JPH11273451A - Oxide ion conductor, its manufacture and solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an oxide having high oxide ion conductivity at a relatively low temperature and to provide a fuel cell operating effectively at a low temperature with the oxide used as an electrolyte by using a ceria oxide with a specific composition. SOLUTION: Mixed powder of CeO2 , Ln2 O3 and Ca2 O3 is sintered at 1400-1600 deg.C to obtain the oxide expressed by the formula, where Ln is one or two or more kinds of elements selected from trivalent rare earth elements other than Ce. The oxide substituted with part of Ce by the trivalent rare earth elements Ln other than Ce has oxide ion conductivity by the action of the oxygen deficiency occurring in the ceria crystal structure. When the value of (x) is set to 0<x<=0.4 and the value of (y) is set to 0<y<0.05, the conductivity is increased and the conductivity of 0.075 S/cm at 800 deg.C can be obtained. When this oxide is used as the electrolyte material of a fuel cell, the fuel cell can be operated at 900 deg.C or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel oxide and a method for producing the same, and more particularly to a novel ceria-based oxide useful as an oxide ion conductor and a method for producing the same.

The present invention relates to an oxide ion conductor and a solid oxide fuel cell, and more particularly to an oxide ion conductor useful as an electrolyte material for a solid oxide fuel cell, an oxygen sensor, an oxygen pump, and the like. The present invention relates to a solid oxide fuel cell using an oxide ion conductor as an electrolyte.

[0003]

2. Description of the Related Art A ceria-based composite oxide containing Ce and a trivalent rare earth element other than Ce (for example, Sm) as a constituent element (cation) is known as a solid electrolyte because of its excellent oxide ion conductivity. In recent years, it has attracted attention as an electrolyte material for a fuel cell, an oxygen sensor, an oxygen pump, and the like. In particular, it is expected that the excellent conductive properties of ceria-based composite oxides will be effective in lowering the operating temperature of cells, which is one of the important issues for the practical use of solid oxide fuel cells. I have.

However, conventional ceria-based composite oxides generally have low sinterability, and when they are produced by a solid-phase reaction,
The raw material must be fired at a high temperature of around 1600 ° C, and the high firing temperature causes problems such as an increase in the cost required for firing and a decrease in the purity of the sintered body due to the progress of side reactions during the solid phase reaction. This has been a major obstacle to the practical use of ceria-based composite oxides.

[0005]

DISCLOSURE OF THE INVENTION The present invention overcomes such disadvantages in the production of the conventional ceria-based composite oxide, and provides a milder oxide ion conductor without deteriorating its properties as an ion conductor. An object of the present invention is to provide a novel ceria-based oxide that can be produced under conditions. An object of the present invention is to provide a method for producing a novel ceria-based oxide useful as an oxide ion conductor under mild conditions.

[0006] The present invention can be used at a relatively low temperature (for example, below 900 ° C, preferably below 850 ° C, more preferably below 800 ° C).
However, an object of the present invention is to provide an oxide ion conductor exhibiting high oxide ion conductivity. An object of the present invention is to provide a solid oxide fuel cell that can be operated effectively even at a relatively low temperature (for example, 900 ° C. or lower, preferably 850 ° C. or lower, more preferably 800 ° C. or lower).

[0007]

Means for Solving the Problems The present inventors have developed an oxide having an oxide ion conductive property equal to or higher than that of a conventional ceria-based composite oxide and useful as an oxide ion conductor under milder conditions. As a result of intensive studies to develop a manufacturing method under the following conditions, a ceria-based oxide containing Ce and a trivalent rare earth element other than Ce as a constituent element (cation), and further as a constituent element (cation), By adding a specific amount of Ga, it can be manufactured under milder conditions, and furthermore, it has been found that the obtained oxide has good characteristics as an oxide ion conductor, and the present invention has been completed. Reached.

That is, the present invention provides a compound represented by the general formula (1): (C
eO ₂₎ according to the _{1-x (LnO 1.5) xy} (GaO 1.5) oxide represented by _y. Ln is a trivalent rare earth element other than Ce (preferably a group consisting of Y, La, Pr, Nd, Sm and Gd)
One or two or more selected from x is 0 <x ≦
This value satisfies 0.4. y is a value satisfying 0 <y <0.05.

The present invention relates to CeO ₂ , Ln ₂ O ₃ and Ga ₂ O.
_3. A method for producing a ceria-based oxide, characterized in that the mixed powder of ( ₃₎ is sintered at 1400 to 1600 ° C. to obtain any one of the oxides. The present invention relates to CeO ₂ , Ln ₂ O ₃ and Ga ₂ O.
_A method for producing a ceria-based oxide, characterized in that the powder obtained by calcining the mixed powder of ( ₃ ) at 1000 to 1300 ° C and then pulverizing the mixture is sintered at 1400 to 1600 ° C to obtain any one of the oxides. According to.

[0010] The present invention resides in an oxide ion conductor comprising any one of the above oxides. The present invention relates to a solid oxide fuel cell using the oxide ion conductor as an electrolyte.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The oxide of the present invention (oxide ion conductor)
Electric complex) Complex oxide containing Ce and trivalent rare earth element (Ln) other than Ce as a constituent element (cation), that is, C in ceria
An oxide in which a part of e is substituted with a trivalent rare earth element (Ln) other than Ce has a fluorite-type crystal structure corresponding to a crystal structure in which an oxygen defect has occurred in the ceria crystal structure. It is thought that the oxide ion conductivity is exhibited by the action of oxygen vacancies.

As trivalent rare earth elements (Ln) other than Ce, for example, Sc, Y, La, lanthanide elements (P
r, Nd, Sm, Eu, Gd, Tb, Dy, Ho, E
r, Tm, Yb, Lu, etc.) and one or more trivalent rare earth elements selected from the group consisting of Ac and the like.
In a preferred embodiment, the trivalent rare earth elements (Ln) other than Ce include Y, La, Pr, Nd, Sm and Gd.
One or more selected from the group consisting of

A general formula (1) corresponding to the substitution ratio of Ce to a trivalent rare earth element (Ln) other than Ce for ceria
The upper limit of the value of x is 0.4 or less, preferably 0.3 or less, more preferably 0.299 or less, further preferably 0.29 or less, further preferably 0.27 or less, particularly preferably 0.25 or less, and still more preferably 0.23 or less. The lower limit of the value of x is a value exceeding 0, preferably 0.001 or more, more preferably 0.01
Above, more preferably 0.05 or more, particularly preferably 0.1 or more, and still more preferably 0.15 or more. The value of x is 0.4
If it exceeds, the conductivity tends to rapidly decrease.

Ce, a trivalent rare earth element other than Ce (L
The oxide of the present invention, which is a composite oxide containing n) and Ga as constituent elements (cations), is produced by, for example, a sintering reaction that proceeds simultaneously with a solid phase reaction when the raw material mixed powder is produced by a solid phase reaction. It is considered that Ga acts to increase the grain growth rate when a suitable ceria-based composite oxide is formed.

The upper limit of the value of y in the general formula (1) corresponding to the substitution ratio of Ce to Ga for ceria is less than 0.05, preferably 0.049 or less, more preferably 0.04 or less, further preferably 0.03 or less, particularly preferably 0.03 or less. 0.02 or less. y
Is a value exceeding 0, preferably 0.001 or more, more preferably 0.004 or more, and still more preferably 0.07 or more. When the value of y is 0.05 or more, a side reaction between Ga and a trivalent rare earth element (Ln) other than Ce proceeds at the time of production, and impurities (for example, a garnet-type compound represented by Ga ₅ Ln ₃ O ₁₂ ) ) A phase is generated and the crystal structure does not become a single fluorite type phase. As a result, grain growth tends to be suppressed and conductivity tends to decrease.

The oxide of the present invention is useful as an oxide ion conductor. Conductivity at 1000 ° C. is 0.15 S / cm or more, preferably 0.18 S / cm or more, more preferably 0.2 S / cm or more.
/ Cm or more of the present invention is particularly useful as an oxide ion conductor, specifically as an electrolyte material for a solid oxide fuel cell.

An electric conductivity at 800 ° C. of 0.075 S / cm or more;
Preferably 0.08 S / cm or more, more preferably 0.085 S / c
m or more, more preferably 0.09 S / cm or more of the oxide of the present invention, as an oxide ion conductor, specifically, a relatively low temperature (eg 900 ° C. or less, preferably 850 ° C. or less,
It is particularly useful as an electrolyte material for a solid oxide fuel cell operated at 800 ° C. or lower.

The absolute density (25 ° C.) by the Archimedes method is
6.6 or more, preferably 6.7 or more, more preferably 6.8 or more, 7 or less, preferably 6.99 or less, more preferably
The oxide of the present invention of 6.98 or less tends to have high conductivity, and is particularly useful as an oxide ion conductor.

The oxide of the present invention having a relative density of 97% or more has high density and low oxygen gas permeability, and is therefore particularly useful, for example, as an electrolyte material for a solid oxide fuel cell. Here, the relative density is a relative value obtained by dividing the absolute density (25 ° C.) by the Archimedes method by the theoretical density calculated from the lattice constant.

A porosity of 10% or less, preferably 8% or less;
The oxide of the present invention, more preferably 6% or less, still more preferably 5.5 or less (usually 0.5% or more, further 1% or more, particularly 1.5% or more) has high denseness and oxygen gas permeability. Therefore, it is particularly useful, for example, as an electrolyte material for a solid oxide fuel cell.

Here, the porosity is determined by an electron micrograph obtained by using a sample obtained by subjecting a mirror-polished surface of the oxide of the present invention to thermal etching and then coating a thin film of a conductive substance (for example, Pt-Pd). And prepare a grid on it (normal grid points: 357 points per photo)
It can be obtained by counting the intersections between the lattice points and the pores and dividing by the total number of lattice points.

The density of the oxide can be determined by, for example, assembling a solid oxide fuel cell using the oxide as an electrolyte material and measuring the open circuit voltage. For example, if the density of the oxide used as the electrolyte material is not sufficient, oxygen and hydrogen are short-circuited in the electrolyte, so that the theoretical electromotive force is not obtained.

The average particle size is 2 μm or more, preferably 4 μm
Or more, more preferably 6 μm or more, still more preferably 8 μm
m or more (usually 30 μm or less, further 25 μm or less, especially
The oxide of the present invention having a particle size of 20 μm or less is particularly useful as an oxide ion conductor.

Here, the average particle size is defined as an electron micrograph obtained by using a sample obtained by coating a thin film of a conductive substance (for example, Pt-Pd) after subjecting a mirror-polished surface of the oxide of the present invention to thermal etching. Prepare three sheets, and draw at least 10 straight lines with a length of about 70 μm at any position and in any direction on each photo. Measure the length of each straight line traversing the grain one by one. By averaging 1.5 times
You can ask.

The absolute density, relative density, porosity, average particle size and the like of the oxide of the present invention are determined by, for example, x in the general formula (1) according to the type of the trivalent rare earth element (Ln) other than Ce. And y
By adjusting the value of, the production conditions (eg,
In the case of manufacturing by a solid-phase reaction method, it can be controlled by adjusting the firing temperature or the like.

Method for Producing Oxide of the Present Invention (1) Solid State Reaction Method The oxide of the present invention can be produced based on the solid state reaction method. For example, an oxide of each constituent cation (Ce)
O ₂ , Ln ₂ O ₃ , Ga ₂ O _3, etc.) or an oxide capable of forming these oxides by firing (for example, carbonate, etc.) in a predetermined molar ratio so as to have a composition satisfying the general formula (1). The oxide of the present invention can be produced by calcining the raw material mixture mixed at a predetermined ratio at a predetermined temperature for a predetermined time.

By calcining the mixed raw material at a temperature lower than the firing temperature for a predetermined time before firing, an oxide having a more uniform composition can be easily produced. The raw material mixture can be calcined or fired after the powder is pressed at a predetermined temperature for a predetermined time. When calcining the raw material mixture, the calcined raw material mixture can be pulverized, pressed at a predetermined temperature for a predetermined time, and then fired.

The sintering temperature is, for example, 1300 ° C. or higher, preferably 1400 ° C. or higher, and is usually lower than the temperature at which melting is not completely completed, specifically 1600 ° C. or lower, preferably 1500 ° C. or lower. The firing time can be, for example, 5 hours or more, preferably 10 hours or more, more preferably 15 hours or more, and usually 30 hours or less, preferably 24 hours or less.

If the firing temperature is low (for example, lower than 1400 ° C., particularly lower than 1300 ° C.), sintering becomes difficult to proceed, densification becomes insufficient, and pores tend to remain in the sintered body. When pores are left in the sintered body, the remaining pores increase the resistance at the grain boundaries of the crystal grains,
As a result, the conductivity of the sintered body is lowered, which is not preferable.

Conversely, if the firing temperature is high (for example, higher than 1500 ° C., especially higher than 1600 ° C.), intense grain growth tends to occur, and a large amount of pores tends to be left at the grain boundary. , The density of the sintered body decreases,
As a result, the conductivity of the sintered body decreases, which is not preferable.

The calcination temperature can be, for example, 900 ° C. or higher, preferably 1000 ° C. or higher, and is usually 1400 ° C. or lower, preferably 1300 ° C. The calcination time can be, for example, at least 12 hours, preferably at least 18 hours, usually at most 48 hours, preferably at most 36 hours, specifically about 24 hours.

If the calcination temperature is low (for example, lower than 1000 ° C., especially lower than 900 ° C.), the solid phase reaction tends to be difficult to proceed, and if it is higher (for example, higher than 1400 ° C., particularly
If the temperature is higher than 1300 ° C.), sintering tends to proceed too much and many pores tend to be formed. If many pores are formed, the conductivity of the sintered body tends to be lowered as a result, which is not preferable.

The method of pressure-forming the raw material mixture or the calcined and pulverized raw material mixture is not particularly limited, and a known method can be used.
It can be molded at a pressure of 500 to 1500 kgf / cm ² , and if necessary, can be further molded by an isotropic hydrostatic press to 2000 to 30 kgf / cm ^2.
It can be formed at a pressure of about 00 kgf / cm ² .

(2) Thin Film Formation Method The oxide of the present invention can be produced as a thin film by a known method for depositing a metal oxide thin film from a gas phase. The oxide thin film of the present invention can be formed, for example, by a PVD method such as a vacuum evaporation method, a sputtering method, and an ion plating method.
It can be manufactured by a CVD method such as a thermal CVD method, a plasma CVD method, or a laser CVD method, or a thin film forming method such as a thermal spraying method.

Solid Electrolyte Fuel Cell A solid electrolyte fuel which can be operated even at a relatively low temperature range by using the oxide ion conductor comprising the oxide of the present invention as an electrolyte of a solid electrolyte fuel cell. A battery can be provided.

A solid oxide fuel cell comprises an electrolyte and electrodes (anode and cathode) provided in contact with the electrolyte as main components, and a fuel (eg, hydrogen, natural gas, methanol, coal, etc.) is provided on the anode side of the electrolyte. Gas) and air (oxygen) to the cathode side, the oxygen supplied to the cathode side receives electrons from the cathode to become oxide ions, which diffuse in the electrolyte and become Side and reacts with the fuel supplied to the anode side. At this time, the electrons leave the oxide ions, pass through the load of the external circuit, and reach the cathode.

As a solid oxide fuel cell, for example,
A cylindrical solid electrolyte fuel cell having a structure in which a cathode layer, an electrolyte layer, and an anode layer are sequentially formed and laminated on a cylindrical surface of a cylindrical support tube, and an anode layer is formed on one of both surfaces of a flat electrolyte layer. There is a flat solid electrolyte fuel cell having a structure in which a cathode layer is formed on the other side and having a structure in which a stack is sequentially stacked via a separator. The oxide ion conductor of the present invention can be used as an electrolyte of any type of solid oxide fuel cell.

The thickness of the electrolyte layer depends on the characteristics required for the solid oxide fuel cell, the mechanical strength required for the electrolyte layer,
In consideration of the conductivity of the oxide ion conductor used as the electrolyte, it can be appropriately selected and is not particularly limited, but is generally 1 mm or less, preferably 500 μm or less, more preferably 200 μm or less, furthermore It is preferably 100 μm or less, usually 5 μm or more, preferably 10 μm or more, more preferably 30 μm or more, and still more preferably 50 μm or more.

The electrolyte layer made of the oxide ion conductor of the present invention can be formed by, for example, a sheet forming sintering method which is a conventional ceramic process.
For example, it can be formed on a gas permeable porous substrate by a thin film forming method such as a CVD method, a thermal spraying method or a thermal spraying method. Since the oxide (oxide ion conductor) of the present invention can be produced by a sintering method at a relatively low temperature (for example, 1600 ° C. or less, particularly 1500 ° C. or less), co-sintering with an electrode material is performed. It can also be manufactured by a method or the like.

As the anode and the cathode, for example,
An electron conductive material that is a porous material having a porosity of about 30% and is stable in fuel and air can be used. By using a porous body as an electrode, electrolyte / electrode /
The reaction can be performed at the three-phase interface of the gas phase (fuel and air), and the reaction field can be increased by increasing the area of the three-phase interface.

As the anode, for example, Ni and Y ₂ O ₃
It can be used a composite material with stabilized ZrO ₂ (Ni-YSZ cermet). As the cathode, for example, a (LaSr) MnO ₃ -based material can be used.

[0042]

The oxide of the present invention is obtained by adding a small amount of an oxide composed of trivalent gallium (Ga ³⁺ ) as a third component cation to a solid-state reaction system of a ceria-based oxide.
Since the grain growth is remarkably promoted during the production by the solid-phase reaction, a dense sintered body can be obtained even under mild conditions in which the firing temperature is reduced.

The oxide of the present invention has a relatively low temperature (for example,
900 ° C or less, preferably 850 ° C or less, more preferably 800
℃ or less), since it has sufficiently good ionic conductivity as an electrolyte of a solid oxide fuel cell, it has a relatively low temperature (for example, 900 ℃ or less, preferably 850 ℃ or less, more preferably 800 ℃ or less The present invention is useful as an electrolyte of a solid oxide fuel cell that can be operated in the following, and can also be used as an oxygen sensor and an oxygen pump.

[0044]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Examples 1 to 5 [Ln: Sm, y: 0.002 to
0.01, firing temperature: 1400-1600 ° C] CeO ₂ (Shin-Etsu Chemical Co., Ltd., purity 99.99%), S
m ₂ O ₃ (Shin-Etsu Chemical Co., Ltd., purity 99.9%) and G
Powder of a ₂ O ₃ (purity: 99.99%, manufactured by Kojundo Chemical Laboratory) was weighed and mixed so as to have the composition shown in Table 1. The obtained raw material mixture was mixed and pulverized by a ball mill in ethanol for 24 hours, then ethanol was removed, and then dried at 100 ° C.

The obtained raw material mixed powder was transferred to a crucible, calcined in an electric furnace in an air atmosphere at 1000 ° C. for 18 hours, pulverized, pressed (500 kgf / cm ² ) and isostatically pressed (3
000 kgf / cm ² ) to obtain a green body before firing. The obtained green body before firing was fired at the firing temperature shown in Table 1 for 24 hours to obtain a sintered body (the oxide of the present invention).

The obtained sintered body was identified by powder X-ray diffraction measurement. FIG. 1 shows the result (chart) of the powder X-ray diffraction measurement of the sintered body (Examples 2, 4, and 5) obtained by firing at 1500 ° C.

A scanning electron microscope (SEM) of a sample obtained by subjecting the surface of the obtained sintered body to mirror polishing, performing thermal etching at a temperature lower than the firing temperature by 100 ° C., and then applying Pt—Pd coating. From the photograph, the average particle size was measured. Table 1 shows the results. FIG. 2 shows the relationship between the sintering temperature and the average particle size for the sintered body with y: 0.01 (Examples 1 to 3). FIG. 3 shows the relationship between the value of y and the average particle size of the sintered bodies (Examples 2, 4, and 5) obtained by firing at 1500 ° C. A scanning electron microscope (SEM) photograph of the sintered body obtained in Example 2 is shown in a reference photograph.

The density of the obtained sintered body was determined by the Archimedes method. Table 1 shows the results. FIG. 4 shows the relationship between the value of y and the density of the sintered body (Examples 2, 4, and 5) obtained by firing at 1500 ° C.

The obtained sintered body was ground and subjected to surface polishing, and four platinum wires were wound around a 3 mm × 3 mm × 20 mm rectangular parallelepiped sample, and a platinum paste was applied and fixed. The conductivity was measured at 800 ° C. in air by a DC four-terminal method using a sample prepared by baking at 1000 ° C. for 30 minutes. Table 1 shows the results
Shown in A sintered body obtained by firing at 1500 ° C. (Example 2,
4 and 5), the relationship between the value of y and the conductivity is shown in FIG.

Example 6 [Ln: Gd, y: 0.01, firing temperature
Degree: 1500 ° C.] The procedure of Example 2 was repeated except that Gd ₂ O ₃ (purity: 99.9%, manufactured by Shin-Etsu Chemical Co., Ltd.) was used instead of the Sm ₂ O ₃ powder. Table 1 shows the results.

Example 7 [Ln: Y, y: 0.01, firing temperature
Degree: 1500 ° C.] The same procedure as in Example 2 was carried out except that Y ₂ O ₃ (purity: 99.9%, manufactured by Yttrium Japan Ltd.) was used instead of the Sm ₂ O ₃ powder. Table 1 shows the results.

Comparative Example 1 [Ln: Sm, y: 0.05, firing temperature
Degree: 1500 ° C] CeO ₂ (Shin-Etsu Chemical Co., Ltd., purity 99.99%), S
m ₂ O ₃ (Shin-Etsu Chemical Co., Ltd., purity 99.9%) and G
The procedure was the same as in Example 2 except that a raw material mixture was used in which a ₂ O ₃ powder (purity: 99.99%, manufactured by Kojundo Chemical Laboratory) was weighed and mixed to obtain the composition shown in Table 1. The results are shown in Table 1 and FIGS. 1, 3, 4, and 5. In FIG.
For the sintered body of Comparative Example 1, a diffraction peak attributed to Ga ₅ Sm ₃ O ₁₂ appears.

Comparative Examples 2 to 4 [Ln: Sm, y: 0, firing
Temperature: 1500-1700 ° C.] Powder of CeO ₂ (Shin-Etsu Chemical Co., Ltd., purity 99.99%) and Sm ₂ O ₃ (Shin-Etsu Chemical Co., Ltd., purity 99.9%) were prepared so as to have the composition shown in Table 1. The same procedure as in Examples 1 to 5 was carried out except that the raw material mixture weighed and mixed was used, and the firing temperature was set at 1500 to 1700 ° C. The results are shown in Table 1, FIGS. 1 to 5 and reference photographs.

Comparative Examples 5.6 [Ln: Gd, y: 0, firing]
Temperature: 1500 to 1600 ° C] CeO ₂ (Shin-Etsu Chemical Co., Ltd., purity 99.99%) and Gd ₂ O ₃ (Shin-Etsu Chemical Co., Ltd., purity 99.9%) powders were prepared so as to have the composition shown in Table 1. The same procedure as in Examples 1 to 5 was carried out except that the raw material mixture weighed and mixed was used, and the firing temperature was set at 1500 to 1700 ° C. Table 1 shows the results.

[0056]

TABLE 1 Composition of oxide (oxide ion conductor) Firing temperature average particle size Density Conductivity (800 ° C) (° C) Example 1 (CeO ₂ ) _0.8 (SmO _1.5 ) _0.19 (GaO _1.5 ) _0.01 1400 2.81 μm 6.86 g / cm ³ 7.88 × 10 ^-2 S / cm Example 2 (CeO ₂ ) _0.8 (SmO _1.5 ) _0.19 (GaO _1.5 ) _0.01 1500 9.62 μm 6.93 g / cm ³ 8.69 × 10 ^-2 S / cm Example 3 (CeO ₂ ) _0.8 (SmO _1.5 ) _0.19 (GaO _1.5 ) _0.01 1600 19.77 μm 6.66 g / cm ³ 8.42 × 10 ^-2 S / cm Example 4 (CeO ₂ ) _0.8 (SmO _1.5 ) _0.198 (GaO _1.5 ) _0.002 1500 11.46 μm 6.96 g / cm ³ 9.06 × 10 ^-2 S / cm Example 5 (CeO ₂ ) _0.8 (SmO _1.5 ) _0.195 (GaO _1.5 ) _0.005 1500 11.39 μm 6.99 g / cm ³ 8.96 × 10 ^-2 S / cm Example 6 (CeO ₂ ) _0.8 (GdO _1.5 ) _0.19 (GaO _1.5 ) _0.01 1500 6.61 μm 7.06 g / cm ³ 8.42 × 10 ^-2 S / cm Example 7 (CeO ₂ ) _0.8 (YO _1.5 ) _0.19 (GaO _1.5 ) ^{_{) 0.01 1500 5.13μm 6.48g / cm 3}} 7.12 × 10 -2 S / cm Comparative example _{1 (CeO 2) 0.8 (SmO} 1.5) 0.15 (Ga _{1.5) 0.05 1500 7.18μm 7.00g / cm} 3 7.46 × 10 -2 S / cm Comparative Example _{2 (CeO 2) 0.8 (SmO} 1.5) 0.2 1500 2.86μm 6.84g / cm 3 7.52 × 10 -2 S / cm Comparative Example 3 (CeO ₂ ) _0.8 (SmO _1.5 ) _0.2 1600 5.42 μm 7.02 g / cm ³ 8.92 × 10 ^-2 S / cm Comparative Example 4 (CeO ₂ ) _0.8 (SmO _1.5 ) _0.2 1700 11.82 μm 6.96 g / cm ³ 8.41 × 10 ^-2 S / cm Comparative Example 5 (CeO ₂ ) _0.8 (GdO _1.5 ) _0.2 1500 1.79 μm 6.79 g / cm ³ 6.94 × 10 ^-2 S / cm Comparative Example 6 (CeO ₂ ) _0.8 (GdO _1.5 ) _0.2 1600 4.36 μm 6.93 g / cm ³ 8.62 × 10 ^-2 S / cm

[Brief description of the drawings]

FIG. 1 is a chart showing the results of powder X-ray diffraction measurement of oxide sintered bodies produced in Examples 2, 4 and 5, and Comparative Examples 1 and 2.

FIG. 2 Oxides of Examples 1 to 3: (CeO ₂ ) _0.8 (Sm
_{O 1.5) 0.19 (GaO 1.5)} 0.01 and Comparative Examples 2 to 4 of oxides: (a graph showing the relationship between the average particle diameter of the CeO _{2) 0.8} (SmO _1.5) sintering temperature for _0.2 and sintered body.

FIG. 3 is a graph showing the relationship between the added mol% of gallium (the value of y in the general formula (1)) and the average particle diameter of the oxides of Examples 2, 4 and 5, and Comparative Examples 1 to 3. is there.

FIG. 4 shows the addition mol% of gallium (the value of y in the general formula (1)), the absolute density and the porosity of the sintered body with respect to the oxides of Examples 2, 4 and 5, and Comparative Examples 1 to 3. 6 is a graph showing the relationship of.

FIG. 5 shows the addition percentage of gallium (the value of y in the general formula (1)) of the oxides of Examples 2, 4 and 5, and Comparative Examples 1 to 3, and the conductivity of the sintered body at 800 ° C. 6 is a graph showing a relationship with the graph.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junichi Fujita 3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Kansai Electric Power Company

Claims (12)

[Claims] 1. The general formula (1): (CeO ₂ ) _1-x (Ln
Oxide represented by O _1.5 ) _xy (GaO _1.5 ) _y [Ln is Ce
And at least one element selected from trivalent rare earth elements other than the above, and 0 <x ≦ 0.4 and 0 <y <0.05]. 2. The oxide according to claim 1, wherein Ln is one or more elements selected from the group consisting of Y, La, Pr, Nd, Sm and Gd. 3. The method according to claim 1, wherein the crystal structure is a fluorite type.
The oxide according to the above. 4. The oxide according to claim 1, which has a conductivity at 1000 ° C. of 0.15 S / cm or more. 5. The oxide according to claim 1, which has an electric conductivity at 800 ° C. of 0.075 S / cm or more. 6. The oxide according to claim 1, which has an absolute density of 6.6 to 7 at 25 ° C. 7. The method according to claim 1, wherein the relative density is 97% or more.
The oxide according to any one of the above. 8. The method according to claim 1, wherein the average particle size is 2 μm or more.
8. The oxide according to any of 7. 9. An oxide according to claim 1, wherein a mixed powder of CeO ₂ , Ln ₂ O ₃ and Ga ₂ O ₃ is sintered at 1400 to 1600 ° C. A method for producing a ceria-based oxide. 10. A powder obtained by calcining a mixed powder of CeO ₂ , Ln ₂ O ₃ and Ga ₂ O ₃ at 1000 to 1300 ° C. and then pulverizing the powder at 1400 to 1600 ° C. 8. A method for producing a ceria-based oxide, comprising obtaining the oxide according to any one of 8. 11. An oxide ion conductor comprising the oxide according to claim 1. Description: 12. A solid oxide fuel cell comprising the oxide ion conductor according to claim 11 as an electrolyte.