Oxide and solid electrolyte assembly containing same

Abstract

This oxide has a perovskite crystal structure. The oxide is represented by the formula A a BbC1cDdO3-δ. A represents a group 3 element. B represents a group 2 element. C represents an element selected from among group 8 elements and group 9 elements. D represents an element selected from among a platinum group element and gold. a represents a number of 0.10-1.10. b represents a number of 0-0.90. c represents a number of 0.40-1.10. d represents a number of 0.15-0.40. The value of a+b is 0.80-1.20. The value of c+d is 0.80-1.20.

Description

Oxide and solid electrolyte joint having the same

[0001] The present invention relates to an oxide and a solid electrolyte joint having the oxide.

[0002] In recent years, fuel cells have been actively developed to popularize clean energy toward the realization of a sustainable society, and various sensors are being developed to ensure health and welfare for all. In this context, oxygen sensors and solid oxide fuel cells are increasingly required to operate at low temperatures and achieve even higher performance in terms of power consumption. When oxides that conduct both electrons and oxide ions are used as electrodes in such devices, dissociation of oxygen molecules can occur on the electrode surface, significantly increasing the reaction field compared to platinum metal electrodes. Therefore, such oxides are expected to be materials that can realize low-temperature operation and high performance in devices.

[0003] For example, Patent Document 1 discloses LaMn ０．９ Pt ０．１ O ３ It has been described that an oxide in which an element in a perovskite oxide is substituted with a noble metal is used as a gas diffusion electrode of an air battery.

[0004] In Non-Patent Document 1, La, a perovskite oxide used in electrodes of intermediate-temperature solid oxide fuel cells, ０．６ Sr ０．４ FeO ３－δ It has been proposed to substitute a portion of the iron at the B site in the ZnSe alloy with platinum or ruthenium.

[0005] JP 2014-049304 A

[0006] ACS Applied Energy Materials 2022, 5, 2918-2928

[0007] Although perovskite oxides conventionally used as electrodes for solid oxide fuel cells have superior electrode activity to platinum, their activity at temperatures below 600°C is insufficient. Furthermore, the oxides described in Patent Document 1 and Non-Patent Document 1 exhibit relatively higher oxide ion conductivity than other oxides, but the resistance attributable to these oxides accounts for a large proportion of the overall device resistance, and their oxide ion conductivity and electronic conductivity are insufficient. Therefore, an object of the present invention is to provide an oxide that has excellent electrode activity due to improved oxide ion conductivity and improved electronic conductivity at relatively low temperatures below 600°C.

[0008] The present invention relates to a compound of formula: A ａ B ｂ C ｃ D ｄ O ３－δ (wherein A represents a Group 3 element, B represents a Group 2 element, C represents an element selected from Group 8 and Group 9 elements, D represents an element selected from platinum group elements and gold, a represents a number of 0.10 or more and 1.10 or less, b represents a number of 0 or more and 0.90 or less, c represents a number of 0.40 or more and 1.10 or less, d represents a number of 0.15 or more and 0.40 or less, a + b is 0.80 or more and 1.20 or less, c + d is 0.80 or more and 1.20 or less, and δ is a fraction resulting from the valences and amounts of A, B, C, D, and O.)

[0009] The present invention further provides a solid electrolyte joined body comprising a layer made of the oxide and a layer of a solid electrolyte joined together.

[0010] FIG. 1 is a schematic diagram of a cross section along the thickness direction showing one embodiment of a device equipped with an electrode made of an oxide of the present invention.

[0011] The present invention will be described below based on its preferred embodiments. The oxide of the present invention has a perovskite crystal structure. The oxide of the present invention preferably has oxide ion conductivity. Oxides having a perovskite crystal structure are generally represented by the formula M Ｉ MII O ３ (hereinafter also referred to as "formula (1)"). The oxide of the present invention has a composition represented by formula (1), Ｉ It is preferable that the site is at least one element selected from Group 3 elements and Group 2 elements from the viewpoint of enhancing oxide ion conductivity and electronic conductivity at low temperatures. II It is preferable that the M site contains at least one element selected from the group consisting of elements of Group 8 and elements of Group 9. II The sites preferably further contain at least one element selected from the platinum group elements and gold, which also increases the oxide ion conductivity and electronic conductivity at low temperatures.

[0012] In the composition formula represented by formula (1), M Ｉ Examples of Group 3 elements located at the ZnO site include lanthanoid elements, actinoid elements, scandium, and yttrium. These elements may be used alone or in combination of two or more. Among these elements, lanthanoid elements, scandium, and yttrium are preferred from the viewpoint of improving oxide ion conductivity and electronic conductivity at low temperatures. Examples of lanthanoid elements include lanthanum, cerium, praseodymium, neodymium, promethium, and samarium. In particular, the use of lanthanum, praseodymium, neodymium, and samarium as Group 3 elements is preferred from the viewpoint of further improving oxide ion conductivity and electronic conductivity at low temperatures.

[0013] M ＩExamples of Group 2 elements located at the Λ site include beryllium, magnesium, calcium, strontium, barium, and radium. These elements may be used alone or in combination of two or more. In particular, using strontium, barium, and calcium as Group 2 elements is preferred from the viewpoint of further enhancing oxide ion conductivity and electronic conductivity at low temperatures. To further enhance this advantage, it is preferred to use strontium or barium as the Group 2 element.

[0014] M Ｉ The elements located at the sites may be only Group 3 elements, only Group 2 elements, or both Group 3 and Group 2 elements. Ｉ The elements located at the sites are preferably at least one Group 3 element and at least one Group 2 element. Ｉ When the elements located at the sites are lanthanum, a Group 3 element, and barium, a Group 2 element, this is preferred because the lattice constant of the oxide of the present invention is large. A large lattice constant of the oxide of the present invention is advantageous in that it improves the diffusion of oxide ions. Ｉ Whether or not a Group 3 element and / or a Group 2 element is located in a part of the site can be confirmed by X-ray diffraction.

[0015] In the composition formula represented by formula (1), M II Examples of Group 8 elements located at the Χ site include iron, ruthenium, and osmium. These elements may be used alone or in combination of two or more. Among these elements, iron and ruthenium are preferred from the viewpoint of increasing oxide ion conductivity and electron conductivity at low temperatures.

[0016] M IIExamples of Group 9 elements located at the ZnO site include cobalt, rhodium, and iridium. These elements may be used alone or in combination of two or more. Among these elements, cobalt is preferred from the viewpoint of increasing oxide ion conductivity and electron conductivity at low temperatures.

[0017] M II The elements located at the sites may be only Group 8 elements, only Group 9 elements, or both Group 8 and Group 9 elements. II The elements located at the sites are preferably at least one Group 8 element and at least one Group 9 element. II Whether or not a Group 8 element and / or a Group 9 element is located in some of the sites can be confirmed by ICP optical emission spectroscopy, energy dispersive X-ray spectroscopy (EDS), or electron probe microanalyzer (EPMA).

[0018] M II As described above, it is also preferable that at least one element selected from platinum group elements and gold is located at the M site. This increases the oxide ion conductivity and electron conductivity at low temperatures. The reason for this is that platinum group elements or gold, which have a larger ionic radius than the Group 8 elements and Group 9 elements, are located at the M site. II The inventors believe that this is because the lattice constant of the oxide of the present invention increases by substituting a portion of the Group 8 element and / or Group 9 element located at the site. As described above, an increase in the lattice constant of the oxide of the present invention is advantageous in that it improves the diffusion of oxide ions. Examples of platinum group elements include ruthenium, rhodium, palladium, osmium, iridium, and platinum. These elements may be used alone or in combination of two or more. Furthermore, at least one platinum group element may be used in combination with gold. Of the above elements, platinum, palladium, rhodium, and iridium are preferably used from the viewpoint of further enhancing oxide ion conductivity and electronic conductivity at low temperatures.

[0019] M IIWhether or not a platinum group element and / or gold is located in some of the sites can be confirmed by X-ray diffraction, energy dispersive X-ray spectroscopy (EDS), or electron probe microanalyzer (EPMA).

[0020] Formula M Ｉ M II O ３ The oxide of the present invention having a perovskite crystal structure represented by formula (1) is ａ B ｂ C ｃ D ｄ O ３－δ (hereinafter also referred to as "formula (2)"). In the formula, A represents a Group 3 element. B represents a Group 2 element. C represents an element selected from Group 8 elements and Group 9 elements. D represents an element selected from platinum group elements and gold. a represents a number of 0.10 or more and 1.10 or less. b represents a number of 0 or more and 0.90 or less. c represents a number of 0.40 or more and 1.10 or less. d represents a number of 0.15 or more and 0.40 or less. δ is a fraction resulting from the valence and amount of A, B, C, D, and O. a + b is 0.80 or more and 1.20, and c + d is 0.80 or more and 1.20. When the oxide of the present invention has a composition formula represented by formula (2), the oxide has further improved oxide ion conductivity and electronic conductivity at low temperatures.

[0021] In formula (2), the preferred range for a is 0.20 to 1.05, more preferably 0.20 to 0.90, even more preferably 0.40 to 0.85, and even more preferably 0.40 to 0.70, from the viewpoint of further enhancing oxide ion conductivity and electronic conductivity at low temperatures. From the same viewpoint, the preferred range for b in formula (2) is 0.10 to 0.60, even more preferably 0.20 to 0.40. From the same viewpoint, the preferred range for c in formula (2) is 0.50 to 1.00, even more preferably 0.6 to 0.9. From the same viewpoint, the preferred range for d in formula (2) is 0.20 to 0.35, and even more preferably 0.25 to 0.30. From the same viewpoint, the preferable range of a+b in formula (2) is 0.85 or more and 1.15 or less, and the more preferable range is 0.90 or more and 1.10 or less. From the same viewpoint, the preferable range of c+d in formula (2) is 0.85 or more and 1.15 or less, and the more preferable range is 0.90 or more and 1.10 or less.

[0022] In formula (2), the Group 3 element represented by A is preferably lanthanum. The Group 2 element represented by B is preferably strontium or barium. The Group 8 element and / or Group 9 element represented by C is preferably cobalt and iron. The element represented by D is preferably platinum. When the oxide represented by formula (2) is composed of these elements, the oxide ion conductivity and electronic conductivity at low temperatures are further improved.

[0023] In the oxide represented by formula (2), the proportion of each element can be measured by energy dispersive X-ray spectroscopy (EDS), electron probe microanalyzer (EPMA), or ICP optical emission spectroscopy.

[0024] Among the oxides represented by formula (2), the most preferred are those represented by formula La Ｘ１ Sr Ｘ２ Co Ｘ３ Fe Ｘ４ Pt Ｘ５ O ３－δ (hereinafter also referred to as "formula (3)") and formula La Ｘ１ BaＸ２ Co Ｘ３ Fe Ｘ４ Pt Ｘ５ O ３－δ (hereinafter also referred to as "formula (4)"). In formulas (3) and (4), X1 represents a number of 0.10 or more and 1.10 or less, preferably 0.20 or more and 1.05 or less, more preferably 0.20 or more and 0.90 or less, and even more preferably 0.40 or more and 0.70 or less. X2 represents a number of 0.00 or more and 0.90 or less, preferably 0.10 or more and 0.60 or less, and even more preferably 0.20 or more and 0.40 or less. X3 represents a number of 0.05 or more and 1.05 or less, preferably 0.10 or more and 1.00 or less, more preferably 0.20 or more and 0.90 or less, and even more preferably 0.25 or more and 0.60 or less. X4 represents a number of 0.05 or more and 1.05 or less, preferably 0.10 or more and 1.00 or less, more preferably 0.20 or more and 0.90 or less, and even more preferably 0.25 or more and 0.50 or less. X5 represents a number of more than 0.15 and 0.40 or less, preferably 0.16 or more and 0.35 or less, and even more preferably 0.20 or more and 0.35 or less. X3 + X4 is 0.40 or more and 1.10 or less, preferably 0.50 or more and 1.0 or less, more preferably 0.60 or more and 0.90 or less, and even more preferably 0.60 or more and 0.85 or less. X3 / X4 is 0.10 or more and 9.0 or less, preferably 0.15 or more and 5.0 or less, more preferably 0.20 or more and 3.0 or less, even more preferably 0.20 or more and 1.18 or less, and particularly preferably 1.00 or more and 2.00 or less.

[0025] The oxide of the present invention has high oxide ion conductivity and electron conductivity. Specifically, when electrodes are formed on each side of a solid electrolyte and a direct current voltage of 0.5 V is applied between the electrodes, the current density obtained is preferably 170 mA / cm at 600°C in the atmosphere. ２ More preferably, 180 mA / cm ２ More preferably, 185 mA / cm ２ The method for forming electrodes on each surface of the solid electrolyte and the materials for the electrodes will be explained in the examples below.

[0026] The oxide of the present invention may be, for example, a powder. Alternatively, the oxide of the present invention may be a sintered body obtained by molding and firing the powder. When the oxide of the present invention is a powder, the average particle size is preferably 1,000 nm or less, more preferably 600 nm or less, even more preferably 300 nm or less, and even more preferably 200 nm or less, from the viewpoint of enhancing oxide ion conductivity. Furthermore, the average particle size of the oxide is preferably 1 nm or more, even more preferably 2 nm or more, and even more preferably 3 nm or more. The average particle size can be calculated using images of particles obtained by scanning electron microscope observation and known image analysis software. For example, the outlines of 10 randomly selected particles are observed at 1,000 to 100,000 magnifications to determine the particle contours, and the average particle size can be calculated by performing image analysis after processing such as contrast enhancement or drawing lines along the contours as necessary.

[0027] The oxide of the present invention can be obtained by a breakdown method, which uses mechanical energy to reduce particle size, or a build-up method, which controls the growth of atomic or molecular aggregates through chemical reactions. The build-up method is preferable from the perspective of reducing electrical resistance. The build-up method facilitates the production of fine particles and increases the contact area between particles, making it easy to reduce electrical resistance. Specifically, it can be obtained, for example, by the following method. Acetates or nitrates of the metals mixed in a stoichiometric ratio according to the composition of the oxide having the desired perovskite crystal structure and DL-malic acid are dissolved in ion-exchange water, and ammonia water is added while stirring to adjust the pH to approximately 4 to 7. The solution is then evaporated at approximately 350°C, and the resulting powder is pulverized in a mortar. The powder thus obtained is calcined in air at 800 to 1000°C for 2 to 7 hours and then pulverized again. However, this method is not limited to this method.

[0028] Taking advantage of its high oxide ion conductivity, the oxide of the present invention can be used, for example, as an oxide electrode bonded to a solid electrolyte layer. FIG. 1 shows a solid electrolyte bonded assembly formed by bonding a layer made of the oxide of the present invention to a layer of a solid electrolyte. As shown in the figure, the solid electrolyte bonded assembly 10 includes a layer made of a solid electrolyte (hereinafter referred to as a "solid electrolyte layer") 11. The solid electrolyte layer 11 is a solid electrolyte made of an oxide ion conductor and has oxide ion conductivity at a predetermined temperature or higher. A first electrode layer 12 is bonded to one surface of the solid electrolyte layer 11 in contact with the solid electrolyte layer 11. The solid electrolyte layer 11 and the first electrode layer 12 are in direct contact with each other, with no other layer interposed between them. The first electrode layer 12 is made of the oxide of the present invention and has oxide ion conductivity and electron conductivity. The solid electrolyte layer 11 and the first electrode layer 12 constitute the solid electrolyte bonded assembly 10.

[0029] 1 , the second electrode layer 13 may be disposed on one of the two surfaces of the solid electrolyte layer 11 opposite to the surface on which the first electrode layer 12 is disposed. The device 20 is configured by disposing the solid electrolyte layer 11, the first electrode layer 12, and the second electrode layer 13 in this order. The solid electrolyte layer 11 and the second electrode layer 13 are in direct contact with each other, with no other layer interposed between them.

[0030] 1, the solid electrolyte layer 11 and the first electrode layer 12 are shown to have different sizes, but the size relationship between the two is not limited to this, and for example, the solid electrolyte layer 11 and the first electrode layer 12 may be the same size. The same applies to the solid electrolyte layer 11 and the second electrode layer 13, and they may be the same size, or, for example, the solid electrolyte layer 11 may be larger than the second electrode layer 13.

[0031] The solid electrolyte layer 11 is a conductor in which oxide ions serve as carriers. A single-crystal or polycrystalline material is used as the solid electrolyte constituting the solid electrolyte layer 11. In particular, it is preferable to use lanthanum oxide as the material constituting the solid electrolyte layer 11, since this further increases the oxide ion conductivity. Examples of lanthanum oxide include composite oxides containing lanthanum and gallium, composite oxides in which strontium, magnesium, cobalt, or the like is added to such composite oxides, and composite oxides containing lanthanum and molybdenum. In particular, it is preferable to use an oxide ion conductive material made of a composite oxide of lanthanum and silicon, because of its high oxide ion conductivity.

[0032] The composite oxide of lanthanum and silicon includes, for example, an apatite-type composite oxide containing lanthanum and silicon. The apatite-type composite oxide contains lanthanum, which is a trivalent element, silicon, which is a tetravalent element, and O, and has a composition of La. ｘ Si ６ O １．５ｘ＋１２ (X represents a number of 8 or more and 10 or less) is preferred from the viewpoint of high oxide ion conductivity. When this apatite-type complex oxide is used as the solid electrolyte layer 11, it is preferred to form each layer so that the c-axis of the material constituting the solid electrolyte and the c-axis of the oxide constituting the first electrode layer 12 are oriented along the stacking direction of the solid electrolyte layer 11 and the first electrode layer 12. The most preferred composition of this apatite-type complex 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.

[0033] Another example of the material for forming the solid electrolyte layer 11 is a material having the general formula: E ９．３３＋ｘ [T ６．００－ｙ M ｙ ]O ２６．０＋ｚExamples of the composite oxide include those represented by the formula: This composite oxide also has an apatite structure. In the formula, E is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba. In the formula, T is an element containing Si or Ge, or both. In the formula, M is one or more elements selected from the group consisting of B, Ge, Zn, Sn, W, and Mo. From the viewpoint of improving the c-axis orientation, M is preferably one or more elements selected from the group consisting of B, Ge, and Zn.

[0034] In the formula, x is preferably -1.00 or more and 1.00 or less, more preferably 0.00 or more and 0.70 or less, and even more preferably 0.45 or more and 0.65 or less, from the viewpoint of increasing the degree of orientation and oxide ion conductivity. In the formula, y is preferably 0.40 or more and 3.00 or less, more preferably 0.40 or more and 2.00 or less, and even more preferably 0.40 or more and 1.00 or less, from the viewpoint of filling the T element position in the apatite-type crystal lattice. In the formula, z is preferably -3.00 or more and 2.00 or less, more preferably -2.00 or more and 1.50 or less, and even more preferably -1.00 or more and 1.00 or less, from the viewpoint of maintaining electrical neutrality in the apatite-type crystal lattice.

[0035] In the above formula, the ratio of the number of moles of E to the number of moles of M, in other words, (9.33+x) / y in the above formula, is preferably 3.00 or more and 26.0 or less, from the viewpoint of maintaining the spatial occupancy rate in the apatite-type crystal lattice.

[0036] The thickness of the solid electrolyte layer 11 is preferably 10 nm to 1000 μm, more preferably 50 nm to 700 μm, and even more preferably 100 nm to 500 μm, from the viewpoint of effectively reducing the electrical resistance of the solid electrolyte joined body 10. The thickness of the solid electrolyte layer 11 can be measured using, for example, a stylus profilometer or an electron microscope.

[0037] When the first electrode layer 12 has a predetermined thickness, it can further increase the oxide ion conductivity of the entire solid electrolyte joined assembly 10. Specifically, the thickness of the first electrode layer 12 joined to the solid electrolyte layer 11 along the stacking direction is preferably 100 nm or more, more preferably 500 nm or more, and even more preferably 1000 nm or more and 30000 nm or less. The thickness of the first electrode layer 12 can be measured using a stylus profilometer or an electron microscope.

[0038] The second electrode layer 13, which is formed on the opposite side of the solid electrolyte layer 11 from the first electrode layer 12, is composed of, for example, an oxide different from the oxide constituting the first electrode layer 12. Alternatively, the second electrode layer 13 may be a metal electrode. When the second electrode layer 13 is a metal electrode, it is preferable that the second electrode layer 13 be composed of a platinum group element, since such a metal electrode has advantages such as being easier to form and having higher catalytic activity than an oxide. 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. Furthermore, a cermet containing a platinum group element can also be used as the metal electrode. The thickness of the second electrode layer 13 can be within the thickness range of the first electrode layer 12 described above.

[0039] The solid electrolyte assembly 10 and the device 20 of the embodiment shown in Fig. 1 can be suitably manufactured by, for example, the method described below. First, the solid electrolyte layer 11 is manufactured by a known method. For example, the methods described in the above-mentioned JP 2013-51101 A and WO 2016 / 111110 can be adopted for the manufacturing.

[0040] Next, a first electrode layer 12 is formed on one of the two surfaces of the solid electrolyte layer 11. The first electrode layer 12 can be formed, for example, by applying a slurry containing the oxide powder of the present invention to one surface of the solid electrolyte layer 11 to form a coating film, and then firing the coating film. The slurry can be obtained by adding the oxide powder to a binder, for example, ethyl cellulose dissolved in α-terpineol, and adjusting the concentration. The concentration of the oxide powder in the slurry can be, for example, 10% by mass to 40% by mass. The firing conditions for the coating film formed by applying this slurry include, for example, an oxygen-containing atmosphere such as air, or an inert atmosphere such as nitrogen gas or argon gas. The firing temperature is preferably 700°C to 1200°C, more preferably 800°C to 1100°C, and even more preferably 900°C to 1000°C. The firing time is preferably 1 hour to 10 hours, more preferably 3 hours to 8 hours, and even more preferably 5 hours to 7 hours.

[0041] After the formation of the first electrode layer 12, or simultaneously with the formation of the first electrode layer 12, the second electrode layer 13 can be formed on the surface of the solid electrolyte layer 11 opposite to the surface on which the first electrode layer 12 is formed. When the second electrode layer 13 is an oxide of the same type as the oxide forming the first electrode layer 12, the second electrode layer 13 can be formed in the same manner as the first electrode layer 12. When the second electrode layer 13 is a metal electrode, a paste containing particles of a platinum group metal can be used to form the metal electrode. The paste is applied to the surface of the solid electrolyte layer 11 to form a coating film, and the coating film is then fired to form a metal electrode made of a porous body. The firing conditions can be a temperature of 600°C or higher and a time of 30 to 120 minutes. The atmosphere can be an oxygen-containing atmosphere such as air.

[0042] The above method results in the desired solid electrolyte junction 10 and device 20. The device 20 thus obtained is suitable for use as, for example, an oxygen permeation element, a gas sensor, or a solid electrolyte fuel cell, taking advantage of its high oxide ion conductivity. Regardless of the application of the device 20, it is advantageous to use the first electrode layer 12 as a cathode, i.e., as an electrode where a reduction reaction of oxygen gas occurs. For example, when the device 20 is used as an oxygen permeation element, the second electrode layer 13 is connected to the anode of a DC power supply, and the first electrode layer 12 is connected to the cathode of the DC power supply, and a predetermined DC voltage is applied between the first electrode layer 12 and the second electrode layer 13. As a result, oxygen accepts electrons on the first electrode layer 12 side, generating oxide ions. The generated oxide ions migrate through the solid electrolyte layer 11 and reach the second electrode layer 13. Upon reaching the second electrode layer 13, the oxide ions release electrons and become oxygen gas. This reaction allows the solid electrolyte layer 11 to transmit oxygen gas contained in the atmosphere on the first electrode layer 12 side to the second electrode layer 13 side through the solid electrolyte layer 11. If necessary, a current collecting layer made of a conductive material such as platinum may be further formed on at least one of the surfaces of the first electrode layer 12 and the second electrode layer 13.

[0043] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, "%" means "% by mass."

[0044] [Examples 1 to 5 and Comparative Examples 1 to 3] La, an oxide having a cubic perovskite crystal structure, Ｘ１ Sr Ｘ２ Co Ｘ３ Fe Ｘ４ Pt Ｘ５ O ３－δ and La Ｘ１ Ba Ｘ２ Co Ｘ３ Fe Ｘ４ Pt Ｘ５ O ３－δwas synthesized. This oxide was obtained by the following method. First, lanthanum nitrate, strontium nitrate or barium nitrate, cobalt nitrate, iron nitrate, and tetraammineplatinum(II) nitrate were weighed out to obtain the composition shown in Table 1 below. These were dissolved in ion-exchanged water along with DL-malic acid, and ammonia water was added while stirring to adjust the pH to approximately 5.0 to 6.0. The solution was then evaporated at approximately 350°C to obtain a powder (build-up method). The obtained powder was pulverized in a mortar. The powder thus obtained was pre-calcined in air at 900°C for 5 hours to produce the desired oxide powder. X-ray diffraction peaks confirmed that this oxide was a single phase having a perovskite-type crystal structure.

[0045] [Evaluation] Solid electrolyte assemblies were produced using the oxides obtained in Examples 1 to 3 and Comparative Examples 1 and 2, and the current density of the solid electrolyte assemblies was measured by the following method. The results are shown in Table 1 below. Furthermore, the polarization resistance of the oxides obtained in Examples 2, 4, and 5 and Comparative Example 1 was measured by the following method. The results are shown in Table 2 below.

[0046] [Measurement of current density] The oxide powders obtained in the examples and comparative examples were dispersed in a binder prepared by dissolving ethyl cellulose in α-terpineol to prepare a 25% paste. ９．３３＋ｘ [Si ６．００－ｙ B ｙ ]O ２６．０＋ｚ A coating film was formed on each surface of the solid electrolyte assembly (x = 0.50, y = 1.17, z = 0.16). These coating films were fired in an air atmosphere at 900°C for 5 hours to form electrodes made of porous bodies, thereby producing solid electrolyte assemblies. The current density of this solid electrolyte assembly was measured. The measurement was carried out at 600°C. A direct current of 0.5 V was applied between the electrodes of the solid electrolyte assemblies in the air, and the current density was measured.

[0047] [Measurement of polarization resistance] The oxide powders obtained in the examples and comparative examples were dispersed in a binder prepared by dissolving ethyl cellulose in α-terpineol to prepare a 50% paste. ９．３３＋ｘ [Si６．００－ｙ B ｙ ]O ２６．０＋ｚ A coating film was formed by applying the coating film to each surface of the porous body (x = 0.50, y = 1.17, z = 0.16). These coating films were fired in an air atmosphere at 900°C for 5 hours to form electrodes made of porous bodies, thereby producing solid electrolyte assemblies. After holding this solid electrolyte assemblies at 700°C for 30 minutes, the resistance at the same temperature was measured by an AC impedance method. The measurement was performed by applying an AC voltage with an amplitude of 10 mV and a frequency range of 0.1 to 100,000 Hz. The measurement atmosphere was air. The polarization resistance was calculated from the obtained Nyquist Plot.

[0048]

[0049]

[0050] As is clear from the results shown in Table 1, the solid electrolyte assemblies manufactured from the oxides obtained in each Example have a higher current density than the solid electrolyte assemblies of the Comparative Examples at a relatively low temperature of 600° C. As is clear from the results shown in Table 2, the oxides obtained in each Example have a lower polarization resistance than the oxides of the Comparative Examples.

[0051] The oxide of the present invention makes it possible to lower the operating temperature and improve the response speed of devices such as gas sensors that contain the oxide, and also makes it possible to improve the output characteristics of fuel cells that contain the oxide.

Claims

1. Formula: A ａ B ｂ C ｃ D ｄ O ３－δ (In the formula, A represents a Group 3 element, B represents a Group 2 element, C represents an element selected from Group 8 elements and Group 9 elements, D represents an element selected from platinum group elements and gold, a represents a number of 0.10 or more and 1.10 or less, b represents a number of 0 or more and 0.90 or less, c represents a number of 0.40 or more and 1.10 or less, d represents a number of 0.15 or more and 0.40 or less, a + b is 0.80 or more and 1.20 or less, c + d is 0.80 or more and 1.20 or less, and δ is a fraction resulting from the valences and amounts of A, B, C, D, and O.) 2. The oxide according to claim 1, wherein the Group 3 element is La, the Group 2 element is Sr or Ba, the Group 8 element is Co, and the Group 9 element is Fe.

3. A solid electrolyte joint comprising a layer made of the oxide according to claim 1 or 2 joined to a layer of a solid electrolyte.

4. The solid electrolyte joint according to claim 3, wherein the solid electrolyte is an oxide ion conductor.

5. A solid electrolyte joint according to claim 3, wherein the solid electrolyte is an apatite-type composite oxide.

6. The solid electrolyte is represented by the general formula: E ９．３３＋ｘ [T ６．００－ｙ M ｙ ]O ２６．０＋ｚ (E in the formula is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba. T in the formula is an element containing Si or Ge, or both. M in the formula is one or more elements selected from the group consisting of B, Ge, Zn, Sn, W, and Mo), in which x in the formula is a number from −1.00 to 1.00, y in the formula is a number from 0.40 to 3.00, and z in the formula is a number from −3.00 to 2.00, and a ratio of the number of moles of A to the number of moles of M is 3.00 to 26.

0.

7. The current density obtained by applying a direct current voltage of 0.5 V to the solid electrolyte is 170 mA / cm at 600° C. in air. ２ The solid electrolyte joint according to claim 3 .

8. A solid electrolyte joint according to claim 3, wherein a layer of an oxide different from the oxide or a layer of a metal is joined to a surface of the solid electrolyte layer opposite to the surface on which the oxide layer is arranged.

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