrolyte composed of an apatite-type composite oxide is cylindrical, electrodes are usually formed on the inner peripheral surface and the outer peripheral surface thereof.

The solid electrolyte may have a multilayer structure. In that case, at least one layer of the multilayer structure may be made of the apatite-type composite oxide, and an electrode may be provided on the surface of the layer made of the apatite-type composite oxide. Since the apatite-type composite oxide according to the present invention is also a material having a relatively low surface resistance, it has a laminated structure in which a solid electrolyte having a high surface resistance is sandwiched between layers of the apatite-type composite oxide, and the apatite-type composite oxide is formed. By forming an electrode on the surface of the layer made of the above, a solid electrolyte type element having higher conductivity can be obtained. That is, the layer made of apatite-type composite oxide functions as an intermediate layer provided between the other solid electrolyte and the electrode. Such a multilayer structure can be produced by forming a thin film layer of an apatite-type composite oxide on the surface of another solid electrolyte by a sputtering method or the like. The other solid electrolyte can be used without particular limitation, but it is preferable to use one having a coefficient of thermal expansion close to that of the apatite-type composite oxide according to the present invention. For example, the lanthanum silicate-based composite oxide described in Patent Document 4 is used. Etc. can be preferably used.

The solid electrolyte type element as described above can also be used as a cell of a fuel cell (SOFC). For example, when fuel gas is supplied to the anode electrode of the electrode junction, and an oxidizing agent (air, oxygen, etc.) is supplied to the cathode electrode and operated at 350 to 1000 ° C., the oxygen atom that received electrons at the cathode electrode is operated. Becomes O ^2- ion and reaches the anode electrode via the solid electrolyte, where it combines with hydrogen and emits electrons to generate electricity.

Further, the solid electrolyte type element as described above can also be used as an oxygen sensor. For example, when one side of the electrode joint is exposed to the reference gas and the other side is exposed to the measurement atmosphere, an electromotive force is generated according to the oxygen concentration in the measurement atmosphere. Therefore, for example, by using the reference gas as the atmosphere and the measurement atmosphere as the exhaust gas from the internal combustion engine, it can be used for controlling the air-fuel ratio of the exhaust gas.

Further, the solid electrolyte type device as described above can also be used as an oxygen separation membrane or an oxygen enrichment device. For example, when air is supplied to the cathode electrode and operated at 350 to 1000 ° C. as in the case of using it as a cell of a fuel cell (SOFC), the oxygen atom that receives an electron at the cathode ^{becomes an O 2-} ion and becomes a solid. It reaches the anode electrode via the electrolyte, where it emits electrons and ^{binds O 2-} ions to each other, allowing only oxygen molecules to permeate.

The solid electrolyte type device having the above-mentioned multi-layer structure can be produced by forming a thin film layer made of an apatite type composite oxide on the surface of another solid electrolyte by a sputtering method or the like. Further, the apatite-type composite oxide according to the present invention can also be used as a sputtering target used when forming a thin film as described above. The sputtering target can be formed by the above-mentioned powder molding / sintering method, but the powder molded product before sintering is subjected to hot hydrostatic press (HIP) or cold isotropic pressure (CIP). It is also possible to obtain it by sintering it after molding it into a desired shape. The resulting sputtering target can be subjected to a process for smoothing the surface, for example, a mechanical polishing process. As a result, the occurrence of abnormal discharge and splash is effectively suppressed, and a better thin film can be formed more stably.

Next, embodiments of the present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

<Example 1>
The _{powders of CeO 2} , CaO, and SiO ₂ are blended so that the element ratio of Ce: Ca: Si is 8.6: 1.0: 6, then crushed in a mortar and used in a Pt crucible. It was calcined at 1300 ° C. for 5 hours in an air atmosphere. Next, the obtained calcined product was pulverized with a planetary ball mill, and the pulverized product was molded in a nitrogen atmosphere (oxygen concentration of 0.01% or less) under a pressure of 25 MPa with a hot press machine in a nitrogen atmosphere (oxygen). By sintering at a concentration of 0.01% or less), a disk-shaped (diameter 20 mm, thickness 2.0 mm) sintered body was obtained. Sintering was carried out by holding 1500 ° C. for 3 hours at a heating rate of 200 ° C./hour and cooling at a temperature decreasing rate of 200 ° C./hour.

Subsequently, the surface of the sintered body obtained as described above was polished with a diamond grindstone and then heat-treated to obtain a composite oxide. The heat treatment was carried out at 700 ° C. for 3 hours under an atmospheric pressure atmosphere (oxygen concentration 20.9%).

<Examples 2 to 4 and Comparative Examples 1 to 3>
A _{composite oxide was prepared in the same manner as in Example 1 except that the blending ratio of CeO 2} , CaO, and SiO ₂ was changed as shown in Table 1, and the composition and crystal structure were adjusted in the same manner as in Example 1. It was identified and the element ratios of C (trivalent) and Ce (tetravalent) were confirmed. Further, in Example 4, SrO was used instead of CaO, and the compound oxide was the same as in Example 1 except that the blending ratio of _{CeO 2} , SrO, and SiO _{2 was changed as shown in Table 1.} Was prepared, the composition and crystal structure were identified in the same manner as in Example 1, and the element ratios of C (trivalent) and Ce (tetravalent) were confirmed.

<X-ray diffraction analysis>
The composition and crystal structure of the sintered body were specified by performing powder X-ray diffraction on the sintered sample and the heat-treated sample obtained in the above Examples and Comparative Examples. The X-ray diffraction pattern of the heat-treated sample of Example 3 is shown in FIG. As is clear from the X-ray diffraction pattern of FIG. 1, there are diffraction peaks (27 °, 31 °, 48 °, etc.) due to the apatite crystal structure in the range where the diffraction angle 2θ is in the range of 10 ° to 80 °. It can be seen that the composite oxide after the heat treatment of Example 3 has an apatite crystal structure. Further, by performing X-ray photoelectron spectroscopy of the sintered body, the ratio of trivalent and tetravalent cerium elements in the Ce element in the sintered body was confirmed. The results obtained were as shown in Table 1 below.

<Evaluation of conductivity>
A 150 nm-thick platinum film was formed on both sides of the obtained disk-shaped composite oxide by a sputtering method to form electrodes, and then the temperature was changed in a heating furnace, and the frequency was 0 with an impedance measuring device. . Complex impedance analysis was performed at 1 Hz to 32 MHz. The conductivity (S / cm) at 600 ° C. was determined from the total resistance components. The evaluation criteria for conductivity were as follows.
A: 1 × 10 ^-3 S / cm or more B: 0.5 × 10 ^-3 S / cm or more and 1 × 10 ^-3 S / cm or less C: 0.5 × 10 ^-3 S / cm or less The evaluation results are as shown in Table 1 below.

<Evaluation of electromotive force responsiveness>
<Example 5>
First, as a solid electrolyte, a disk-shaped apatite-type sintered body having a diameter of 20 mm (composition formula:) is similar to the method for preparing an apatite-type sintered body described in Example 1 of International Publication No. 2016/111101. La _9.83 Si _4.83 B _1.17 O _26.16 ) was prepared.
The sintered body obtained in Example 3 above was used as a sputtering target on both sides of the obtained apatite type sintered body (hereinafter referred to as LSBO layer), and the following film forming conditions were obtained by a high-frequency sputtering apparatus. A thin film mixture (precursor) was prepared as an intermediate layer having a thickness of 300 nm, and a laminate having a layer structure of "thin film mixture layer / LSBO layer / thin film mixture layer" was obtained.
・ Vacuum reaching pressure: 1.0 × 10 ^-4 Pa
・ Sputtering gas: Ar
・ Pressure during film formation: 1.0 Pa
・ Power density: 1.53 W / cm ²
・ Film formation time: 180 minutes ・ Film thickness: 300 nm

The laminate obtained as described above was sintered in a nitrogen atmosphere at 900 ° C. for 1 hour, and the thin film mixture (precursor) was sintered to form an intermediate layer. The layer structure was "intermediate". A sintered laminate that is a "layer / LSBO / intermediate layer" was obtained. Subsequently, Ag paste was applied to the surfaces on both sides of the obtained sintered laminate (that is, the surface of the intermediate layer) to form electrodes, and further sintering was performed at 900 ° C. in a nitrogen atmosphere to form a layer structure. A solid electrolyte type element which is "electrode / intermediate layer / LSBO layer / intermediate layer / electrode" was produced.

Next, using the solid electrolyte type element obtained as described above, an oxygen concentration cell (an oxygen concentration was prepared, one electrode was used as a reference electrode, and the other electrode was used as a detection electrode, and a potentiostat (Solartron) was used. The electromotive force was evaluated using (manufactured by the company). First, pretreatment was performed at 700 ° C. for 30 minutes in an atmospheric pressure atmosphere (oxygen concentration 20.9%), and then the evaluation temperatures were 600 ° C. and 500 ° C., respectively. In, the oxygen concentration on the reference electrode side was fixed to the atmospheric pressure atmosphere (oxygen concentration 20.9%), and the oxygen concentration on the detection electrode side was changed stepwise to 20%, 40%, and 60%. The presence or absence of the responsiveness of the electromotive force was confirmed from the electromotive force response curve (time change curve of the electromotive force). As a result, as shown in FIG. 2, the response of the electromotive force according to the change in the oxygen concentration on the detection electrode side. I was able to confirm that there is.

<Comparative example 4>
A solid electrolyte type device was produced in the same manner as in Example 5 except that the sintered body of Comparative Example 1 was used instead of the sintered body of Example 3 as the sintered body when forming the intermediate layer. The electromotive force responsiveness was evaluated. As a result, it could not be confirmed that there was a response of the electromotive force according to the change of the oxygen concentration on the detection electrode side.

Claims (10)

Composition _{formula: Ce x M y Si 6 O} z
(During the ceremony,
M is at least one element selected from the group consisting of Mg, Ca, Sr and Ba.
x is in the range of 6.0 ≤ x ≤ 9.6.
y is in the range of 0.4 ≦ y ≦ 4.0,
However, 8.0 ≦ (x + y) ≦ 10.0 is satisfied, and
z is in the range of (1.5x + y + 12) ≦ z ≦ (2x + y + 12). )
Represented by
In the composition formula, an apatite-type composite oxide in which the ratio of Ce (tetravalence) in the Ce element is 20 atm% or more. The apatite-type composite oxide according to claim 1, wherein M is Ca in the composition formula. The apatite-type composite oxide according to claim 1 or 2, wherein y is in the range of 0.8 ≦ y ≦ 3.8 in the composition formula. The element ratio is Ce: M: Si = x: y: 6 (where M is at least one element selected from the group consisting of Mg, Ca, Sr and Ba, 6.0 ≤ x ≤ 9.6. , 0.4 ≦ y ≦ 4.0, but 8.0 ≦ (x + y) ≦ 10.0 ) and the step of forming a mixture.
The mixture was sintered in an inert gas atmosphere, the composition _{formula: Ce x M y Si 6 O} z
( During the ceremony,
x is in the range of 6.0 ≤ x ≤ 9.6.
y is in the range of 0.4 ≦ y ≦ 4.0,
However, 8.0 ≦ (x + y) ≦ 10.0 is satisfied, and
z is in the range of (1.5x + y + 12) ≦ z ≦ (2x + y + 12) . )
And the process of making a sintered body with
A step of heat-treating the sintered body in an oxygen-presence atmosphere so that the ratio of Ce (tetravalence) in the Ce element is 20 atm% or more.
A method for producing an apatite-type composite oxide. The method according to claim 4 , wherein the sintering is performed at 700 to 1700 ° C. The method according to claim 4 or 5 , wherein the heat treatment is performed at 500 to 900 ° C. A solid electrolyte type element comprising a solid electrolyte and at least one electrode provided on the surface of the solid electrolyte.
A solid electrolyte type device in which the solid electrolyte is made of the apatite-type composite oxide according to any one of claims 1 to 3. Wherein the solid electrolyte has a multilayer structure, wherein at least one layer of a multilayer structure composed of the apatite type composite oxide, electrodes provided on the surface layer of the apatite-type composite oxide, in claim 7 The solid electrolyte type element described. A thin film made of the apatite-type composite oxide according to any one of claims 1 to 3. A sputtering target made of the apatite-type composite oxide according to any one of claims 1 to 3.

Images