TWI809118B - Solid electrolyte and solid electrolyte junction - Google Patents

Abstract

An object of the present invention is to provide a solid electrolyte capable of reducing the resistance of a device having a solid electrolyte. The solid electrolyte of the present invention includes 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 is I The value of ₀₀₂ /I ₀₀₄ is not less than 0.3 and not more than 0.8. The solid electrolyte is preferably aligned to the c-axis. Also disclosed is a solid electrolyte assembly in which the above-mentioned solid electrolyte is bonded to an intermediate layer of a metal oxide or a metal electrode layer. The aforementioned metal oxide is preferably cerium oxide containing one or two or more elements selected from the group consisting of samarium, yttrium, gadolinium and lanthanum.

Description

Solid electrolyte and solid electrolyte junction

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 the ion conductivity of the oxide.

Various oxide ion conductive solid electrolytes are known. Such a solid electrolyte is used in various fields such as an oxygen permeable element, an electrolyte of a fuel cell, and a gas sensor. For example, Patent Document 1 describes an electrolyte and an electrode assembly in which a solid electrolyte containing an apatite-type composite oxide is interposed between an anode-side electrode and a cathode-side electrode. Between the cathode side electrode and the solid electrolyte, an intermediate layer showing isotropic oxide ion conduction is inserted. The intermediate layer comprises cerium oxide doped with samarium, yttrium, gadolinium or lanthanum. The solid electrolyte contains La _x Si ₆ O _{1.5X + 12} (8≦X≦10). This document describes that the power generation performance of the solid oxide fuel cell is improved by the electrolyte and the electrode assembly. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2013-51101

As described in Patent Document 1, although various devices using solid electrolytes with oxide ion conductivity are disclosed, it cannot be said that the original oxide ion conductivity of solid electrolytes is fully utilized when evaluating the device as a whole. . In particular, even when the oxide ion conductivity of the solid electrolyte itself is high, the resistance at the interface between the solid electrolyte and the electrodes may become high, and the resistance of the device as a whole may become high.

Therefore, an object of the present invention is to provide a solid electrolyte capable of reducing the resistance of a device including the solid electrolyte, and a solid electrolyte assembly including the solid electrolyte.

In order to solve the above-mentioned problems, the inventors of the present invention conducted earnest studies, and as a result, 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 completed based on this knowledge, and solves the above-mentioned problems by providing a solid electrolyte comprising an apatite-type composite oxide having oxide ion conductivity and obtained by X-ray diffraction measurement. The ratio of the peak intensity I 002 of ₀₀₂ to the peak intensity I ₀₀₄ of 004, that is, the value of I ₀₀₂ /I ₀₀₄ is 0.3 to 0.8.

Also, the present invention provides a solid electrolyte assembly in which the above-mentioned solid electrolyte is bonded to an intermediate layer of a metal oxide or a metal electrode layer.

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

As an apatite type composite oxide, the composite oxide containing lanthanum and silicon is mentioned, for example. This apatite-type composite oxide contains lanthanum (La) as a trivalent element, silicon (Si) as a tetravalent element, and oxygen (O), and its composition is La _x Si ₆ O _{1.5x + 12} (x represents a number from 8 to 10) is preferable in terms of high oxide ion conductivity. The optimum composition of the 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-2013-51101.

As another example of the apatite-type composite oxide, a composite oxide represented by the general formula (1): A _{9.33 + x} [T _6.00-y M _y ]O _26.0+z can be cited. This composite oxide also has an apatite structure. A in the formula is 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 contains elements of 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 alignment, M is preferably one or two or more elements selected from the group consisting of B, Ge, and Zn.

From the viewpoint of improving the degree of alignment and oxide ion conductivity, x in the formula is preferably -1.33 to 1.50, more preferably 0.00 to 0.70, more preferably 0.45 to 0.65. From the viewpoint of filling the T element position in the apatite-type lattice, y in the formula is preferably from 0.00 to 3.00, more preferably from 0.40 to 2.00, and more preferably from 0.40 to 1.00. From the viewpoint of maintaining electrical neutrality in the apatite lattice, z in the formula is preferably -5.00 to 5.20, more preferably -2.00 to 1.50, and more preferably -1.00 to 1.00.

In the above formula, the ratio of the mole number of A to the mole number of T, in other words, (9.33+x)/(6.00-y) in the above formula maintains the ratio of the space occupancy rate in the apatite lattice. From a viewpoint, it is preferably not less than 1.33 and not more than 3.61, more preferably not less than 1.40 and not more than 3.00, more preferably not less than 1.50 and not more than 2.00.

If A is a composite oxide of lanthanum in the composite oxide represented by the above general formula (1), that is, a composite oxide represented by La _{9.33 + x} [T _6.00-y My _] O _26.0+z , then the oxidation It is preferable from the viewpoint of further improving ion conductivity. Specific examples of the composite oxide represented by La _{9.33 + x} [T _6.00-y My _] O _26.0+z include: La _9.33+x (Si _4.70 B _1.30 )O _26.0+z , 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 , etc. The composite oxide represented by the above general formula (1) can be produced, for example, according to the method described in US2018/183068A1.

In the case of using any of the above as the apatite-type composite oxide, the composite oxide preferably contains lanthanum in terms of being able to effectively reduce the resistance of a device including the solid electrolyte of the present invention. Also, when any apatite-type composite oxide is used, it is preferable that the composite oxide is aligned on the c-axis. Aligning to the c-axis means that when the apatite-type composite oxide is polycrystalline, the crystallographic axes are aligned along the c-axis. Furthermore, when the apatite-type composite oxide exists as a single crystal, the c-axis direction can be aligned with the conduction direction of oxide ions in the device.

The apatite-type composite oxide has one of the following characteristics: when it is measured by X-ray diffraction, the ratio of the peak intensity I ₀₀₂ of 002 to the peak intensity I 004 of ₀₀₄ obtained by the measurement is I ₀₀₂ The value of / _I004 is not less than 0.3 and not more than 0.8. So far, if X-ray diffraction measurement is performed on apatite-type composite oxides that are strongly aligned to the c-axis, the intensity of diffraction peaks other than 00x (x represents an even number greater than 2) is very small, and quantitative analysis is difficult. topic. However, the present inventors found that the intensity ratio of the diffraction peaks of 002 and 004 strongly reflects the amount of the defect, and further found that the interface between the apatite-type composite oxide and the electrode layer where the intensity ratio is in a specific range The resistance becomes lower, thereby reducing the resistance of the device as a whole. Especially when the apatite-type composite oxide contains lanthanum, if the composite oxide maintains the apatite-type crystal structure and lanthanum is deficient, oxygen in the structure is also deficient in order to maintain charge balance. The inventors of the present invention believe that if oxygen deficiency occurs, the oxide ions move easily, the conductivity of the oxide ions increases, and the interface resistance between the composite oxide and the electrode layer further decreases. Also, A other than lanthanum is considered to exhibit the same mechanism as above because it easily enters the same crystal site as lanthanum in the apatite-type composite oxide. Thus, the present invention improves oxide ion conductivity due to the crystalline structure of the solid electrolyte itself, not due to the intermediate layer or electrode layer bonded to the solid electrolyte.

The more defect sites in the apatite composite oxide, the smaller the ratio of I ₀₀₂ to I ₀₀₄ , and the lower the interface resistance between the apatite composite oxide and the electrode layer. From this point of view, the value of the ratio of I ₀₀₂ to I ₀₀₄ is preferably from 0.5 to 0.8, more preferably from 0.5 to 0.75.

The values of I ₀₀₂ and I ₀₀₄ were determined using X-ray diffraction method. Specifically, it can be measured using a point-converging X-ray condenser (CMF optical system) and a 0-dimensional detector. The peak intensity of X-ray diffraction referred to in the present invention refers to the integrated intensity.

Regarding the peak intensity of X-ray diffraction, in order to more accurately measure the amount of defects in the apatite crystal structure, the peak intensity ratio of 002 and 004, which obtains higher X-ray diffraction intensity, was selected as an index. Furthermore, the X-ray diffraction peak positions of 002 and 004 in the apatite crystal structure can be uniquely determined based on known crystal databases and the like.

In order to make the ratio of I ₀₀₂ to I ₀₀₄ satisfy the above range, it is preferable to form a defect in the apatite-type composite oxide. As a result of research by the inventors of the present invention, it has been found that, for example, forming a film of a different composition adjacent to an apatite-type composite oxide and annealing the film can remove constituent elements, especially lanthanum, from the crystal structure, which is advantageous. at the site of the defect. In this case, it is necessary to remove constituent elements such as lanthanum while maintaining the apatite crystal structure. For this purpose, a film capable of diffusing or dissolving lanthanum (hereinafter also referred to as "La absorbing film") is laminated on the surface of the apatite-type composite oxide. Furthermore, it is preferable to anneal at a high temperature of 700° C. or higher to diffuse or dissolve lanthanum in the apatite-type composite oxide in the La absorption film, thereby obtaining a lanthanum-deficient apatite-type composite oxide. Thereafter, the La absorbing film can also be removed by a predetermined method.

The solid electrolyte of the present invention can be used directly according to its specific use, or can be used in the state of a device combined with other components. Fig. 1 shows an example of such a device. The device shown in FIG. 1 is a solid electrolyte assembly 10 including the solid electrolyte of the present invention. Hereinafter, the solid electrolyte assembly 10 will be described.

As shown in FIG. 1 , a solid electrolyte assembly 10 includes a layer (hereinafter referred to as “solid electrolyte layer”) 11 containing the above-mentioned solid electrolyte. 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 is in direct contact with the intermediate layer 12 without intervening other layers. The intermediate layer 12 includes a material having oxide ion conductivity and electron conductivity.

From the viewpoint of effectively reducing the resistance of the solid electrolyte assembly 10, the thickness of the solid electrolyte layer 11 is preferably from 10 nm to 1000 μm, more preferably from 50 nm to 700 μm, more preferably from 100 nm to 500 μm the following. The thickness of the solid electrolyte layer 11 can be measured using, for example, a stylus profiler, a vernier caliper, or an electron microscope.

As shown in FIG. 1 , the solid electrolyte assembly 10 may have the metal electrode layer 13 bonded to the surface opposite to the surface on which the intermediate layer 12 is disposed, of the two surfaces of the solid electrolyte layer 11 . The solid electrolyte layer 11 , the intermediate layer 12 , and the metal electrode layer 13 are arranged in this order, thereby forming a device 20 including the solid electrolyte assembly 10 . In the embodiment shown in FIG. 1 , the solid electrolyte layer 11 is in direct contact with the metal electrode layer 13 , and no other layers are interposed between them.

The intermediate layer 12 is composed of a metal oxide. The intermediate layer 12 contains only metal oxide, or contains metal oxide 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, since the solid electrolyte having the above-mentioned specific crystal structure is used as the solid electrolyte layer 11, regardless of the type of the intermediate layer 12, the interface resistance between the solid electrolyte layer 11 and the intermediate layer 12 can be reduced, and more The transfer and reception of oxide ions is carried out smoothly.

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

Bismuth oxide can also be used as the intermediate layer 12 . As an oxide of bismuth, bismuth (III) oxide or the composite oxide of bismuth and another metal element is mentioned, for example. As other metal elements, for example, one or more kinds of rare earth elements can be cited. Examples of rare earth elements include lanthanum, gadolinium, yttrium, erbium, ytterbium, and dysprosium. In particular, the intermediate layer 12 is preferably a composite oxide containing bismuth and lanthanum, gadolinium, or yttrium from the viewpoint of being able to effectively reduce the resistance between the solid electrolyte layer 11 and the intermediate layer 12 . Furthermore, the 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. Also, m is preferably from 0.1 to 0.4.

A mixed conductor having oxide ion conductivity and electron conductivity can also be used as the intermediate layer 12 . The mixed conductivity system is a substance having two kinds of conductivities of oxide ion conductivity and electron conductivity, that is, mixed conductivity. In particular, the material constituting the intermediate layer 12 is preferably a perovskite-type oxide from the viewpoint of achieving lattice matching on the plane perpendicular to the alignment direction at the interface between the solid electrolyte layer 11 and the intermediate layer 12 . In particular, when the material constituting the solid electrolyte layer 11 is represented by the above-mentioned general formula (1), if the material constituting the intermediate layer 12 is a perovskite-type oxide, the above-mentioned lattice matching can always be achieved satisfactorily.

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

_Among the composite oxides represented by the general formula (2), those represented by La _0.6 Sr _0.4 Co _0.9 Ni _0.1 O _{3 -δ} are particularly preferable.

The intermediate layer 12 including the composite oxide represented by the general formula (2) can be formed on one side of the solid electrolyte layer 11 using various thin film forming methods, for example. As a thin film forming method, a physical vapor deposition method, a chemical vapor deposition method, etc. are mentioned, and the intermediate layer 12 can always be formed better by using the physical vapor deposition method among these. Among the physical vapor deposition methods, it is particularly preferable to use a PLD (Pulsed Laser Deposition, pulsed laser deposition) method.

Even if the material constituting the intermediate layer 12 is any of the above-mentioned materials, in terms of reducing the interface resistance, the material constituting the solid electrolyte layer 11 and the material constituting the intermediate layer 12 are all along the solid electrolyte layer 11 and the intermediate layer. The uniaxial alignment in the lamination direction of 12 is more effective. In order to make the material constituting the solid electrolyte layer 11 and the material constituting the intermediate layer 12 uniaxially aligned along the above lamination direction, for example, it is only necessary to heat the solid electrolyte layer 11 as the substrate to a predetermined temperature on one side and control the partial pressure of oxygen on the other hand. Under the circumstances, the thin film of the intermediate layer 12 can be formed on the solid electrolyte layer 11 by physical vapor deposition or chemical vapor deposition, and the thin film of the intermediate layer 12 can be locally epitaxially grown. In addition, atomic layer deposition (ALD, atomic layer deposition) can also be used to form a uniaxially aligned thin film of the intermediate layer 12 on the solid electrolyte layer 11 . However, it is not limited to these methods.

Whether the material constituting the solid electrolyte layer 11 and the material constituting the intermediate layer 12 are uniaxially aligned can be judged by observing the cross-section of the bonding interface using a TEM (transmission electron microscope). 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 shaking.

Even if the material constituting the intermediate layer 12 is any of the above-mentioned materials, the resistance between the intermediate layer 12 and the solid electrolyte layer 11 can be effectively reduced as long as the intermediate layer 12 has a predetermined thickness. Specifically, the thickness of the intermediate layer 12 bonded to the solid electrolyte layer 11 along the lamination direction is preferably 80 nm or more, more preferably 100 nm or more, and more preferably 100 nm or more and 1000 nm or less. The thickness of the middle layer 12 can be measured by a stylus profiler or an electron microscope.

The metal electrode layer 13 formed on the opposite side to the intermediate layer 12 through the solid electrolyte layer 11 is preferably composed of platinum group elements in terms of easy formation and high catalytic activity. Examples of platinum group elements include platinum, ruthenium, rhodium, palladium, osmium, and iridium. These elements may be used alone or in combination of two or more. In addition, a cermet containing a platinum group element can also be used as the metal electrode layer 13 .

The solid electrolyte assembly 10 and the device 20 of the embodiment shown in FIG. 1 can be preferably manufactured by, for example, the method described below. First, solid electrolyte layer 11 is produced by a known method. In production, for example, the method described in JP-A-2013-51101 or US2018/183068A1 can be used.

Next, the intermediate layer 12 is formed on one of the two surfaces of the solid electrolyte layer 11 . In forming the intermediate layer 12, various thin film forming methods can be used. As one of the thin film forming methods, for example, the above-mentioned PLD method can be used. Specifically, in order to uniaxially align 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, the above-mentioned PLD method is used to form When the intermediate layer 12 is formed on one side of the solid electrolyte layer 11, it is only necessary to heat the solid electrolyte layer 11 to a predetermined temperature. The heating temperature is preferably set to, for example, 600° C. or higher and 700° C. or lower from the viewpoint of performing uniaxial alignment better all the time.

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

The target solid electrolyte assembly 10 and device 20 were obtained by the above method. The device 20 obtained in this way is preferably used as various gas sensors represented by oxygen permeable elements, oxygen sensors, water vapor electrolysis or solid electrolyte type fuels by utilizing its higher oxide ion conductivity. battery etc. Regardless of the application for which the device 20 is used, it is advantageous to use the intermediate layer 12 as the cathode, ie as the pole of the reduction reaction that produces oxygen. For example, when the device 20 is used as an oxygen-permeable element, the metal electrode layer 13 is connected to the anode of the DC power supply, and the intermediate layer 12 is connected to the cathode of the DC power supply. Specifies the DC voltage. As a result, oxygen receives electrons on the side of the intermediate layer 12 to generate oxide ions. The generated oxide ions move in the solid electrolyte layer 11 and reach the metal electrode layer 13 . The oxide ions reaching the metal electrode layer 13 release electrons and become oxygen gas. Through this reaction, the solid electrolyte layer 11 allows oxygen contained in the environment on the intermediate layer 12 side to pass through the solid electrolyte layer 11 to the metal electrode layer 13 side. Furthermore, if necessary, a collector 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 oxygen permeation amount. When a voltage is applied between the two electrodes, it is preferable that the oxide ion conductivity of the solid electrolyte layer 11 becomes sufficiently high. For example, the oxide ion conductivity expressed as conductivity is preferably 1.0× ^{10 −3 S} /cm or more. For this purpose, it is preferable to maintain the solid electrolyte layer 11 or the entire device 20 at a predetermined temperature. This holding temperature also depends on the material of the solid electrolyte layer 11, but it is usually preferably set within a range of 300°C to 600°C. By using the device 20 under this condition, oxygen gas contained in the environment on the intermediate layer 12 side can pass 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, a current is generated due to oxide ions generated on the intermediate layer 12 side moving to the metal electrode layer 13 side through the solid electrolyte layer 11 . Since the current value depends on the oxygen concentration on the intermediate layer 12 side, the oxygen concentration on the intermediate layer 12 side can be measured by measuring the current value.

As mentioned above, although this invention was demonstrated based on the preferable embodiment, this invention is not limited to the said embodiment. For example, in the above-mentioned embodiment, the intermediate layer 12 is disposed only on one side of the solid electrolyte layer 11, but it can also be replaced. As shown in FIG. '. When the solid electrolyte layer 11 is provided with another intermediate layer 12 ′ on the surface facing the intermediate layer 12 , the intermediate layers 12 and 12 ′ may be the same or different. In this case, it is preferable that the material constituting the solid electrolyte layer 11, the material constituting the one intermediate layer 12, and the material constituting the other intermediate layer 12' are all uniaxially aligned along the lamination directions.

In addition, instead of forming intermediate layers 12, 12' on each surface of solid electrolyte layer 11, as shown in FIG. 3, metal electrode layers 13, 13' may be formed. In this case, the resistance of the device 20 as a whole can be reduced. The metal electrode layers 13 and 13' may be the same or different. Example

Hereinafter, the present invention will be described in further detail by means of examples. However, the scope of the present invention is not limited to the above-mentioned embodiments. Unless otherwise specified, "%" means "mass %".

[Example 1] La ₂ O ₃ powder and SiO ₂ powder were prepared in a molar ratio of 1:1, ethanol was added and mixed with a ball mill. The mixture was dried, pulverized in a mortar, and baked at 1650° C. for 3 hours in an air atmosphere using a platinum crucible. Ethanol was added to the calcined product, and it was pulverized by a ball mill to obtain a calcined powder. Put the calcined powder into a 20 mm ϕ shaper, and press from one direction for uniaxial molding. Furthermore, cold isostatic pressing (CIP, cold isostatic pressing) was performed at 700 MPa for 1 minute to form pellets. This granular molded body was heated at 1600° C. for 3 hours in the air to obtain a granular sintered body. The sintered body was subjected to powder X-ray diffraction measurement and chemical analysis, and as a result, the structure of La ₂ SiO ₅ having an apatite crystal structure was confirmed.

800 mg of the obtained granules and 140 mg of B ₂ O ₃ powder were put into a sagger with a lid. The particles and B ₂ O ₃ powder were heated in the air at 1550° C. (ambient temperature in the furnace) for 50 hours using an electric furnace. By this heating, B ₂ O ₃ vapor is generated in the sagger, and the B ₂ O ₃ vapor reacts with the particles to obtain the target solid electrolyte layer 11 . In the solid electrolyte layer 11, in La _{9.33 + x} [Si _{6.00 − y} By _y ]O _{26.0 + z} , x=0.50, y=1.17, z=0.16, and the molar ratio of La to Si is 2.04. Also, the thickness measured with a caliper was 350 μm. Hereinafter, this compound is abbreviated as "LSBO".

〔Manufacture of La absorbing film〕 Put the powder of Bi ₂ O ₃ into a 50 mm ϕ shaper, apply pressure from one direction for uniaxial forming, and then perform hot-press sintering. The sintering conditions were set at a nitrogen atmosphere, a pressure of 30 MPa, and a temperature of 600° C. for 3 hours to obtain a target for sputtering. Using this target, sputtering was performed with a thickness of 300 nm on both surfaces of the solid electrolyte layer 11 including LSBO by a high-frequency sputtering method. The conditions of sputtering were that the RF output was 30 W, and the pressure of argon gas was 0.8 Pa. After completion of sputtering, annealing was performed at 750° C. for 1 hour in the air. By this annealing, La in the solid electrolyte diffuses toward the Bi ₂ O ₃ layer (La absorbing layer), forming La-deficient LSBO. Next, an operation of removing the layer having absorbed La from the solid electrolyte is performed. Specifically, the Bi ₂ O ₃ layer having absorbed La was completely removed using a precision polishing device. Thereafter, the thickness of the La-deficient LSBO measured by a caliper was 340 μm.

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

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

[Comparative Example 1] In Example 1, a solid electrolyte was produced in the same manner as in Example 1 except that annealing was not performed because the La absorption layer was not formed.

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

〔XRD measurement〕 The measurement was performed under the following conditions using a fully automatic multi-purpose X-ray diffraction device SmartLab of Rigaku Co., Ltd. Tube voltage: 40 kV Tube current: 30mA X-ray source: CuKα Entrance optics: Confocal mirror (CMF) Incident side slit composition: collimator size 1.4 mm×1.4 mm Light-receiving side slit configuration: Parallel slit analyzer 0.114 deg, light-receiving slit 20 mm Detector: scintillation counter Measuring range: 2θ＝20～60 deg Step width: 0.01 deg Scanning speed: 1 deg/min PDXL2 of Rigaku Co., Ltd. was used for the analysis. The peak intensities (integrated intensities) of 002 and 004 were obtained by contour fitting by selecting a straight line connecting the endpoints for the background and selecting a segmented quasi-Voigt function for the peak shape. The peak of 002 and the peak of 004 are c-axis aligned as described above, so they are independent peaks that do not overlap with peaks of other planes. When it is assumed that peaks from other phases overlap with other phases in the case of a multi-layer structure as a device, only the peak intensities of 002 and 004 can be obtained because the peaks can be decomposed in the same way as in general XRD data analysis.

〔Measurement of conductivity of oxide ions〕 Platinum films with a thickness of 150 nm were formed on both sides of the solid electrolyte by sputtering to form electrodes. This solid electrolyte was placed in a heating furnace, and the temperature of the heating furnace was changed to perform complex impedance analysis of the solid electrolyte. An impedance measurement device was used in the analysis, and the frequency was set at 0.1 Hz to 32 MHz. Calculate the oxide ion conductivity (S/cm) from the total resistance component (intragranular resistance + grain boundary resistance). Table 1 shows the oxide ion conductivity at 600°C.

[Table 1]

It is clear from the results shown in Table 1 that, compared with the solid electrolyte of the comparative example, the conductivity of the solid electrolyte obtained in each example in which the value of I ₀₀₂ /I ₀₀₄ is within a specific range is about 5 times higher, The effect of improving the ion conductivity of oxides is high.

[Example 4] The intermediate layer 12 made of Bi ₂ O ₃ containing yttrium was formed on both surfaces of the solid electrolyte obtained in Example 1. In formation of the intermediate layer 12, the target manufactured by the following method was used. Using this target, sputtering was performed on both surfaces of the solid electrolyte to form an intermediate layer. After the intermediate layer was formed, it was heated at 700° C. for 1 hour to manufacture the solid electrolyte assembly 10 .

[Manufacture of target] Prepare predetermined amounts of Y ₂ O ₃ powder and Bi ₂ O ₃ powder, add ethanol, and mix with a ball mill. This mixture was dried and pulverized in a mortar, and fired at 700° C. for 3 hours in an air atmosphere using an alumina crucible. Ethanol was added to the calcined product, and it was pulverized by a planetary ball mill to obtain a calcined powder. Put the calcined powder into a 50 mm ϕ shaper, press from one direction for uniaxial molding, and then perform hot-press sintering. The sintering conditions were set as a nitrogen 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] Instead of the target used in Example 4, a target comprising samarium-containing cerium oxide was used. This target was produced in the same manner as the target used in Example 4. Using this target, by the same method as in Example 4, the intermediate layer 12 containing samarium-containing cerium oxide was produced. In this way, the solid electrolyte assembly 10 was produced.

[Comparative Example 2] On both sides of the solid electrolyte obtained in Comparative Example 1, an intermediate layer comprising samarium-containing cerium oxide was formed. The formation of the intermediate layer is the same 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. The measurement is carried out 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.

[Table 2]

From the results shown in Table 2, it can be clearly seen that the solid electrolyte assembly provided with the intermediate layer in the value of I ₀₀₂ /I ₀₀₄ within a specific range, compared with the solid electrolyte assembly of the comparative example, can obtain about 7 times the high current density value. [Industrial availability]

According to the present invention, a solid electrolyte capable of reducing the resistance of a device including the solid electrolyte is provided. Also, according to the present invention, a solid electrolyte assembly having low electrical resistance is provided.

10‧‧‧Solid electrolyte junction 11‧‧‧Solid electrolyte layer 12‧‧‧intermediate layer 12'‧‧‧Middle layer 13‧‧‧Metal electrode layer 13'‧‧‧Metal electrode layer 20‧‧‧Devices

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

10‧‧‧Solid electrolyte junction

11‧‧‧Solid electrolyte layer

12‧‧‧intermediate layer

13‧‧‧Metal electrode layer

20‧‧‧Devices

Claims (9)

A solid electrolyte comprising 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 is I The value of ₀₀₂ /I ₀₀₄ is not less than 0.3 and not more than 0.8. The above-mentioned composite oxide has a general formula: A _9.33+x [T _6.00-y M _y ]O _26.0+z (the A in the formula is selected from La, Ce, Pr, One or two or more elements in the group consisting of Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr and Ba, where T contains Si or Ge or elements of both, M in the formula is selected from Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Ge, Zn, One or two or more elements in the group consisting of Sn, W and Mo) means that x in the formula is a number from -1.33 to 1.50, y in the formula is a number from 0.40 to 2.00, and z in the formula is -A number between 5.00 and 5.20, and the ratio of the molar number of A to the molar number of T is 1.33 to 3.61. The solid electrolyte according to claim 1, which is aligned on the c-axis. A solid electrolyte assembly, which is formed by bonding the solid electrolyte according to claim 1 or 2 with an intermediate layer of metal oxide or a metal electrode layer. The solid electrolyte assembly according to claim 3, wherein the metal oxide includes cerium oxide containing one or two or more elements selected from the group consisting of samarium, yttrium, gadolinium, and lanthanum. The solid electrolyte assembly according to claim 3, wherein the metal oxide contains bismuth oxide. The solid electrolyte assembly according to claim 3, wherein the metal oxide includes a mixed conductor having oxide ion conductivity and electron conductivity. The solid electrolyte assembly according to any one of claims 3 to 6, wherein, on the surface of the solid electrolyte assembly opposite to the surface on which the intermediate layer or the electrode layer is arranged, the intermediate layer or the electrode layer is arranged on the solid electrolyte assembly. An intermediate or electrode layer with the same or different electrode layers. The solid electrolyte assembly according to any one of claims 3 to 6, which is used as an oxygen permeable element, a gas sensor, water vapor electrolysis, or a solid electrolyte fuel cell. The solid electrolyte assembly according to claim 7, which is used as an oxygen permeable element, a gas sensor, water vapor electrolysis or a solid electrolyte fuel cell.