JP2023164783A - Solid electrolyte and solid electrolyte bonded body - Google Patents

Abstract

To provide a solid electrolyte which enables reduction of the electric resistance of a device comprising the solid electrolyte, and a solid electrolyte bonded body comprising the solid electrolyte.SOLUTION: The solid electrolyte bonded body of the present invention is formed by bonding a solid electrolyte made of apatite-type composite oxide having oxide ion conductivity and having a value of I002/I004, which is the ratio of the peak intensity I002 of 002 to the peak intensity I004 of 004 obtained by X-ray diffraction measurement, of 0.3 or more and 0.8 or less, and a metal oxide intermediate layer. Preferably, the solid electrolyte is oriented along the c-axis. It is preferable that the metal oxide is made of cerium oxide including one or more elements selected from the group consisting of samarium, yttrium, gadolinium, and lanthanum.SELECTED DRAWING: Figure 1

Description

The present invention relates to a solid electrolyte and a solid electrolyte assembly. The solid electrolyte and solid electrolyte assembly of the present invention are used in various fields utilizing their oxide ion conductivity.

Various oxide ion conductive solid electrolytes are known. Such solid electrolytes are used in various fields, such as oxygen permeable elements, fuel cell electrolytes, and gas sensors. For example, Patent Document 1 describes an electrolyte-electrode assembly in which a solid electrolyte made of an apatite-type composite oxide is interposed between an anode side electrode and a cathode side electrode. An intermediate layer exhibiting isotropic oxide ion conduction is interposed between the cathode side electrode and the solid electrolyte. The intermediate layer consists of cerium oxide doped with samarium, yttrium, gadolinium or lanthanum. The solid electrolyte consists of La _x Si ₆ O _1.5X+12 (8≦X≦10). This document states that this electrolyte/electrode assembly improves the power generation performance of a solid oxide fuel cell.

Japanese Patent Application Publication No. 2013-51101

As described in Patent Document 1, various devices using solid electrolytes with oxide ion conductivity have been proposed, but when evaluating the entire device, the inherent oxide ion conductivity of the solid electrolyte is I couldn't say that I was bringing out the full potential. In particular, even if the solid electrolyte itself has high oxide ion conductivity, the electrical resistance at the interface between the solid electrolyte and the electrode may become high, and the electrical resistance of the device as a whole may become high.

Therefore, an object of the present invention is to provide a solid electrolyte that can reduce the electrical resistance of a device that includes a solid electrolyte, and a solid electrolyte assembly that includes the solid electrolyte.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention found that the above-mentioned problems can be solved by using an apatite-type composite oxide having a specific crystal structure as a solid electrolyte. The present invention was made based on this knowledge, and is composed of an apatite-type composite oxide having oxide ion conductivity, and the ratio of the peak intensity I ₀₀₂ of 002 to the peak intensity I 004 of ₀₀₄ obtained by X-ray diffraction measurement. The above problem has been solved by providing a solid electrolyte in which the value of I ₀₀₂ /I ₀₀₄ is 0.3 or more and 0.8 or less.

The present invention also provides a solid electrolyte assembly in which the solid electrolyte described above is joined to a metal oxide intermediate layer or a metal electrode layer.

FIG. 1 is a schematic diagram showing an embodiment of a device including a solid electrolyte of the present invention. FIG. 2 is a schematic diagram showing another embodiment of a device including the solid electrolyte of the present invention. FIG. 3 is a schematic diagram showing still another embodiment of a device including the solid electrolyte of the present invention.

The present invention will be described below based on its preferred embodiments. The solid electrolyte of the present invention is made of an apatite-type composite oxide having oxide ion conductivity. A solid electrolyte is a conductor in which oxide ions serve as carriers.

Examples of the apatite-type complex oxide include complex oxides containing lanthanum and silicon. This apatite-type composite oxide contains lanthanum (La), which is a trivalent element, silicon (Si), which is a tetravalent element, and oxygen (O), and has a composition of La _x Si ₆ O _{1. 5x+12} (x represents a number from 8 to 10) is preferable from the viewpoint of high oxide ion conductivity. The most preferable composition of this apatite type composite oxide is La _9.33 Si ₆ O ₂₆ . This composite oxide can be produced, for example, according to the method described in JP-A No. 2013-51101.

Another example of the apatite-type composite oxide is a composite oxide represented by the general formula (1): A _9.33+x [T _6.00-y M _y ]O _26.0+z . This composite oxide also has an apatite structure. A in the formula was selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr and Ba. One or more elements. T in the formula is an element containing Si or Ge or both. M in the formula is selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Ge, Zn, Sn, W and Mo. One or more elements. From the viewpoint of improving c-axis orientation, M is preferably one or more elements selected from the group consisting of B, Ge, and Zn.

From the viewpoint of increasing the degree of orientation and oxide ion conductivity, x in the formula is preferably -1.33 or more and 1.50 or less, more preferably 0.00 or more and 0.70 or less, and 0. More preferably, it is .45 or more and 0.65 or less. From the viewpoint of filling the T element position in the apatite crystal lattice, y in the formula is preferably 0.00 or more and 3.00 or less, more preferably 0.40 or more and 2.00 or less, and 0. More preferably, it is 40 or more and 1.00 or less. From the viewpoint of maintaining electrical neutrality within the apatite crystal lattice, z in the formula is preferably -5.00 or more and 5.20 or less, and -2.00 or more and 1.50 or less. is more preferable, and even more preferably -1.00 or more and 1.00 or less.

In the above formula, the ratio of the number of moles of A to the number of moles of T, in other words, (9.33+x)/(6.00-y) in the above formula is determined from the viewpoint of maintaining the spatial occupation rate in the apatite crystal lattice. , is preferably 1.33 or more and 3.61 or less, more preferably 1.40 or more and 3.00 or less, and even more preferably 1.50 or more and 2.00 or less.

Among the complex oxides represented by the above general formula (1), the complex oxide in which A is lanthanum, that is, the complex oxide represented by La _9.33+x [T _6.00-y M _y ]O _26.0+z If used, it is preferable from the viewpoint of further increasing oxide ion conductivity. Specific examples of complex oxides represented by La _9.33+x [T _6.00-y M _y ]O _26.0+z include La _9.33+x (Si _4.70 B _1.30 ) O _26.0+z and La _9.33+x (Si _4.70 Ge _1.30 ) O _26.0+z , La _9.33+x (Si _4.70 Zn _1.30 ) O _26.0+z , La _9.33+x (Si _4.70 W _1.30 ) O 26.0 _+z , La _9.33+x (Si _4.70 Sn _1.30 ) O _{26.0 +x} , La _9.33+x (Ge _4.70 B _1.30 )O _26.0+z , and the like. The composite oxide represented by the above general formula (1) can be produced, for example, according to the method described in US2018/183068A1.

Even when using any of the above-mentioned apatite-type composite oxides, the composite oxide containing lanthanum can effectively reduce the electrical resistance of the device containing the solid electrolyte of the present invention. Preferable from this point of view. Further, no matter which apatite type composite oxide is used, it is preferable that the composite oxide is oriented along the c-axis. Oriented along the c-axis means that when the apatite-type composite oxide is a polycrystalline substance, the crystal axes are aligned along the c-axis. Furthermore, when the apatite-type composite oxide exists in the form of a single crystal, its c-axis direction can be made to coincide with the conduction direction of oxide ions in the device.

When an apatite-type composite oxide is subjected to X-ray diffraction measurement, the value of I ₀₀₂ /I ₀₀₄ , which is the ratio of the peak intensity I 002 of ₀₀₂ to the peak intensity I 004 of ₀₀₄ obtained by the measurement, is 0.3. One of the characteristics is that it is 0.8 or less. Until now, when apatite-type composite oxides strongly oriented along the c-axis were measured by X-ray diffraction, the diffraction peak intensities other than 00x (x is an even number of 2 or more) were extremely small, and quantitative analysis was difficult. The problem was that it was difficult. However, the present inventor has found that the intensity ratio of the diffraction peaks of 002 and 004 strongly reflects the amount of defective sites, and furthermore, an apatite-type composite oxide whose intensity ratio is within a specific range has a strong relationship with the electrode layer. It has been found that the interfacial resistance is lowered and the electrical resistance of the device as a whole is lowered. In particular, when the apatite-type composite oxide contains lanthanum, if the composite oxide loses lanthanum while maintaining the apatite-type crystal structure, oxygen in the structure is also deleted in order to maintain the charge balance. The present inventor believes that when oxygen vacancies occur, the oxide ions move more easily, the conductivity of the oxide ions improves, and the interfacial resistance between the composite oxide and the electrode layer further decreases. Furthermore, since A other than lanthanum easily enters the same crystal site as lanthanum in the apatite-type composite oxide, it is thought that the same mechanism as described above occurs. In this manner, the present invention aims to improve oxide ion conductivity not due to the intermediate layer or electrode layer bonded to the solid electrolyte, but due to the crystal structure of the solid electrolyte itself.

As the amount of defect sites in the apatite-type composite oxide increases, the value of the ratio of I ₀₀₂ to I ₀₀₄ decreases, and the interfacial resistance between the apatite-type composite oxide and the electrode layer decreases. From this viewpoint, the value of the ratio of I ₀₀₂ to I ₀₀₄ is preferably 0.5 or more and 0.8 or less, and more preferably 0.5 or more and 0.75 or less.

The values of I ₀₀₂ and I ₀₀₄ are determined using X-ray diffraction. Specifically, the measurement can be performed using a point converging X-ray condensing mirror (CMF optical system) and a zero-dimensional detector. The peak intensity of X-ray diffraction in the present invention refers to an integrated intensity.

Regarding the peak intensity of this X-ray diffraction, in order to more accurately measure the amount of defect sites in the apatite crystal structure, the peak intensity ratio of 002 and 004, which gives a higher X-ray diffraction intensity, was selected as an index. It was decided to. Note that the X-ray diffraction peak positions of 002 and 004 in the apatite crystal structure can be uniquely determined from a known crystal database or the like.

In order to make the value of the ratio of I ₀₀₂ to I ₀₀₄ satisfy the above-mentioned range, it is preferable to form a defect site in the apatite-type composite oxide. In order to form a defect site, it is advantageous to form a film of a different composition adjacent to the apatite-type composite oxide, for example, and to remove constituent elements, particularly lanthanum, from the crystal structure by annealing the film. was found as a result of the inventor's study. In this case, it is necessary to remove constituent elements such as lanthanum while maintaining the apatite crystal structure. For this purpose, a film (hereinafter also referred to as "La absorption film") that allows lanthanum to diffuse or solidly dissolve lanthanum is laminated on the surface of the apatite-type composite oxide. Then, it is preferable that lanthanum in the apatite-type composite oxide is diffused or solid-dissolved in the La absorption film by annealing at a high temperature of 700° C. or higher to obtain an apatite-type composite oxide lacking lanthanum. The La absorption film may then be removed by a predetermined means.

The solid electrolyte of the present invention can be used as is or in the form of a device in combination with other members, depending on its specific use. An example of such a device is shown in FIG. The device shown in FIG. 1 is a solid electrolyte assembly 10 including the solid electrolyte of the present invention. This solid electrolyte assembly 10 will be explained below.

As shown in FIG. 1, the solid electrolyte assembly 10 includes a layer 11 made of the solid electrolyte described above (hereinafter referred to as "solid electrolyte layer"). An intermediate layer 12 laminated in contact with the solid electrolyte layer 11 is bonded to one surface of the solid electrolyte layer 11 . In the embodiment shown in FIG. 1, the solid electrolyte layer 11 and the intermediate layer 12 are in direct contact with each other, and no other layer is interposed between them. The intermediate layer 12 is made of a material having oxide ion conductivity and electronic conductivity.

From the viewpoint of effectively reducing the electrical resistance of the solid electrolyte assembly 10, the thickness of the solid electrolyte layer 11 is preferably 10 nm or more and 1000 μm or less, more preferably 50 nm or more and 700 μm or less, and 100 nm or more and 500 μm or less. It is more preferable that The thickness of the solid electrolyte layer 11 can be measured using, for example, a stylus level difference gauge, a caliper, or an electron microscope.

As shown in FIG. 1, the solid electrolyte assembly 10 has a metal electrode layer 13 bonded to one of the two surfaces of the solid electrolyte layer 11, the surface opposite to the surface on which the intermediate layer 12 is disposed. It's okay. By arranging the solid electrolyte layer 11, intermediate layer 12, and metal electrode layer 13 in this order, a device 20 made of the solid electrolyte assembly 10 is configured. In the embodiment shown in FIG. 1, the solid electrolyte layer 11 and the metal electrode layer 13 are in direct contact with each other, and no other layer is interposed between them.

The intermediate layer 12 includes a metal oxide. The intermediate layer 12 may consist only of metal oxides or may contain metal oxides and other substances. The intermediate layer 12 is formed for the purpose of smoothly transferring oxide ions to and from the solid electrolyte layer 11. According to this embodiment, due to the fact that the solid electrolyte having the above-described specific crystal structure is used as the solid electrolyte layer 11, the solid electrolyte layer 11 and the intermediate layer 12 are different from each other regardless of the type of the intermediate layer 12. The interfacial resistance between the two layers can be lowered, and oxide ions can be exchanged more smoothly.

The intermediate layer 12 is preferably made of a metal oxide and has oxide ion conductivity. As the intermediate layer 12, for example, cerium oxide containing one or more elements selected from the group consisting of samarium, yttrium, gadolinium, and lanthanum (hereinafter, these elements are also referred to as "doping elements" for convenience). can be used. In this case, the content of the doping element is preferably 0.1 mol% or more and 0.5 mol% or less expressed as M/(M+Ce)×100 (M represents the number of moles of the doping element), It is more preferably 0.15 mol% or more and 0.4 mol% or less, even more preferably 0.2 mol% or more and 0.3 mol% or less.

Bismuth oxide can also be used as the intermediate layer 12. Examples of bismuth oxides include bismuth (III) oxide and composite oxides of bismuth and other metal elements. Examples of other metal elements include one or more rare earth elements. Examples of rare earth elements include lanthanum, gadolinium, yttrium, erbium, ytterbium, and dysprosium. In particular, if the intermediate layer 12 is configured to include a composite oxide of bismuth and lanthanum, gadolinium, or yttrium, the electrical resistance between the solid electrolyte layer 11 and the intermediate layer 12 can be effectively reduced. Preferable from this point of view. Furthermore, this composite oxide is preferably represented by (Ln _{m Bin} ) ₂ O ₃ . In the formula, Ln represents a rare earth element. The sum of m and n is 1, and n>0. Moreover, it is preferable that m is 0.1 or more and 0.4 or less.

A mixed conductor having oxide ion conductivity and electronic conductivity can also be used as the intermediate layer 12. A mixed conductor is a substance that has two conductivities, oxide ion conductivity and electronic conductivity, that is, mixed conductivity. In particular, from the viewpoint of achieving lattice matching in a plane perpendicular to the orientation direction at the interface between the solid electrolyte layer 11 and the intermediate layer 12, the material constituting the intermediate layer 12 is preferably a perovskite oxide. In particular, when the material constituting the solid electrolyte layer 11 is represented by the general formula (1) described above, when the material constituting the intermediate layer 12 is a perovskite oxide, the above lattice matching can be successfully achieved. I can plan well.

In particular, it is preferable to use a material represented by the general formula (2): ABO ₃ as the material constituting the intermediate layer 12 from the viewpoint of further improving oxide ion conductivity. In the formula, A preferably uses one or more metal elements selected from, for example, La, Sr, Ba, and Ca, and a particularly preferable metal element is at least one of La and Sr. B is a transition metal element, and it is preferable to use one or more metal elements selected from Co, Ni, Mn, Cr, Ti, Fe, and Cu, and particularly preferable metal elements are Co and Ni. At least one kind. In particular, the material represented by general formula (2) is preferably a composite oxide containing La, Sr, Co, and Ni.

Among the complex oxides represented by general formula (2), particularly preferred are those represented by La _0.6 Sr _0.4 Co _0.9 Ni _0.1 O _3-δ .

The intermediate layer 12 made of a composite oxide represented by the general formula (2) can be formed on one surface of the solid electrolyte layer 11 using, for example, various thin film forming methods. Examples of the thin film forming method include a physical vapor deposition method and a chemical vapor deposition method. Among these, the use of the physical vapor deposition method allows the intermediate layer 12 to be formed more successfully. Among physical vapor deposition methods, it is particularly preferable to use PLD (Pulsed Laser Deposition) method.

No matter which of the materials that constitute the intermediate layer 12 are mentioned above, the material that constitutes the solid electrolyte layer 11 and the material that constitutes the intermediate layer 12 are both the same as those of the solid electrolyte layer 11 and the intermediate layer 12. Uniaxial orientation along the stacking direction is effective from the viewpoint of reducing interfacial resistance. In order to uniaxially align the material constituting the solid electrolyte layer 11 and the material constituting the intermediate layer 12 along the lamination direction, for example, while heating the solid electrolyte layer 11 serving as the substrate to a predetermined temperature, The thin film of the intermediate layer 12 may be formed on the solid electrolyte layer 11 using physical vapor deposition or chemical vapor deposition in an atmosphere with a controlled oxygen partial pressure, and may be epitaxially grown locally. Further, the uniaxially oriented thin film of the intermediate layer 12 can also be formed on the solid electrolyte layer 11 using atomic layer deposition (ALD). However, the method is not limited to these methods.

Whether or not the material constituting the solid electrolyte layer 11 and the material constituting the intermediate layer 12 are both uniaxially oriented can be determined from cross-sectional observation using a TEM (transmission electron microscope) of the bonding interface. . The lattice constant and interplanar spacing of the solid electrolyte layer 11 and the intermediate layer 12 can be calculated from the diffraction pattern obtained by performing X-ray diffraction measurement while rocking.

No matter which of the materials mentioned above is used for forming the intermediate layer 12, if the intermediate layer 12 has a predetermined thickness, the electrical resistance between the intermediate layer 12 and the solid electrolyte layer 11 can be effectively reduced. Specifically, the thickness of the intermediate layer 12 bonded to the solid electrolyte layer 11 along the stacking direction is preferably 80 nm or more, more preferably 100 nm or more, and even more preferably 100 nm or more and 1000 nm or less. . The thickness of the intermediate layer 12 can be measured using a stylus type step meter or an electron microscope.

The metal electrode layer 13 formed on the opposite side of the intermediate layer 12 with the solid electrolyte layer 11 in between is easy to form and has advantages such as high catalytic activity, so it is composed of a platinum group element. It is preferable that Examples of platinum group elements include platinum, ruthenium, rhodium, palladium, osmium, and iridium. These elements can be used alone or in combination of two or more. Further, as the metal electrode layer 13, a cermet containing a platinum group element can also be used.

The solid electrolyte assembly 10 and device 20 of the embodiment shown in FIG. 1 can be suitably manufactured, for example, by the method described below. First, solid electrolyte layer 11 is manufactured by a known method. For manufacturing, for example, the method described in JP 2013-51101 A and US 2018/183068A1 can be adopted.

Next, intermediate layer 12 is formed on one of the two surfaces of solid electrolyte layer 11 . Various thin film forming methods can be used to form the intermediate layer 12. As one of the thin film forming methods, for example, the above-mentioned PLD method can be used. Specifically, in order to uniaxially align both the material constituting the solid electrolyte layer 11 and the material constituting the intermediate layer 12 along the stacking direction of the solid electrolyte layer 11 and the intermediate layer 12, When forming the intermediate layer 12 on one surface of the solid electrolyte layer 11 using the PLD method described above, the solid electrolyte layer 11 may be heated to a predetermined temperature. It is preferable to set the heating temperature to, for example, 600° C. or higher and 700° C. or lower because uniaxial orientation can be achieved more successfully.

After forming the intermediate layer 12 in this manner, a metal electrode layer 13 is formed on the surface of the solid electrolyte layer 11 opposite to the surface on which the intermediate layer 12 is formed. For forming the metal electrode layer 13, a paste containing particles of a platinum group metal is used, for example. The paste is applied to the surface of the solid electrolyte layer 11 to form a coating film, and the coating film is fired to form an electrode made of a porous body. The firing conditions may be a temperature of 600° C. or more and a time of 30 minutes or more and 120 minutes or less. The atmosphere can be an oxygen-containing atmosphere such as air.

The desired solid electrolyte assembly 10 and device 20 are obtained by the above method. The device 20 thus obtained can be suitably used as an oxygen permeable element, various gas sensors including oxygen sensors, water vapor electrolysis or solid electrolyte fuel cells, etc. by utilizing its high oxide ion conductivity. It will be done. Whatever the application of the device 20, it is advantageous to use the intermediate layer 12 as a cathode, ie, as the pole at which the reduction reaction of oxygen gas takes place. For example, when the device 20 is used as an oxygen permeable element, the metal electrode layer 13 is connected to the anode of a DC power source, and the intermediate layer 12 is connected to the cathode of the DC power source, so that the intermediate layer 12 and the metal electrode layer 13 are connected to each other. A predetermined DC voltage is applied between the two. As a result, oxygen receives electrons on the intermediate layer 12 side and oxide ions are generated. The generated oxide ions move through the solid electrolyte layer 11 and reach the metal electrode layer 13. The oxide ions that have reached the metal electrode layer 13 release electrons and become oxygen gas. Such a reaction allows the solid electrolyte layer 11 to transmit oxygen gas contained in the atmosphere on the intermediate layer 12 side to the metal electrode layer 13 side through the solid electrolyte layer 11. Note that, if necessary, a current collecting layer made of a conductive material such as platinum may be formed on at least one of the surface of the intermediate layer 12 and the surface of the metal electrode layer 13.

The applied voltage is preferably set to 0.1 V or more and 4.0 V or less from the viewpoint of increasing the amount of oxygen gas permeation. When applying a voltage between the two electrodes, it is preferable that the oxide ion conductivity of the solid electrolyte layer 11 is sufficiently high. For example, it is preferable that the oxide ion conductivity is 1.0×10 ⁻³ S/cm or more expressed in conductivity. For this purpose, it is preferable to maintain the solid electrolyte layer 11 or the entire device 20 at a predetermined temperature. Although this holding temperature depends on the material of the solid electrolyte layer 11, it is generally preferable to set it in a range of 300°C or more and 600°C or less. By using the device 20 under this condition, oxygen gas contained in the atmosphere on the intermediate layer 12 side can be permeated through the solid electrolyte layer 11 to the metal electrode layer 13 side.

When the device 20 is also used as a limiting current type oxygen sensor, the oxide ions generated on the intermediate layer 12 side move to the metal electrode layer 13 side via the solid electrolyte layer 11, so that the current occurs. Since the current value depends on the oxygen gas concentration on the intermediate layer 12 side, the oxygen gas concentration on the intermediate layer 12 side can be measured by measuring the current value.

Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, in the embodiment, the intermediate layer 12 is disposed only on one surface of the solid electrolyte layer 11, but instead, as shown in FIG. An intermediate layer 12' may also be provided. When a separate intermediate layer 12' is disposed on the surface of the solid electrolyte layer 11 facing the intermediate layer 12, each intermediate layer 12, 12' may be the same or different. good. In this case, the material constituting the solid electrolyte layer 11, the material constituting one intermediate layer 12, and the material constituting the other intermediate layer 12' are all uniaxially oriented along their lamination direction. It is preferable that

Further, instead of forming the intermediate layers 12, 12' on each surface of the solid electrolyte layer 11, metal electrode layers 13, 13' may be formed as shown in FIG. Even in this case, the electrical resistance of the entire device 20 can be reduced. Each metal electrode layer 13, 13' may be the same or different.

Hereinafter, the present invention will be explained in more detail with reference to Examples. However, the scope of the invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass".

[Example 1]
La ₂ O ₃ powder and SiO ₂ powder were blended at a molar ratio of 1:1, ethanol was added, and the mixture was mixed in a ball mill. The mixture was dried, ground in a mortar, and calcined at 1650° C. for 3 hours in an air atmosphere using a platinum crucible. Ethanol was added to this baked product, and it was ground in a ball mill to obtain a baked powder. This fired powder was placed in a 20 mmφ molding machine and uniaxially molded by applying pressure from one direction. Further, cold isostatic pressing (CIP) was performed at 700 MPa for 1 minute to form pellets. This pellet-shaped molded body was heated in the atmosphere at 1600° C. for 3 hours to obtain a pellet-shaped sintered body. When this sintered body was subjected to powder X-ray diffraction measurement and chemical analysis, it was confirmed that it had a La ₂ SiO ₅ structure having an apatite type crystal structure.

800 mg of the obtained pellets and 140 mg of B ₂ O ₃ powder were placed in a sagger with a lid. The pellets and B ₂ O ₃ powder were heated in the air at 1550° C. (furnace atmosphere temperature) for 50 hours using an electric furnace. By this heating, B ₂ O ₃ vapor was generated in the sagger, and the B ₂ O ₃ vapor was caused to react with the pellets, thereby obtaining the intended solid electrolyte layer 11 . This solid electrolyte layer 11 has x=0.50, y=1.17, and z=0.16 in La _9.33+x [Si _6.00-y B _y ]O _26.0+z , and La and Si The molar ratio of was 2.04. Further, the thickness measured using a caliper was 350 μm. Hereinafter, this compound will be abbreviated as "LSBO".

[Manufacture of La absorption film]
The Bi ₂ O ₃ powder was placed in a 50 mmφ molding machine and uniaxially molded by applying pressure from one direction, followed by hot press sintering. The sintering conditions were a nitrogen gas atmosphere, a pressure of 30 MPa, a temperature of 600° C., and a duration of 3 hours to obtain a target for sputtering. Using this target, sputtering was performed on both sides of the solid electrolyte layer 11 made of LSBO to a thickness of 300 nm by a high frequency sputtering method. The sputtering conditions were an RF output of 30 W and an argon gas pressure of 0.8 Pa. After completion of sputtering, annealing was performed at 750° C. for 1 hour in the air. As a result of this annealing, La in the solid electrolyte was diffused toward the Bi ₂ O ₃ layer (La absorption layer) side, and a La-deficient LSBO was formed. Next, an operation was performed to remove the layer in which La was absorbed from this solid electrolyte. Specifically, the _three Bi ₂ O layers in which La was absorbed were completely removed using a precision polishing device. The thickness of the La-deficient LSBO was then measured using a caliper and was 340 μm.

[Example 2]
A La-deficient LSBO was produced in the same manner as in Example 1, except that the La absorption layer was annealed at 800° C. for 1 hour.

[Example 3]
A La-deficient LSBO was produced in the same manner as in Example 1, except that the La absorption layer was annealed at 850° C. for 1 hour.

[Comparative example 1]
A solid electrolyte was produced in the same manner as in Example 1, except that the La absorption layer was not formed and therefore annealing was not performed.

[Rating 1]
The solid electrolytes obtained in Examples and Comparative Examples were subjected to XRD measurement using the method described below to determine the value of I ₀₀₂ /I ₀₀₄ . Further, the conductivity of oxide ions was measured by the method described below. The results are shown in Table 1 below.

[XRD measurement]
Measurement was performed under the following conditions using a fully automatic multi-purpose X-ray diffraction device SmartLab manufactured by Rigaku Corporation.
Tube voltage: 40kV
Tube current: 30mA
X-ray source: CuKα
Input optical element: confocal mirror (CMF)
Incidence side slit configuration: Collimator size 1.4mm x 1.4mm
Light receiving side slit configuration: Parallel slit analyzer 0.114deg, light receiving slit 20mm
Detector: Scintillation counter Measurement range: 2θ=20~60deg
Step width: 0.01deg
Scan speed: 1 deg/min Analysis was performed using Rigaku Co., Ltd.'s PDXL2. The peak intensities (integrated intensities) of 002 and 004 were obtained by selecting a straight line connecting the end points to the background and a segmented pseudo-Voigt function for the peak shape, and performing profile fitting. As described above, the 002 peak and the 004 peak are c-axis oriented, and therefore are independent peaks that do not overlap with peaks on other planes. If there is an overlap with a peak derived from another phase, which is expected when the device has a multilayer structure, the peak intensity can be resolved in the same way as general XRD data analysis, so only the peak intensities of 002 and 004 can be obtained. be able to.

[Measurement of oxide ion conductivity]
Electrodes were formed by forming platinum films with a thickness of 150 nm on both sides of the solid electrolyte using a sputtering method. This solid electrolyte was placed in a heating furnace, and complex impedance analysis of the solid electrolyte was performed while changing the temperature of the heating furnace. An impedance measuring device was used for the analysis, and the frequency was set at 0.1 Hz to 32 MHz. Oxide ion conductivity (S/cm) was determined from the total resistance component (intragrain resistance + grain boundary resistance). Table 1 shows the oxide ion conductivity at 600°C.

As is clear from the results shown in Table 1, the solid electrolytes obtained in each example in which the value of I ₀₀₂ /I ₀₀₄ was within a specific range had a conductivity about 5 times or more compared to the solid electrolyte of the comparative example. It can be seen that the effect of improving oxide ion conductivity is high.

[Example 4]
Intermediate layers 12 made of Bi ₂ O ₃ containing yttrium were formed on both sides of the solid electrolyte obtained in Example 1. A target manufactured by the following method was used to form the intermediate layer 12. Using this target, sputtering was performed on both sides of the solid electrolyte to form an intermediate layer. After forming the intermediate layer, heating was performed at 700° C. for 1 hour to produce solid electrolyte assembly 10.

[Manufacture of targets]
Predetermined amounts of Y ₂ O ₃ powder and Bi ₂ O ₃ powder were blended, ethanol was added, and they were mixed in a ball mill. The mixture was dried, ground in a mortar, and calcined in an alumina crucible at 700° C. for 3 hours in an air atmosphere. Ethanol was added to this fired product and the mixture was ground in a planetary ball mill to obtain a fired powder. This fired powder was placed in a 50 mm diameter molding machine and uniaxially molded by applying pressure from one direction, followed by hot press sintering. The sintering conditions were a nitrogen gas atmosphere, a pressure of 30 MPa, a temperature of 600° C., and 3 hours. In this way, a target for sputtering was obtained.

[Example 5]
In place of the target used in Example 4, a target made of cerium oxide containing samarium was used. This target was manufactured in the same manner as the target used in Example 4. Using this target, an intermediate layer 12 made of cerium oxide containing samarium was manufactured in the same manner as in Example 4. In this way, the solid electrolyte assembly 10 was manufactured.

[Comparative example 2]
An intermediate layer made of cerium oxide containing samarium was formed on both sides of the solid electrolyte obtained in Comparative Example 1. The intermediate layer was formed in the same manner as in Example 5.

[Measurement of current density]
The electrical resistance of the solid electrolyte assemblies obtained in Examples 4 and 5 and Comparative Example 2 was measured. Measurements were performed at 600°C. A DC voltage of 1 V was applied between the intermediate layers in the atmosphere, and the current density was calculated from the obtained current value. The results are shown in Table 2.

As is clear from the results shown in Table 2, the solid electrolyte assembly in which the intermediate layer is provided in the solid electrolyte whose I ₀₀₂ /I ₀₀₄ value falls within a specific range is about 7 times as strong as the solid electrolyte assembly of the comparative example. It can be seen that higher current density values can be obtained.

According to the present invention, a solid electrolyte that can reduce the electrical resistance of a device provided with a solid electrolyte is provided. Further, according to the present invention, a solid electrolyte assembly with low electrical resistance is provided.

Claims (7)

It is made of an apatite-type composite oxide having oxide ion conductivity, and the value of I ₀₀₂ /I ₀₀₄ , which is the ratio of the peak intensity I 002 of 002 to the peak intensity I ₀₀₄ of ₀₀₄ obtained by X-ray diffraction measurement, is 0.3. A solid electrolyte assembly formed by joining a solid electrolyte having a particle diameter of 0.8 or less and an intermediate layer of a metal oxide,
The composite oxide has the general formula: A _9.33+x [T _6.00-y M _y ]O _26.0+z (A in the formula is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, One or more elements selected from the group consisting of Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr and Ba.T in the formula is Si or Ge or both. M in the formula is Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Ge, Zn, Sn, One or more elements selected from the group consisting of W and Mo.), x in the formula is a number from -1.33 to 1.50, and y in the formula is 0. is a number of .00 or more and 2.00 or less, z in the formula is a number of -5.00 or more and 5.20 or less, and the ratio of the number of moles of A to the number of moles of T is 1.33 or more and 3.61 A solid electrolyte assembly containing the following composite oxide. The solid electrolyte assembly according to claim 1, wherein the solid electrolyte is oriented along the c-axis. The solid electrolyte assembly according to claim 1 or 2, wherein the metal oxide is made of cerium oxide containing one or more elements selected from the group consisting of samarium, yttrium, gadolinium, and lanthanum. The solid electrolyte assembly according to any one of claims 1 to 3, wherein the metal oxide is an oxide of bismuth. The solid electrolyte assembly according to any one of claims 1 to 4, wherein the metal oxide is a mixed conductor having oxide ion conductivity and electronic conductivity. 6. An intermediate layer, which is the same as or different from the intermediate layer, is disposed on a surface of the solid electrolyte assembly opposite to the surface on which the intermediate layer is disposed. Solid electrolyte conjugate. The solid electrolyte assembly according to any one of claims 1 to 6, which is used as an oxygen permeable element, a gas sensor, or a solid electrolyte fuel cell.

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