JPH11335164A - Oxide ion conductor and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exhibit higher oxide ion conductivity than stabilized zirconia, high heat resistance, high ion conductivity even at low temperatures, small dependence of ion conductivity on oxygen partial pressure, and ion conduction. Provided is an oxide ion conductor which is useful for an electrolyte or an air electrode of a solid oxide fuel cell, an oxygen sensor, and the like, and which can be used also for an oxygen separation membrane, in which a ratio of conductivity and electron conductivity can be freely controlled. SOLUTION: General formula: Ln _1-x A _x Ga _1-yz B1 _y B2 _z O
An oxide ion conductor represented by ₃ (where Ln = La, Ce,
Pr, Nd, Sm; A = Sr, Ca, Ba; B1 = Mg, Al, In; B2 = C
o, Fe, Ni, Cu; x = 0.05-0.3; y = 0-0.29; z =
0.01-0.3; y + z = 0.025-0.3).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth gallate-based oxide ion conductor having a perovskite structure. The oxide ion conductor of the present invention exhibits very high oxide ion conductivity or mixed oxide ion conductivity without being greatly affected by the oxygen partial pressure, and is used for fuel cell electrolytes or air electrodes, gas for oxygen sensors and the like. It is useful as a sensor, an oxygen separation membrane for an electrochemical oxygen pump, a gas separation membrane, and the like.

[0002]

2. Description of the Related Art An oxide ion conductor having a low electronic electric conductivity and exhibiting an electric conductivity mainly by movement of an oxide ion (O ²⁻ ) generally contains other metal to generate O ²⁻ vacancies. It has been attempted to be applied to solid oxide type (solid electrolyte type) fuel cell (SOFC) electrolytes, gas sensors such as oxygen sensors, oxygen separation membranes for electrochemical oxygen pumps, etc., which consist of doped metal oxides.

A typical example of an oxide ion conductor is a solid solution of zirconium oxide (ZrO ₂ ) with a small amount of a divalent or trivalent metal oxide such as CaO, MgO, Y ₂ O ₃ and Gd ₂ O ₃ . Cubic fluorite-type solid solution called stabilized zirconia. Stabilized zirconia has excellent heat resistance, and oxide ion conductivity is dominant under all oxygen partial pressures from an oxygen atmosphere to a hydrogen atmosphere. (Ratio of oxide ion conductivity to electrical conductivity)
Is not easily reduced.

[0004] Therefore, stabilized zirconia is widely used as a zirconia (oxygen) sensor for controlling various industrial processes such as steelmaking and for controlling combustion (air-fuel ratio) of an automobile engine. 1000 ℃ under development
It is also used as an electrolyte in solid oxide fuel cells (SOFCs) that operate before and after. However, the oxide ion conductivity of the stabilized zirconia is not sufficiently high, and the conductivity becomes insufficient particularly at low temperatures. For example, the ionic conductivity of Y ₂ O ₃ stabilized zirconia is 10 ⁻¹ S / cm at 1000 ° C., but drops to 10 ⁻⁴ S / cm at 500 ° C., so that the operating temperature is at least 800 ° C. Is limited to high temperatures.

As a fluorite-type oxide exhibiting extremely high oxide ion conductivity over stabilized zirconia, Bi ₂ O ₃
There is a Bi ₂ O ₃ -based oxide in which Y ₂ O ₃ is dissolved. This oxide has very high oxide ion conductivity, but has a melting temperature of 85.
Since the temperature is as low as 0 ° C or less, the heat resistance is insufficient. Moreover,
It is weak to reducing atmosphere, and when the oxygen partial pressure drops, Bi ³⁺ → Bi ²⁺ changes to show n-type electronic electrical conduction, and when the oxygen partial pressure drops and it approaches a pure hydrogen atmosphere, it is reduced to metal. Therefore, it cannot be used for a solid oxide fuel cell.

[0006] Among other fluorite-type oxide ion conductors, ThO ₂ -based oxides have much lower oxide ion conductivity than stabilized zirconia, and electronic conductivity becomes dominant at low oxygen partial pressure. Therefore, the ion transport number is significantly reduced.
Although CeO ₂ -based oxides exhibit oxide ion conductivity superior to stabilized zirconia, when the oxygen partial pressure falls below 10 ^-12 atm, the change in Ce ⁴⁺ → Ce ³⁺ leads to n-type electronic conduction. Appears again, the ion transport number drops significantly.

PbWO ₄ , LaAlO ₃ , and CaTiO ₃ are known as oxide ion conductors having a crystal structure other than the fluorite type, all of which have low oxide ion conductivity and low oxygen content. Under pressure, semiconductivity appears and electronic conduction becomes dominant, lowering the ion transport number.

[0008]

SUMMARY OF THE INVENTION As explained above,
Oxide ion conductors with higher oxide ion conductivity than stabilized zirconia are known, but their heat resistance is insufficient, and electronic conductivity becomes dominant at low oxygen partial pressures, and the ion transport number increases. Because of the drastic reduction, it was not suitable for applications such as electrolytes of solid oxide fuel cells and oxygen sensors.

The present invention is intended to exhibit higher oxide ion conductivity than stabilized zirconia, high heat resistance, high oxide ion conductivity at high temperatures as well as at low temperatures, and more preferably from an oxygen atmosphere to hydrogen. Oxide ionic conductors that exhibit low ion transport numbers at any oxygen partial pressure up to the atmosphere (that is, low oxygen partial pressure) and dominant in oxide ion conduction, or exhibit mixed ion conductivity The task is to provide

[0010]

Means for Solving the Problems The inventors of the present invention have studied ABO ₃ having a perovskite structure (where A represents one or more lanthanoid-based rare earth elements) while conducting research for the purpose of solving the above problems. In the rare earth gallate-based oxide represented by Ga), part of the rare earth metal at the A site is an alkaline earth metal and / or part of the Ga atom at the B site is a non-metal such as Mg, In, or Al. It has been found that substitution with a transition metal results in a material having high oxide ion conductivity. Among them, the material represented by La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ showed high oxide ion conductivity.

FIG. 1 shows a graph comparing the electric conductivity of this compound with that of a conventional oxide ion conductor. As can be seen from this graph, La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ has much higher conductivity than Y ₂ O ₃ stabilized zirconia and CaO stabilized zirconia, which are typical conventional stabilized zirconia.
(Electric conductivity, the same applies hereinafter). Bi ₂ O ₃ -based oxides show higher conductivity than this, but as described above, they have insufficient heat resistance and are weak in reducing atmospheres, so practical application as oxide ion conductors is difficult. .

The present inventors have further investigated materials having higher oxide ion conductivity. As a result, when a small amount of a specific transition metal is contained in the B site of the rare earth gallate-based oxide, the oxide ion conductivity becomes higher. The present inventors have further found that they exhibit higher oxide ion conductivity even at low temperatures, and have reached the present invention.

Here, the present invention is an oxide ion conductor represented by the following general formula. Ln _1-x A _x Ga _1-yz B1 _y B2 _z O ₃ ... wherein, in the formula, one or more of Ln = La, Ce, Pr, Nd, and Sm; A = 1 of Sr, Ca, and Ba Species or two or more species; B1 = Mg,
One or two or more of Al and In; B2 = one or two or more of Co, Fe, Ni, and Cu; x = 0.05 to 0.3; y = 0 to 0.2
9; z = 0.01-0.3; y + z = 0.025-0.3.

In the present invention, "oxide ion conductor"
Means an electrically conductive material that exhibits substantial oxide ion conductivity. That is, not only the oxide ion conductor in the narrow sense where the oxide ion conductivity occupies most of the electric conductivity, but also the electron conductivity sometimes called an electron-ion mixed conductor (or oxide ion mixed conductor). In the present invention, a material having a large ratio of both oxide ion conductivity and oxide ion conductivity is also included in the oxide ion conductor as a material exhibiting oxide ion conductivity.

In the case of an oxide ion conductor in a narrow sense, where the oxide ion conductivity occupies most of the electric conductivity, the ion transport number
(Ratio of oxide ion conductivity to electric conductivity) is preferably 0.7 or more, and more preferably 0.9 or more. On the other hand, in the case of an electron-ion mixed conductor, the ion transport number is preferably 0.1 to 0.7, more preferably 0.2 to 0.
6

According to the present invention, there is also provided a solid oxide fuel cell using the above-mentioned oxide ion conductor for an electrolyte or an air electrode, a gas sensor comprising the oxide ion conductor, an oxygen for an electrochemical oxygen pump. Separation membranes as well as gas separation membranes utilizing gas concentration differences are also provided.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The oxide ion conductor of the present invention represented by the above formula has a perovskite type crystal structure,
The A site of the perovskite crystal represented by ABO ₃ is occupied by the Ln atom and the A atom of the above general formula, and the B site is occupied by the remaining Ga, B1 and B2 atoms. Note that the B1 atom may not be present.

A part of both the A and B sites occupied by a trivalent metal is originally a divalent metal (for example, the above A atom occupying the A site, Mg of B1 occupying the B site) or a transition metal (B2 occupying the B site). Atoms) occupy oxygen vacancies, which cause oxide ion conductivity.
Therefore, the number of oxygen atoms decreases by the amount of the oxygen vacancies.

That is, in the formula, the number of oxygen atoms is indicated as three, but the number of oxygen atoms is actually three or less. However, the number of oxygen vacancies varies not only with the type of the added atoms (A, B1, B2) but also with the temperature, oxygen partial pressure, and the type and amount of B2 atoms, so it is difficult to accurately display the number. . Therefore, in the chemical formula indicating the perovskite-type material in this specification, the value of the oxygen atom ratio is indicated as 3 for convenience.

In the above formula, Ln is a lanthanoid rare earth metal, A is an alkaline earth metal, B1 is a non-transition metal, and B2 is a transition metal. That is, the oxide ion conductor of the present invention is a lanthanoid gallate (LnGa
O ₃ ) as a basic structure, which contains an alkaline earth metal (A),
Three types of non-transition metal (B1) and transition metal (B2), or two types of alkaline earth metal (A) and transition metal (B2)
Five-element system (Ln + A + Ga + B1 + B)
2) Or a quaternary (Ln + A + Ga + B2) composite oxide. Hereinafter, this composite oxide may be referred to as a 5/4 ternary composite oxide.

The quaternary composite oxide of Ln + A + Ga + B1 (the representative example is La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) also shows higher oxide ion conductivity than stabilized zirconia, as shown in FIG. It is an excellent oxide ion conductor. This is referred to as a control quaternary composite oxide in the present invention. According to the present invention,
By substituting a part or all of the B1 atom of the control quaternary composite oxide with a transition metal (B2 atom), an oxide ion generally having higher oxide ion conductivity than the control quaternary composite oxide is obtained. A conductor is obtained.

FIG. 2 shows a control 4 of La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ .
The oxide ion conductor of the present invention in which a part of Mg of the ternary composite oxide is replaced with a transition metal (indicated by M in the general formula of FIG. 2) to form a ternary system (Ln is La, A is Sr , B1 is Mg, B2 is M atom)
Shows the electrical conductivity of

As can be seen from the figure, when the B2 atom (M in the general formula of FIG. 2) is Co or Fe, it exhibits much higher electrical conductivity than the control quaternary composite oxide at any temperature.
In particular, in the control quaternary composite oxide, the low temperature side (the value on the horizontal axis is
(At about 630 ° C. or less), the conductivity is greatly reduced, and therefore, the improvement in conductivity due to the inclusion of Co or Fe is large on the low temperature side. When the B2 element (M) is Ni, the horizontal axis is about 0.9 or more
(At a temperature of about 840 ° C. or lower), the conductivity exceeds the conductivity of the control quaternary composite oxide. When the B2 atom is Cu, the conductivity exceeds that of the control quaternary composite oxide when the abscissa is about 1.1 or more (temperature is about 630 ° C or less). Since the conductivity does not decrease even when the temperature decreases and is almost constant, the horizontal axis is 1.3 or more.
(Temperature below about 500 ° C) shows the highest conductivity in the figure.

Therefore, when the B2 atom is Ni or Cu, it is preferable to use it as an oxide ion conductor at a relatively low temperature. However, as shown in FIG. 1, the control quaternary composite oxide (La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) which was compared in FIG. 2 was stabilized even at the high temperature side where the horizontal axis exceeded 1.0. Since it has much higher conductivity than zirconia, B2 atoms
Even in the case of Cu, the conductivity is sufficiently high not only at the low temperature side but also at the high temperature side as compared with stabilized zirconia.

On the other hand, when the transition metal of the B2 atom is Mn, the conductivity is lower than that of the control quaternary composite oxide on the high-temperature side where the abscissa is 1.1 or less, and the control is low even on the low-temperature side where the abscissa is 1.1 or more. 4
The conductivity is similar to that of the base composite oxide, and the improvement of conductivity by substituting a part of Mg with a transition metal cannot be substantially obtained at any temperature. Therefore, as the B2 atom of the transition metal, one or more selected from Co, Fe, Ni, and Cu can be obtained at least at a part of the temperature in which the conductivity is improved compared to the control quaternary composite oxide. And

If the doping atom at each site, that is, the atomic ratio (x) of the A atom at the A site or the total atomic ratio (y + z) of the B1 atom + B2 atom at the B site is out of the above range, the value of 5 of the present invention is obtained. The electrical conductivity or ionic transport number of the quaternary composite oxide decreases.

FIG. 3 shows the conductivity when the ratio of A atoms (Sr) is changed. The atomic ratio (x) of A atoms is 0.05-0.
3 (= Ln atom ratio is 0.7 ~ 0.95)
It can be seen that the conductivity is reduced.

FIG. 4A shows the total atomic ratio of B1 atom + B2 atom.
It shows the conductivity when (y + z, y: z = 11.5: 8.5) is changed. The conductivity increases as this sum increases. However, as shown in FIG. 4 (b), when the value of y + z increases, the ion transport number decreases. When the value exceeds 0.3 (= atomic ratio of Ga is 0.7), the ion transport number falls below 0.7.

As for the B2 atom among the two types of doped atoms at the B site, as shown in FIG. 5, the electrical conductivity increases as the z value, which is the atomic ratio of the B2 atom (Co), increases. This is because the B2 atom is a transition metal and n
This is because the type or p-type electronic conductivity is easily developed, and as the number of atoms increases, the electronic conductivity increases and the electrical conductivity increases. Accordingly, the ratio of oxide ion conductivity (ion transport number) decreases.

As can be seen from FIG. 5, in the case of a quinary composite oxide having a z value of 0.15 or less, the ion transport number becomes 0.7 or more, and particularly when the z value is 0.10 or less, the ion transport number becomes 0.9 or more. It functions as an oxide ion conductor in a narrow sense as described above. However, in this case, the non-transition metal B1
Without a certain amount of atoms, the contribution of electronic conduction cannot be kept below 0.3. Such a material is used as an electrolyte for a solid oxide fuel cell,
It is useful as a gas sensor, an oxygen separation membrane for an electrochemical oxygen pump, and the like.

On the other hand, when the z value exceeds 0.15, the ion transport number drops to 0.7 or less, and the compound functions as an electron-ion mixed conductor. As described above, such a material is included in the oxide ion conductor in the present invention. Note that the z value is 0.2 (ie, y value = 0), ie, Mg
Even in a quaternary composite oxide in which (B1 atom) is completely replaced by Co (B2 atom), the ion transport number is only about 0.3, and the mixed electron-ion conductor (i.e., oxide-ion mixed conductor) ), And has the highest conductivity as described above. Such a mixed conductor, as described below,
It is useful for an air electrode or a gas separation membrane of a solid oxide fuel cell.

The preferred composition in the above formula is as follows. Ln = La, Nd or mixtures thereof, especially La, A
= Sr, B1 = Mg, B2 = Co, x = 0.10-0.25, especially 0.17-0.
22, y = 0-0.17, especially 0.09-0.13, y + z = 0.10-0.
25, especially 0.15 to 0.20.

The z value is such that when the oxide functions as an oxide ion conductor in a narrow sense having high oxide ion conductivity (ion transport number is 0.7 or more, preferably 0.9 or more), z =
It is preferably 0.02 to 0.15, particularly preferably 0.07 to 0.10. On the other hand, when it is desired to function as an electron-ion mixed conductor, the z value is 0.15 <z ≦ 0.3, preferably 0.15 <z
≦ 0.25.

In a preferred embodiment of the present invention, Ln = La,
A = Sr, B1 = Mg, B2 = Fe, x = 0.1-0.3, y = 0.025
0.20.29, z = 0.01〜0.15, y + z = 0.035〜0.3. That is, this oxide ion conductor is represented by the following equation.

La _1-x Sr _x Ga _{1 -yz} Mg _y Fe _z O ₃ ... where x = 0.1 to 0.3; y = 0.025 to 0.29; z = 0.01 to
0.15; y + z = 0.035-0.3.

The oxide ion conductor represented by the formula shows high electrical conductivity almost independent of the oxygen partial pressure. This electrical conductivity has a slight P-type semiconductivity under a high oxygen partial pressure, and a wide oxygen partial pressure of 1 to 10 ^-21 atm (that is, an oxygen partial pressure ranging from a reducing atmosphere to an oxidizing atmosphere). )
The oxide ion conductivity is dominant, and the ion transport number of electric conductivity is as high as 0.9 or more. As described above, the oxide ion conductor of the present invention has a high ion transport number regardless of the oxygen partial pressure, and at the same time has a high electric conductivity. It is thought to be due to.

FIG. 6 shows a quaternary composite oxide in which part of Mg of the control quaternary composite oxide represented by La _0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ was substituted with Fe (ie, La _0.8 Sr _0.2 Ga _0.8 Mg _0.2-z Fe _z O ₃ )
Shows the electrical conductivity (950 ° C, oxygen partial pressure = ^10-5 atm).
As can be seen from this figure, when a part of Mg is replaced with Fe, the electric conductivity generally increases as compared with the control quaternary composite oxide of z = 0, and the electric conductivity is in the range of z = 0.01 to 0.05. , And reaches a maximum value near z = 0.03.

FIG. 7A shows that La _0.8 Sr _0.2 Ga _0.8 Mg _0.2-z Fe _z
The temperature change (Arrhenius plot) of the electric conductivity of the quaternary composite oxide represented by the formula represented by O ₃ (z = 0.03, 0.05, 0.1, 0.15) and the quaternary composite oxide of z = 0 is shown. FIG. 7 (b) shows the oxygen partial pressure dependence of the electrical conductivity of the quinary composite oxide having z = 0.03 and the related compound in the formula. As can be seen from this figure, the quinary composite oxide shows high electrical conductivity over a wide range of temperature and oxygen partial pressure, and the electrical conductivity shows almost no oxygen partial pressure dependence.
It can be seen that a high ion transport number of 0.9 or more is shown.

Therefore, the quinary composite oxide is useful as an electrolyte for a solid oxide fuel cell, a gas sensor, an oxygen separation membrane for an electrochemical oxygen pump, and the like. Since the oxide ion conductivity is higher than that of stabilized zirconia and the change due to temperature and oxygen partial pressure is small, a product having better performance than stabilized zirconia may be provided.

The preferred composition in the above formula is as follows. x = 0.15 to 0.25, especially 0.17 to 0.22, y = 0.09 to
0.24, especially 0.10-0.20, z = 0.01-0.05, especially about 0.03,
y + z = 0.10-0.25, especially 0.15-0.22.

The oxide ion conductor of the present invention can be manufactured by molding a mixture obtained by mixing powders of the oxides of the component elements in a predetermined mixing ratio by appropriate means, firing and sintering. it can. As the raw material powder, in addition to the oxide, a precursor (eg, carbonate, carboxylic acid, etc.) that is thermally decomposed during firing to become an oxide can also be used. The firing temperature for sintering is 1200 ° C. or higher, preferably 1300 ° C. or higher, and the firing time is several hours to tens of hours. In order to shorten the firing time, the raw material mixture may be pre-fired at a temperature lower than the sintering temperature. This preliminary firing is performed, for example, at 500 to 1300 ° C. for 1 to 1.
It can be carried out by heating for about 10 hours. The prefired mixture is ground, if necessary, then shaped and finally sintered. Molding is uniaxial compression molding, hydrostatic pressing,
Appropriate powder molding means such as extrusion molding and tape cast molding can be employed. The sintering atmosphere including the pre-sintering is preferably an oxidizing atmosphere such as air or an inert gas atmosphere.

Among the oxide ion conductors of the present invention, those having a quinary system having a y value of 0.025 or more and a z value of 0.15 or less are dominated by the oxide ion conductivity in electrical conductivity.
(That is, the ion transport number is 0.7 or more), and the oxide ion conductor in the narrow sense described above is obtained. This material can be used for various oxide ion conductor applications where stabilized zirconia has been used conventionally (eg, SOFC electrolytes, gas sensors). This type of oxide ion conductor of the present invention has higher oxide ion conductivity than stabilized zirconia and can be operated at a low temperature, so that it is expected to provide a product having better performance than stabilized zirconia. .

Although the field of application of oxide ion conductors such as YSZ is wide-ranging, one of the important applications is the electrolyte in solid oxide (solid electrolyte) fuel cells (SOFC). SOFC has progressed most developed at present, Y ₂ O ₃ thin films of stabilized zirconia (YSZ) as the electrolyte, a perovskite-type material to the air electrode (cathode) is indicating an electrophilic electrical conductivity
(Example: Sr-containing LaMnO ₃ ), and a fuel electrode (anode) using a metal such as Ni or a cermet such as Ni-YSZ. Since the conductivity of YSZ is low at low temperatures and the power generation efficiency can be increased by operating a turbine generator using the heat of exhaust gas at around 1000 ° C, SOFC using YSZ as electrolyte Designed to operate at high temperatures around ℃.

The SOFC has a large voltage drop due to the resistance loss of the electrolyte, and the thinner the film, the higher the output. Therefore, the electrolyte
YSZ is used as a thin film of about 30 to 50 μm. However, the oxide ion conductivity of YSZ is still small, so that it is necessary to heat it to about 1000 ° C. in order to obtain practically sufficient performance. Operating temperature 1000 ℃ with thin film YSZ with thickness of 30μm
Is reported to be about 0.35 W / cm ² . In order to increase the output of the battery or lower the operating temperature, there have been reports of experimental examples using YSZ thin films as thin as several μm to 10 μm, but such thin films are required for electrolytes. The gas impermeability becomes uncertain, which is undesirable in terms of reliability.

The oxide ion conductor in the narrow sense of the present invention composed of a quinary perovskite oxide can have an oxide ion conductivity much higher than that of YSZ.
For example, even when an SOFC is formed using a thick-film electrolyte that can be manufactured by a sintering method with a thickness of 0.5 mm (= 500 μm), a higher output than the YSZ thin film can be obtained. The maximum power density in this case depends on the type and atomic ratio of B2 atoms, but compared to SOFC using YSZ thin film with a thickness of 30 μm,
At an operating temperature of 1000 ° C, it exceeds this, and at an operating temperature of 800 ° C, it is several times larger (eg, three times or more). Or,
When used with a film having a thickness of about 200 μm, an output density equivalent to that exhibited by a YSZ film having a thickness of 30 μm at 1000 ° C. can be obtained at a low temperature of 600 ° C. to 700 ° C.

When the oxide ion conductor of the present invention is used for an electrolyte of a SOFC, the specific material to be used may be selected according to the operating temperature. For example, when performing turbine generation using exhaust gas at the same time as cogeneration,
Since a high operating temperature of around 1000 ° C is required, use of a quinary composite oxide in which the B2 atom is Co or Fe, especially Co, which exhibits high oxide ion conductivity at such a high temperature, is used for the electrolyte. Is preferred. On the other hand, if the operating temperature is about 800 ° C., those having B2 atoms of Ni can also be used, and if the operating temperature is 600 ° C. or lower, those having B2 atoms of Cu can be used.

Even if the operating temperature is as low as 600 to 700 ° C., the power generation efficiency of the SOFC does not decrease so much by simultaneously generating power using steam or other exhaust gas or simultaneously achieving effective use of energy as a heat source. .
When the operating temperature is lowered in this way, a steel material such as stainless steel can be used for the structural material of the SOFC, and the operating temperature is 1000 ° C.
There is also an advantage that material costs are significantly reduced as compared with materials such as Ni-Cr alloys and ceramics before and after. Traditional
With YSZ, it was not possible to construct a SOFC that operates at such low temperatures, but according to the present invention, from such a low-temperature operation type to a high-temperature operation type, a variety of
SOFC can be built.

In particular, the oxide ion conductor composed of the quinary composite oxide represented by the above formula has a wide temperature range exhibiting high oxide ion conductivity, and thus has a relatively low operating temperature of 600 to 700 ° C. to 1000 ° C. It works well as an SOFC electrolyte at any of the high operating temperatures around ℃.
Therefore, when this oxide ion conductor is selected as the electrolyte, various SOFCs from a low-temperature operation type to a high-temperature operation type can be constructed using only this material.

As described above, since the quinary composite oxide of the present invention has a very high oxide ion conductivity as compared with YSZ, the electrolyte is made thicker and manufactured from a sintered body of about 0.5 mm, for example. Therefore, the mechanical strength and life can be greatly improved, and a SOFC having a higher maximum output density than when YSZ is used as the electrolyte can be manufactured.

The electrode of the SOFC using the quinary oxide ion conductor of the present invention as an electrolyte is not particularly limited, and an electrode material used in a conventional SOFC can be used. For example, the air electrode can be composed of Sm _0.5-0.7 Sr _0.3-0.5 CoO ₃ and the fuel electrode can be composed of Ni metal. Taking this cell configuration, especially increases the output at low temperature, obtain a high maximum power density of greater than 800 ° C. even 1.5 W / cm ^2, so further obtained a relatively high power density even 600 ° C., 600 It is expected that a solid oxide fuel cell capable of operating at a low temperature of not more than ℃ or less, which was not possible conventionally, can be manufactured. The fuel electrode may be a cermet such as Ni—CeO ₂ to reduce electrode overvoltage.
Particularly preferred air electrodes and fuel electrodes will be described later.

The largest application of YSZ at present is an oxygen sensor, which is used in a large amount for controlling the air-fuel ratio of an automobile and also for controlling industrial processes such as steel making. This oxygen sensor is called a solid electrolyte oxygen sensor, and measures the acidity concentration based on the principle of an oxygen concentration cell. That is, if there is a difference in oxygen gas partial pressure between both ends of the material made of the oxide ion conductor, oxide ions diffuse inside the material to form an oxygen concentration cell, so that electrodes are attached to both ends to generate electromotive force. By measuring, the oxygen partial pressure can be measured. The solid electrolyte oxygen sensor can also be used as a sensor for oxygen-containing gases such as SO _x and NO _{x in} addition to oxygen gas.

Although the oxygen sensor made of YSZ is relatively inexpensive, the oxide ion conductivity decreases at low temperatures, so that the sensor can be used only at a high temperature of 600 ° C. or more, and its use has been limited. In contrast, the quinary oxide ion conductor of the present invention in which oxide ion conductivity is dominant (y ≧
0.025, z ≦ 0.15, including those represented by the above formula)
Has a higher oxide ion conductivity than YSZ, so it is useful as a gas sensor, especially an oxygen sensor, and because of its high oxide ion conductivity even at low temperatures, it can be used satisfactorily even at 600 ° C. or lower.

The quinary oxide ion conductor of the present invention in which oxide ion conductivity is dominant (y ≧ 0.025, z ≦ 0.1
5, including those represented by the above formulas) can also be used as an oxygen separation membrane for an electrochemical oxygen pump. When a potential difference is applied to both sides of the separation membrane made of the oxide ion conductor, oxide ions move inside and a current flows, and oxygen flows in one direction from one surface to the other surface. This is an oxygen pump. For example, when air is flowed, oxygen-enriched air is obtained from the opposite surface, and is used as an oxygen separation membrane.

Such an oxygen separation membrane is used, for example, in military aircraft and helicopters to produce oxygen-enriched air from surrounding lean air. It is considered that it may be applied as a substitute for medical oxygen cylinders.

The 5/4 quaternary perovskite-type oxide ion conductor (z> 0.15) of the present invention exhibiting mixed electron-ion conductivity (that is, an ion transport number of 0.7 or less) imparts electrons to oxygen. Both the electron conductivity required to function as an ionization catalyst and a current collector, and the oxide ion conductivity sufficient to function as an oxide ion conductor for transferring oxide ions to the electrolyte. Since it is shown, it is suitable for the material of the above-described SOFC air electrode, and it is preferable that at least a part of the air electrode is formed of this material.

In particular, the electrolyte of the SOFC is made of the quinary material of the present invention (y ≧ 0.025, z ≦ 0.15, especially z ≦ 0.10, including those represented by the above formula), a 5/4 material of the present invention (z> 0.15 in the formula) exhibiting mixed electron-ion conductivity at its air electrode.
, Including the case of y = 0), the SOFC electrolyte and cathode are composed of the same material,
SOFC performance is improved.

To explain this point in detail, in the conventional SOFC, the electrolyte and the air electrode are made of different materials [for example, the electrolyte is YSZ and the air electrode is La (Sr) CoO ₃ ]. In this case, when viewed microscopically at the atomic level, a very thin interfacial layer in which the materials of both layers are mixed at the interface between the electrolyte and the air electrode is generated. Decrease. If the electrolyte and air electrode are made of the same material,
The formation of the interface layer is suppressed, and the interface resistance is reduced.

In addition to the problem of interface resistance, when the electrolyte and the air electrode are made of different materials, the thermal expansion coefficients of the two materials are different from each other, so that the thermal stress applied when the temperature is raised or lowered is increased. This problem is also significantly reduced by forming the electrolyte and the cathode from the same material.

The above interface resistance and thermal stress can be controlled by providing one or two or more intermediate layers having an intermediate composition between these two materials between the electrolyte and the air electrode, and gradually increasing the composition from the electrolyte to the air electrode. Can be further suppressed.

The fuel electrode can be composed of various materials conventionally used as described above. Particularly preferable materials for the fuel electrode are (1) Ni and (2) the general formula: Ce _1-m C _m O ₂ (wherein C represents one or more of Sm, Gd, Y and Ca, m = 0.05 to 0.4). The volume ratio of (1) :( 2) is 95: 5.
It is preferably within the range of ~ 20: 80. More preferably, the m value is 0.1 to 0.3, and the volume ratio of (1) :( 2) is 90: 1.
0 to 40:60.

The structure of the SOFC is not particularly limited, and may be a cylindrical type or a flat type. In the case of the flat type, either a stack type or an integral sintered type (monolith type) may be used. In each case, a basic cell structure is a three-layer laminate in which the electrolyte layer is sandwiched between the air electrode and the fuel electrode (the electrolyte layer has one surface in contact with the air electrode layer and the other surface in contact with the fuel electrode layer). The electrolyte layer is gas-impermeable, and each layer of the air electrode and the fuel electrode is porous so that gas can pass through. In the case of a cylindrical type, an interconnector in which fuel gas (eg, hydrogen) and air (or oxygen) are separately supplied to the inside and outside of the cylinder and a large number of cylindrical cells are provided on a part of the outer surface thereof Connected via In the case of a flat plate type, gas is supplied using a generally flat type interconnector provided with a flow path through which fuel gas and air can be separately supplied. The interconnectors are alternately stacked with the above-described flat-plate cells having a three-layered structure to form a multilayer structure.

One of the rate-limiting reactions in the electrode reaction of SOFC is ionization of oxygen at the air electrode represented by the following equation. 1 / 2O ₂ + 2e ⁻ → O ^{2− Since} this reaction occurs at the interface between the air electrode, the electrolyte, and air, the larger the area of this interface, the greater the amount of reaction. For this reason, for example, the above-mentioned three-layer structure has not been formed into a flat plate, but into a corrugated shape.

In a preferred embodiment of the present invention, as shown in FIG. 8, a cell structure in which irregularities are formed on both surfaces of an electrolyte layer, and a material for an air electrode or a fuel electrode is attached to the surface irregularities in the form of particles. Use. In this case, the main body of the electrolyte layer needs to be gas-impermeable, but the irregularities formed on the surfaces of both surfaces may be porous. The material of this uneven part is
The same material as the electrolyte (ie, oxide ion conductor in a narrow sense)
However, the material is preferably a material exhibiting mixed electron-ion conductivity. For example, the concavo-convex portion on the air electrode side can be made of the material (z> 0.15) according to the present invention, which exhibits mixed electron-ion conductivity. In this case, it is preferable that the individual particles adhered to the uneven portion are made of a material in which electronic electric conduction is dominant, such as a conventional air electrode material.

Such a structure can be formed by first baking the mixed ion-electron conductor particles on the surface of the electrolyte layer, then attaching finer electron conductor particles to the surface thereof, and baking. . Alternatively, the same structure can be realized at a fixed ratio by simply adhering a mixture of the ion-electron mixed conductor particles and the electron conductor particles to the surface of the electrolyte layer and baking the mixture.

Conventional air electrode materials are La (Sr) CoO ₃ , La (S
r) Since it is an electronic conductor that has a dominant electronic conductivity (low ion transport number) such as MnO ₃ , even if oxygen in the air is ionized into oxide ions, it passes through the air electrode material Oxygen ions cannot be sent to the electrolyte. Therefore, when this air electrode material is used, the surface unevenness on the air electrode side in FIG. 8 is made of an electrolyte material, and the air electrode material is attached to the surface unevenness in the form of particles. In this case, as shown in FIG. 9A, the ionization of oxygen occurs at the interface between the three phases of the electrolyte layer, the air electrode particles, and the air, that is, at the outer edge (circumference) of the junction surface between the electrolyte layer and the air electrode particles. It only occurs in a one-dimensional area along. As a result, the polarization of the air electrode increases and the output of the SOFC decreases. In addition, since the electrolyte layer needs to be in contact with air in order to take in oxide ions, the air electrode cannot completely cover the electrolyte layer, and the amount of adhesion is also limited. Therefore, the electrical connection to the external terminal, which depends on the electronic conductivity of the cathode, tends to be incomplete. Alternatively, in order to obtain a sufficient electrical connection, a bridging structure that is rich in voids of a conductive material that roughly covers the three-phase interface and connects the air electrode particles is required. Resistance to passage.

On the other hand, since the material of the air electrode of the present invention exhibits mixed ion-electron conductivity, the material itself can ionize oxygen in the air into oxide ions. Therefore, as described above, the surface irregularities on the air electrode side in FIG. 8 are made of the mixed conductive air electrode material, and individual particles adhered to the irregularities are formed by using the conventional electron conductor air electrode material. Can be composed of In this case, as shown in FIG. 9 (b), the ionization of oxygen occurs at a two-dimensional interface between the surface irregularities of the mixed conductive material and the two phases of air, that is, the entire outer surface of the material. , Because the ionization efficiency is dramatically increased and the polarization of the air electrode can be prevented,
SOFC output is improved. Oxide ions generated by ionization flow through the air electrode material due to the oxide ion conductivity of the mixed conductive air electrode material and flow to the electrolyte. In addition, the mixed conductive air electrode material forming the surface irregularities can also conduct electricity electronically, and can conduct electricity to the external terminals. Adhere to the surface of the uneven portion.

[0067] The fuel electrode, as described above, it is preferably made of Ni and ceria-based material _{(Ce 1-m C m O} 2). Also in this case, the ceria-based material as the mixed oxide ion conductor forms the surface irregularities on the fuel electrode side, and the individual particles on the surface are formed from Ni as the electron conductor. With this configuration, as in the case of the above-described air electrode, the transfer of oxide ions to H ₂ is performed in a two-dimensional region, and the efficiency of the H ₂ O generation reaction is also significantly improved.

The oxide ion conductor (z> 0.15) of the present invention exhibiting mixed electron-ion conductivity can also be used as a gas separation membrane utilizing a gas concentration difference. In the case of a gas separation membrane, there is no need to apply an external potential difference to both sides of the membrane, and the difference in oxygen concentration in the gas on both sides of the separation membrane becomes the driving force for separation. Due to this difference in oxygen concentration, oxide ions flow toward the high concentration side or the low concentration side, and electrons flow in the opposite direction to electrically compensate for this flow. Therefore, if there is not a certain degree of electronic conductivity together with the oxide ion conductivity (that is, if it is not a mixed electron-ion conductor), electrons will not flow and will not function.

[0069] The gas separation membrane, oxygen as well, for example, can also be used for the decomposition of water and NO _X. In the case of water, when oxide ions and hydrogen are decomposed on the surface of the separation membrane, a difference in oxide ion concentration occurs on both sides of the membrane, and this becomes a driving force to allow the flow of oxide ions, and hydrogen does not flow. Since it remains, hydrogen can be produced from water. In the case of NO _X, decompose NO _X is harmless, is separated into nitrogen and oxygen.

In addition, the oxide ion conductor of the present invention
It can also be used for electrochemical reactors and oxygen isotope separation membranes.

[0071]

EXAMPLES (Example 1) La ₂ O ₃ , SrCO ₃ , Ga ₂ O ₃ , MgO,
Each powder of a transition metal oxide selected from CoO, Fe ₂ O ₃ , Ni ₂ O ₃ , CuO, and MnO ₂ was subjected to La _0.8 Sr _0.2 Ga _0.8 Mg _0.1 M
_0.1 O ₃ (M is a transition metal) was mixed at a ratio that produced it, mixed well, and then pre-fired at 1000 ° C. for 6 hours. This pre-fired mixture is crushed, and the thickness is 0.5 mm by an isostatic press.
Compression molded into a disk with a diameter of 15 mm
For 6 hours. When the crystal structure of the obtained sintered body was examined by X-ray diffraction, all of the sintered bodies had a perovskite crystal structure.

The electric conductivity of the obtained sintered body was determined by applying a platinum paste as an electrode to a rectangular parallelepiped sample cut from a disk-shaped sintered body, and connecting a platinum wire to the sintered body at 950 to 1200 ° C.
And baking for 10 to 60 minutes, and the resistance was measured by a DC four-terminal method or an AC two-terminal method in an apparatus capable of adjusting to an arbitrary oxygen partial pressure and temperature. Adjustment of the oxygen partial pressure, O ₂
The test was performed using a mixed gas of —N ₂ , CO—CO ₂ , and H ₂ —H ₂ O.

The measurement results are shown in FIG. 2 and FIG. FIG.
Shows the electrical conductivity (Arrhenius plot of conductivity) when the oxygen partial pressure is constant (10 ^-5 atm) and the temperature is changed. FIG. 10 shows the electrical conductivity (conductivity dependence on oxygen partial pressure) when the temperature is constant (950 ° C.) and the oxygen partial pressure is changed. As already described with reference to FIG. 2, the transition metal is Co,
It can be seen that when Fe, Ni or Cu is used, a part of Mg is replaced with a transition metal, thereby significantly improving conductivity at least at a low temperature side.

From FIG. 10, it can be seen from FIG. 10 that when the transition metal is Ni, Cu or Mn, the conductivity fluctuates due to the oxygen partial pressure, but when the transition metal is Co or Fe, the conductivity changes substantially even when the oxygen partial pressure fluctuates. It can be seen that a certain high conductivity is maintained.

FIG. 5 shows the results of measuring the ion transport number of the compound in which the transition metal is Co, together with the electric conductivity. The ion transport number was determined by making the oxygen partial pressures of the atmospheres at both ends of the sample different from each other by a partition, and measuring the electromotive force of this battery. It was obtained from the equation and was obtained as a ratio of the measured value of the electromotive force to the theoretical electromotive force. Transition metal is Co
5, a tendency almost similar to that of FIG.
As the ratio of the transition metal to the metal increased, the electrical conductivity increased and the ionic transport number decreased. However, since the increase in electrical conductivity is a logarithmic increase, it is much greater than the decrease in ion transport number. Therefore, even when the ion transport number is reduced, the absolute value of the oxide ion conductivity is increased.

(Embodiment 2) In the same manner as in Embodiment 1, La
_An oxide ion conductor made of a sintered body of _0.8 Sr _0.2 Ga _0.8 Mg _0.115 Co _0.085 O ₃ was prepared, and the electrical conductivity was measured by changing the temperature at an oxygen partial pressure of 10 ⁻⁵ atm. FIG. 11 shows the measurement results (Arrhenius plot of conductivity).

(Embodiment 3) In the same manner as in Embodiment 1, La
_1-x Sr _x Ga _0.8 Mg _0.115 Co _0.085 O ₃ (where x = 0.05, 0.1
, 0.15, 0.2, 0.25 or 0.3) were prepared, and the electrical conductivity was measured by changing the temperature or the oxygen partial pressure. FIG. 3 shows the relationship between the value of x at 950 ° C. and the electrical conductivity. Arrhenius plot of conductivity (oxygen partial pressure 10 ^-5 atm) and oxygen partial pressure dependence (temperature 95
0 ° C.) are shown in FIGS. 12 (a) and (b), respectively. It is noted that the behavior of the oxygen partial pressure dependency changes depending on the x value.

(Embodiment 4) In the same manner as in Embodiment 1, La _0.8
Sr _0.2 Ga _(1-yz) Mg _y Co _z O ₃ (where y + z = 0.05, 0.
(1, 0.15, 0.2, 0.25 or 0.3, y: z = 11.5: 8.5)
An oxide ion conductor made of a sintered body was prepared, and the electrical conductivity and the ion transport number were measured while changing the temperature. Each (y +
Arrhenius plot of conductivity at z) value (oxygen partial pressure
^10-5 atm) is shown in Fig. 4 (c). (Y + z) at 950 ° C
FIG. 4A shows the relationship between the value and the electric conductivity, and FIG. 4B shows the relationship between the ion transport number.

(Example 5) In the same manner as in Example 1, Ln _0.9
A composition of A _0.1 Ga _0.8 B1 _0.1 Co _0.1 O ₃ , Ln, A, B1
An oxide ion conductor made of a sintered body in which each metal atom was changed was prepared, and its electrical conductivity was measured. Oxygen partial pressure 10
The electric conductivity (σ / Scm ⁻¹ ) at ⁻⁵ atm and 950 ° C. was as follows.

Ln _0.9 Sr _0.1 Ga _0.8 Mg _0.1 Co _0.1 O ₃ Ln = La: 0.53 = Pr: 0.49 = Nd: 0.36 = Ce: 0.08 = Sm: 0.05 La _0.9 A _0.1 Ga _0.8 Mg _0.1 Co _0.1 O ₃ A = Sr: 0.53 = Ca: 0.24 = Ba: 0.22 La _0.9 Sr _0.1 Ga _0.8 B1 _0.1 Co _0.1 O ₃ B1 = Al: 0.12 = Mg: 0.53 = In: 0.23 (Example 6) As in Example 1, La _0.8 Sr _0.2 Ga _0.8 Mg
_An oxide ion conductor made of a sintered body of _0.2-z Fe _z O ₃ (z = _{0 to 0.2} ) was produced. The crystal structure of the obtained sintered body is represented by X
All were examined by line diffraction and found to have a perovskite crystal structure.

The results of measuring the electrical conductivity of this oxide ion conductor at a temperature of 950 ° C. and an oxygen partial pressure of 10 ⁻⁵ atm are shown in FIG.
As shown in FIG. From this figure, as described above, z =
It can be seen that high electric conductivity can be obtained in the range of 0.01 to 0.15. In addition, the temperature change and the oxygen partial pressure dependency of the electric conductivity when z = 0.03 in the above composition are as shown in FIGS. 7 (a) and 7 (b), respectively. It can be seen that this oxide ion conductor shows high electrical conductivity and ion transport number over a wide temperature range and a range of oxygen partial pressure.

[0082]

According to the present invention, the A-site which has not only higher oxide ion conductivity than stabilized zirconia which is a conventional representative oxide ion conductor but also has higher oxide ion conductivity is used. Compared to a quaternary composite oxide doped with only a non-transition metal at the B site, the oxide ion conductivity is higher and the ratio of the oxide ion conductivity to the electron conductivity, that is, the ion transport number is easier. In addition, an oxide ion conductor that can be freely controlled can be realized. Therefore, not only materials having a high electrical conductivity and a high ion transport number of 0.9 or more, which are useful as oxide ion conductors in a narrow sense,
Materials useful as mixed electron-ion conductors are also obtained.

The oxide ion conductor of the present invention having a high ion transport number can be used even at a lower temperature than stabilized zirconia, and exhibits high oxide ion conductivity under all oxygen partial pressures from an oxygen atmosphere to a hydrogen atmosphere. It is useful as an electrolyte for a solid oxide fuel cell, a gas sensor such as an oxygen sensor, and an oxygen separation membrane for an electrochemical oxygen pump, and may be able to realize a product with higher performance than before. Especially,
The oxide ion conductor represented by the above formula is very advantageous in that it maintains high oxide ion conductivity over a wide temperature range and a very wide oxygen partial pressure ranging from a pure oxygen atmosphere to a substantial hydrogen atmosphere. .

The oxide ion conductor of the present invention exhibiting mixed electron-ion conductivity can be used as an air electrode of a solid oxide fuel cell or a gas separation membrane utilizing a gas concentration difference. In particular, when an oxide ion conductor of the present invention exhibiting this electron-ion mixed conductivity is used as an air electrode, and a SOFC is constructed using the narrowly defined oxide ion conductor according to the present invention having a high ion transport number as an electrolyte, Since the interfacial resistance decreases, SO
FC output can be increased.

[Brief description of the drawings]

FIG. 1 shows a conventional representative oxide ion conductor and La _0.8 S
4 is a graph showing the electrical conductivity of a perovskite-type oxide ion conductor composed of a quaternary composite oxide having a composition of r _0.2 Ga _0.8 Mg _0.2 O ₃ .

FIG. 2 shows a comparison between the quaternary perovskite oxide ionic conductor of FIG. 1 and a quaternary composite oxide obtained by substituting a part of Mg with a transition metal. FIG.

FIG. 3 is a diagram showing an A atom (S) which is a doping atom of an A site in an oxide ion conductor comprising a quinary composite oxide according to the present invention.
3 is a graph showing the relationship between the ratio (x value) of r) and electric conductivity.

FIG. 4 (a) is a graph showing the ratio of the B-site doped atoms of the oxide ion conductor composed of a quinary composite oxide according to the present invention, that is, the total atomic ratio of (B1 + B2) atoms (y + z, However, y: z = 11.5: 8.5) is a graph showing the relationship between the electrical conductivity, and FIG. 4B is a graph showing the relationship between the above (y + z) value and the ion transport number. (c) is a graph showing the relationship between the electrical conductivity and the temperature of the oxide ion conductor composed of the quinary composite oxide having various (y + z) values, as in the above.

FIG. 5 shows the ratio (z-value) of B2 atoms, which are transition metals, among the B-site doped atoms of the oxide ion conductor comprising a 5/4 quaternary composite oxide according to the present invention, and the electrical conductivity and ion transport. It is a graph which shows the relationship with a rate.

FIG. 6 is a graph showing the electrical conductivity (950 ° C., oxygen partial pressure = 10 ⁻⁵ atm) of the composite oxide represented by La _0.8 Sr _0.2 Ga _0.8 Mg _0.2-z Fe _z O ₃ with respect to the z value. is there.

7 _{La 0.8 Sr 0.2 Ga 0.8 Mg 0.2} -z Fe z O of electric conductivity of the oxide ion conductor ₃ in the present invention shown oxygen partial pressure 10 ^-5 a
The temperature change at tm (a) and the oxygen partial pressure dependence at 950 ° C (b) are shown.

FIG. 8 is a schematic sectional view of a cell structure of a solid oxide fuel cell provided with surface irregularities.

FIG. 9 is an explanatory view showing an interface between an electrolyte layer and an air electrode of the above cell structure.

FIG. 10 is a graph showing the oxygen partial pressure dependence of the electrical conductivity of an oxide ion conductor composed of a quinary composite oxide according to the present invention.

FIG. 11 is a graph showing a temperature change of electric conductivity of an oxide ion conductor composed of another quinary composite oxide according to the present invention.

FIG. 12 is a graph showing the temperature change (a) and the oxygen partial pressure dependency (b) of the electrical conductivity of an oxide ion conductor comprising another quinary composite oxide according to the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01M 8/12 H01M 8/12

Claims (13)

[Claims] (1) General formula: Ln _1-x A _x Ga _1-yz B1 _y B2 _z O
An oxide ion conductor represented by ₃ . Wherein Ln = one or more of La, Ce, Pr, Nd, and Sm;
B1 = one or more of Mg, Al, In; B2 = one or more of Co, Fe, Ni, Cu; x = 0.05 to 0.3 Y = 0 to 0.29; z = 0.
01-0.3; y + z = 0.025-0.3. 2. The oxide ion conductor according to claim 1, wherein y ≧ 0.025 and z ≦ 0.15, which have high oxide ion conductivity. 3. The oxide ion conductor according to claim 1, which exhibits mixed electron-ion conductivity where z> 0.15. 4. Ln = La and / or Nd, A = Sr, B1 =
Mg, B2 = Co, x = 0.10 to 0.25, y = 0 to 0.17, z = 0.02
2. The oxide ion conductor according to claim 1, wherein 〜0.15 and y + z = 0.10〜0.25. 5. Ln = La, A = Sr, B1 = Mg, B2 = Fe, x =
0.1-0.3, y = 0.025-0.29, z = 0.01-0.15, y +
3. The oxide ion conductor according to claim 2, wherein z = 0.035 to 0.3. 6. x = 0.15 to 0.25, y = 0.09 to 0.24, z =
The oxide ion conductor according to claim 5, wherein 0.01 to 0.05 and y + z = 0.10 to 0.25. 7. A solid oxide fuel cell provided with an electrolyte comprising the oxide ion conductor according to claim 2. Description: 8. A solid oxide fuel cell comprising an air electrode containing the oxide ion conductor according to claim 3. 9. A solid oxide fuel comprising: an electrolyte comprising the oxide ion conductor according to claim 2; and an air electrode containing the oxide ion conductor according to claim 3. battery. (10) Ni and (2) a general formula: Ce _1-m C _m O ₂
(Wherein C represents one or more of Sm, Gd, Y and Ca, and m = 0.05 to 0.4), and has a fuel electrode comprising a compound represented by the formula: 2. The solid oxide fuel cell according to claim 1. 11. A gas sensor comprising the oxide ion conductor according to claim 2, 4, 5, or 6. 12. An oxygen separation membrane for an electrochemical oxygen pump, comprising the oxide ion conductor according to claim 2. 13. A gas separation membrane comprising the oxide ion conductor according to claim 3.