JPH08198670A - Fluorite type zirconia based solid electrolite - Google Patents

Abstract

PURPOSE: To suppress the formation of C type rare earth element compd., to increase the amount of oxygen flaw and to increase oxygen ion concn. by partially replacing a Y site being a tervalent rear earth element with a univalent or bivalent element and forming a solid solution. CONSTITUTION: A precipitate is obtained by adding a precipitating agent to an inorg. salt aq. soln. of a metallic element containing yttrium, an alkali metal, magnesium or barium and zirconium. This precipitate is filtered and dried, and then burned to produce a defective fluorite type solid electrolyte expressed by formula ((Y1-a Ma )x Zr1-x )02-y (M is a univalent alkali metal. Mg and Ba; (a), (x) and (y) are an actual number satisfying 0.30<(a)<0.67; 0.12<(x)<0.35; 0.78<(y)<0.41).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorite-type zirconia-based solid electrolyte material having a large amount of oxygen defects.

[0002]

_2. Description of the Related Art ZrO ₂ belongs to the fluorite type compound, and 4
Trivalent rare earth elements (Y, Yb, Sc)
And the like) are solid-dissolved to form a solid electrolyte material exhibiting high oxygen ion conductivity by introducing oxygen defects (NQ Minh, J. Am. Ceram.
Soc. , Vol. 76, 3, 563-88 (198
8)).

[0003]

Such a defective zirconia-based solid electrolyte causes oxygen defects by substituting solid solution of trivalent rare earth elements into tetravalent Zr sites. When the solid solution amount of the trivalent element is increased to increase the amount, the conductivity decreases due to the formation of C-type rare earth compound and the ordering (or association) of oxygen defects, so that the oxygen ion conductivity is improved. It was a difficult situation.

[0004]

Means for Solving the Problems The present inventors have conducted extensive studies to solve the above problems. As a result, in the above-mentioned defective zirconia-based solid electrolyte, the Y site, which is a trivalent rare earth element, is partially replaced with a monovalent or divalent element to form a solid solution, so that the Y site has a trivalent average valence. The following low valence suppresses the formation of a C-type rare earth compound, which is a solid solution of rare earth oxide and ZrO ₂ , which causes a decrease in conductivity, increases the amount of oxygen vacancies, and increases the valence of 1 or 2. A solid electrolyte having a high oxygen ion conductivity by solid-dissolving an element having a larger ionic radius than Y, which is a valence, to expand the lattice and increase the space in the crystal lattice through which oxygen ions can pass. The inventors have found that it is possible to provide materials, and have completed the present invention.

[0005] The present invention has the following general formula _{(1) {(Y 1-} a M a) x Zr 1-x} O 2-y (1) ( wherein, M represents a monovalent alkali metal or Mg or Ba
Where a, x and y are 0.30 <a <0.67, 0.
Represents a real number that satisfies 12 <x <0.35 and 0.078 <y <0.41. Defective fluorite structure type solid electrolyte represented by), and the following general formula _{(2) {(Y 1-} a M a) x (Zr 1-b N b) 1-x} O 2-y (2) ( Formula In the formula, M and N represent monovalent alkali metal or Mg or Ba, and M ≠ N. A, x, b and y are 0.30 <a.
<0.67, 0.16 <x <0.27, 0 <b <0.5
And a real number satisfying 0.18 <y <0.87. ) Fluorite type solid electrolyte represented by.

Next, the present invention will be described in more detail.

[0007] ZrO ₂ based solid electrolyte of the present invention is represented by the following general formula _{(1) {(Y 1-} a M a) x Zr 1-x} O 2-y (1) ( wherein, M is a monovalent Alkali metal or Mg or Ba
Where a, x and y are 0.30 <a <0.67, 0.
Represents a real number that satisfies 12 <x <0.35 and 0.078 <y <0.41. ).

In the above general formula (1), if Sr or Ca, which is a divalent alkaline earth metal element, is used as M, ZrO
_In order to form SrZrO ₃ or CaZrO _{3 as a} by-product between the _two , Z consisting of a fluorite single phase
It is not preferable because the rO ₂ -based high ionic conductor cannot be produced and the ionic conductivity is lowered.

When the value of a is 0.30, the amount of oxygen defects is small and a sufficiently high oxygen ion conductivity cannot be obtained. When the value of a is 0.67 or more, a monovalent alkali metal element or The Mg element or the Ba element cannot be completely dissolved, is precipitated at the grain boundary, reacts with the glass phase slightly contained in the raw material to increase the resistance at the grain boundary, and is preferable because it lowers the oxygen ion conductivity of the entire electrolyte. Absent.

When the value of x is 0.12 or less, the amount of oxygen defects is insufficient and a sufficiently high oxygen ion conductivity cannot be obtained. When the value of x is 0.35 or more, the amount of oxygen defects increases. Zr
As compared with the above, the amount of solid solution of Y having a large ionic radius increases and the lattice expands, but the ionic conductivity remarkably decreases, which is not preferable. Although the reason for this has not been clearly clarified, it is mentioned that the characteristics of the ZrO ₂ -based solid electrolyte are that oxygen vacancy association is likely to occur. It is thought that the degree will decrease.

The value of y is a value determined so as to balance the values of positive charges and negative charges when determining the values of a and x, and is a value of 0.078 to 0.41.

By selecting the above composition, it becomes possible to produce a ZrO ₂ type high ionic conductor consisting of a single phase of fluorspar.

[0013] ZrO ₂ based solid electrolyte of the present invention is represented by the following general formula _{(2) {(Y 1-} a M a) x (Zr 1-b N b) 1-x} O 2-y (2) ( In the formula, M and N represent a monovalent alkali metal or Mg or Ba, M ≠ N, and a, x and y are 0.30 <a <.
Represents a real number satisfying 0.67, 0.16 <x <0.27, 0 <b <0.5 and 0.18 <y <0.87. ).

In the general formula (2), if Sr or Ca, which is a divalent alkaline earth metal element, is used as M and N, Z
Since SrZrO ₃ or CaZrO ₃ is produced as a by-product with rO _2, it is not possible to produce a ZrO ₂ based high ionic conductor consisting of a fluorite single phase, and the ionic conductivity decreases. Not good for

When the value of a is 0.30 or less, the amount of oxygen defects is small and a sufficiently high oxygen ion conductivity cannot be obtained, and when the value of a is 0.67 or more, a monovalent alkali metal or 2 at the Y site is used. In order to reduce the oxygen ion conductivity of the entire electrolyte by increasing the resistance at the grain boundary by reacting with the glass phase contained in the raw material to a small extent, the valent Mg or Ba element cannot be completely dissolved and precipitates at the grain boundary. Not preferable.

When the value of x is 0.16 or less, the amount of oxygen defects is insufficient and a sufficiently high oxygen ion conductivity cannot be obtained, and when the value of x is 0.27 or more, the amount of oxygen defects increases. Zr
As compared with the above, the amount of solid solution of Y having a larger ionic radius increases, so that the lattice expands, but it is not preferable because it significantly reduces the ionic conductivity. The reason for the decrease in ionic conductivity is Z
A feature of the rO ₂ -based solid electrolyte is that oxygen vacancy association is likely to occur, and it is considered that the number of oxygen vacancies apparently decreases and the ionic conductivity decreases in the above range.

When the value of b is 0, it corresponds to the above general formula (1). When the value of b is 0.5 or more, the monovalent alkali metal element or the divalent Mg element or Ba element cannot be completely dissolved in the Zr site and precipitates at the grain boundary to form a glass phase slightly contained in the raw material. It is not preferable because it reacts to increase the resistance at the grain boundary and lowers the oxygen ion conductivity of the entire electrolyte.

The value of y is a value determined so as to balance the values of positive charge and negative charge when determining the values of a and x, and is a value of 0.18 to 0.87.

By selecting the above composition, it becomes possible to produce a ZrO ₂ high ionic conductor composed of a fluorite single phase.

The synthesis method of the present invention is not particularly limited, and a method of mixing oxides as a raw material powder by dry and wet mixing, followed by firing, an aqueous solution of an inorganic salt as a raw material, and oxalic acid as a precipitating agent, etc. A precipitate is prepared as a carbonate by using the above method, and the precipitate is filtered, dried and then calcined, or the alkoxide method is used in which an alkoxide solution is used as a raw material. Then, the precipitate can be synthesized by a method such as filtration, drying, and baking.

The mechanism of the effects of the present invention has not been fully clarified yet, but when a trivalent rare earth element is simply dissolved in ZrO ₂ as a solid solution, the C-type rare earth compound is increased by increasing oxygen deficiency. However, by partially replacing the monovalent or divalent Mg or Ba element with the trivalent rare earth element site to form a solid solution, the C type rare earth compound is not generated. It is considered that the oxygen ionic conductivity is improved due to the effect of increasing the amount of oxygen defects and also increasing the bottleneck diameter by increasing the lattice volume.

[0022]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Examples 1 to 13 Yttrium oxide powder (manufactured by Shin-Etsu Chemical), cesium carbonate powder (manufactured by Kishida Chemical), sodium carbonate (manufactured by Kishida Chemical)
Rubidium carbonate (manufactured by Kishida Chemical), zirconium oxide powder (manufactured by Toso), magnesium oxide (manufactured by Kishida Chemical),
Barium carbonate (manufactured by Kishida Chemical Co., Ltd.) and lithium oxide powder (manufactured by Kishida Chemical Co., Ltd.) were ball-mill mixed in ethanol, and then calcined in air at 1000 ° C. for 1 h,
This powder was formed into pellets by hydrostatic pressure of ² t / cm ² . A cubic phase fluorite single-phase sintered body was produced by sintering the obtained sample in air at 1500 ° C. for 4 hours.

Example 1: {(Y _0.5 Na _0.5 ) _0.28 Zr _0.72 } O _1.72 Example 2: {(Y _0.5 Cs _0.5 ) _0.32 Zr _0.68 } O _1.68 Example 3: {(Y _0.5 Na _0.5 ) _0.15 Zr _0.75 } O _1.65 Example 4: {(Y _0.4 Na _0.6 ) _0.28 Zr _0.72 } O _1.69 Example 5: {(Y _0.6 Na _0.4 ) _0.28 Zr _0.72 } O _1.75 Example 6: {(Y _0.5 Na _0.5 ) _0.2 (Zr _0.67 Li _0.33 ) _0.8 } O
_1.40 Example 7: {(Y _0.5 Cs _0.5 ) _0.2 (Zr _0.67 Rb _0.33 ) _0.8 }
O _1.40 Example 8: {(Y _0.5 Mg _0.5 ) _0.28 Zr _0.72 } O _1.79 Example 9: {(Y _0.5 Ba _0.5 ) _0.28 Zr _0.72 } O _1.79 Example 10: {(Y _0.5 Na _0.5 ) _0.18 (Zr _0.67 Li _0.33 ) _0.82 } O
_1.41 Example 11: {(Y _0.5 Na _0.5 ) _0.24 (Zr _0.67 Li _0.33 ) _0.76 } O
_1.38 Example _{12: {(Y 0.4 Na 0.6} ) 0.2 (Zr 0.8 Li 0.2) 0.8} O 1.54 Example _{13: {(Y 0.6 Na 0.4} ) 0.2 (Zr 0.6 Li 0.4) 0.8} O 1.34 However, the above oxygen The number is a value calculated from the balance of positive and negative charges.

The obtained sintered body was coated with a platinum electrode and
After baking the electrode at 000 ° C., the complex impedance was measured by the AC two-terminal method, and the ionic conductivity was calculated by the following formula (3).

Ionic conductivity: log σ = log {Z cos θ / (l · S ^-1 )} (3) (where σ is conductivity (ionic conductivity is expressed as a logarithm of this value) and Z is impedance) , Θ is the lag angle, l is the thickness of the pellet, and S is the area of the platinum electrode on the pellet.) Table 1 shows the values of conductivity at 950 ° C.

[0027]

[Table 1]

Comparative Examples 1 to 10 The yttrium oxide powder, the cesium carbonate powder, the sodium carbonate, the rubidium carbonate, the zirconium oxide powder and the lithium oxide powder were mixed with ethanol in the same manner as in the Examples so that the composition had the following 10 chemical formulas. After mixing with a ball mill in a vacuum oven, the powder was calcined in air at 1000 ° C. for 1 h, and the powder was molded into pellets with a hydrostatic pressure of ² t / cm ² . The obtained sample was sintered at 1500 ° C. for 4 hours in air to obtain a sample.

Comparative Example 1: (Y _0.16 Zr _0.82 ) O _1.84 Comparative Example 2: {(Y _0.25 Na _0.75 ) _0.28 Zr _0.72 } O _2-y Comparative Example 3: {(Y _0.5 Na _0.5 ) _0.08 Zr _0.92 } O _1.92 Comparative Example 4: {(Y _0.5 Na _0.5 ) _0.35 Zr _0.65 } O _1.6 Comparative Example 5: {(Y _0.9 Na _0.1 ) _0.28 Zr _0.72 } O _1.83 Comparative Example 6: {(Y _0.5 Cs _0.5 ) _0.05 (Zr _0.67 Li _0.33 ) _0.95 } O
_1.48 Comparative Example 7: {(Y _0.5 Cs _0.5 ) _0.35 (Zr _0.45 Rb _0.55 ) _0.65 } O
_2-y Comparative Example 8: {(Y _0.5 Na _0.5 ) _0.2 (Zr _0.4 Rb _0.6 ) _0.8 } O _2-y Comparative Example 9: {(Y _0.2 Na _0.8 ) _0.2 (Zr _0.67 Li _0.33 ) _0.8 } O
_2-y Comparative Example 10: {(Y _0.9 Na _0.1 ) _0.2 (Zr _0.67 Li _0.33 ) _0.8 } O
_1.48 However, the above oxygen number is a value calculated from the balance of positive and negative charges.

The conductivity values at 950 ° C. are also shown in Table 1.

Comparative Example 2, Comparative Example 7, Comparative Example 8 and Comparative Example 9 are not a single phase of fluorspar, Comparative Example 2 is a mixed phase of an extremely small amount of sodium oxide and a fluorspar compound, and Comparative Example 7 is cesium oxide. The mixed phase of the fluorite compound, Comparative Example 8 was a mixed phase of rubidium oxide and the fluorite compound, and Comparative Example 9 was a mixed phase state of an extremely small amount of sodium oxide and the fluorite compound. Therefore, since Comparative Examples 2, 7, 8 and 9 are not single phase,
Since the oxygen number is unclear, it is described above.
In Comparative Examples 3 and 6, a tetragonal zirconia phase coexisted in addition to the cubic fluorite structure, and it is considered that the ionic conductivity was lowered for this reason.

[0032]

INDUSTRIAL APPLICABILITY As described above, the present invention relates to a fluorite-type ZrO ₂ type solid electrolyte having a large amount of oxygen defects, and it is possible to obtain a new solid electrolyte utilizing the function of this oxygen defect. Becomes

Claims (2)

[Claims] 1. A following general formula _{(1) {(Y 1-} a M a) x Zr 1-x} O 2-y (1) ( wherein, M represents a monovalent alkali metal or Mg or Ba
Where a, x and y are 0.30 <a <0.67, 0.
Represents a real number that satisfies 12 <x <0.35 and 0.078 <y <0.41. ) Fluorite type solid electrolyte represented by. Wherein the following formula _{(2) {(Y 1-} a M a) x (Zr 1-b N b) 1-x} O 2-y (2) ( wherein, M, N is a monovalent Alkali metal or Mg or Ba, M ≠ N, a, x, b and y are 0.30 <a
<0.67, 0.16 <x <0.27, 0 <b <0.5
And a real number satisfying 0.18 <y <0.87. ) Fluorite type solid electrolyte represented by.