Solid electrolyte, multilayer body, and fuel cell

Abstract

One aspect of the present disclosure provides a solid electrolyte which has a perovskite crystal structure having a mother crystal that is represented by general formula AMaO3-δ and an element Mb for substituting a part of Ma in the mother crystal and forming a solid solution, wherein the mother crystal has a |∇a| / |∇b| value of more than 0 but less than 1.568, where ∇a is the inclination of a graph indicating the relationship between a change in the crystal lattice volume and a substitution solid solution ratio of Mb when Mb is solid-solved in a perovskite crystal represented by AMaO3-δ, and ∇b is the inclination of a graph indicating the relationship between a change in the crystal lattice volume and a substitution solid solution ratio of Mb when Mb is solid-solved in a crystal represented by AMaO3 in which δ of the perovskite crystal is filled with an oxygen atom.

Description

Solid electrolyte, laminate, and fuel cell

[0001] The present disclosure relates to a solid electrolyte, a laminate, and a fuel cell.

[0002] Depending on the type of electrolyte, known fuel cells include alkaline electrolyte fuel cells, phosphate fuel cells, solid polymer fuel cells, solid oxide fuel cells, etc. Among these, solid oxide fuel cells are attracting particular attention because they do not use expensive catalysts such as platinum and have high power generation efficiency.

[0003] However, solid oxide fuel cells have not become widespread due to the high operating temperatures of 700 to 1000°C, the need for preheating for operation, and the need for durability in the materials that make up the fuel cell. Therefore, in order to lower the operating temperature, studies are being conducted on the use of oxides with a perovskite structure as the proton-conducting oxide electrolyte. For example, Patent Document 1 discloses a solid electrolyte laminate formed from yttrium-doped barium zirconate.

[0004] Japanese Patent Application Laid-Open No. 2013-206703

[0005] An object of the present disclosure is to provide a solid electrolyte that can exhibit excellent proton diffusion performance in a medium temperature range of about 300 to 400° C. Another object of the present disclosure is to provide a laminate including the above-described solid electrolyte. Another object of the present disclosure is to provide a fuel cell that is excellent in operation in a medium temperature range.

[0006] The diffusion of protons in solid electrolytes is represented by the general formula AMaO ３ It is believed that this occurs by sequential hopping of the electron cloud around the oxygen atom in the perovskite-type crystal represented by the formula: ##EQU1## It is also believed that the proton diffusion performance can be controlled by lowering the energy barrier felt by the proton during this movement. Through investigation, the present inventors have found that one means for lowering the energy barrier is to use an AMaO crystal having oxygen vacancies in the crystal. ３－δ The change in the crystal lattice volume when an additional element (Mb) is dissolved in the perovskite crystal shown in ３The mother crystal is a crystal whose behavior is similar to the change in the crystal lattice volume when Mb is dissolved in the crystal represented by the formula (1), more specifically, AMaO ３－δ and AMaO ３ A perovskite crystal represented by ３－δ and AMaO ３ The present inventors have discovered a new finding that it is important to use a crystal as a host crystal such that, when the ratio of the rate of change in crystal lattice volume (i.e., the slope) in a graph plotting the relationship between the crystal lattice volume and the Mb addition rate, where the vertical axis represents the crystal lattice volume of each crystal and the horizontal axis represents the addition rate of the element Mb, the ratio is less than a predetermined value. Furthermore, the inventors have discovered that the rate of change in the crystal lattice volume when the amount of Mb added is changed shows a similar trend regardless of the presence or absence of oxygen vacancies, which corresponds well to a decrease in the activation energy of proton diffusion and an increase in the proton diffusion coefficient. The present disclosure is based on these new findings. The change in the crystal lattice volume is related to the change in the lattice length of the unit lattice in the perovskite crystal, and the small change in lattice length means that the addition of Mb can absorb environmental changes caused by the addition of Mb without causing a significant change in the unit lattice, and the crystal can be said to have excellent flexibility.

[0007] One aspect of the present disclosure provides the following [1]: [1] General formula: AMaO ３―δ (in the general formula, A represents an A-site element in the perovskite structure, Ma represents a B-site element in the perovskite structure, and δ is a value less than 3), and an element Mb that substitutes for a part of Ma in the mother crystal to form a solid solution, wherein the mother crystal is represented by AMaO ３―δ The graph showing the relationship between the change in crystal lattice volume and the substitutional solid solution ratio of Mb when Mb is dissolved in a perovskite crystal represented by the formula (1) is defined as ∇a, and δ of the perovskite crystal is filled with oxygen atoms. ３The solid electrolyte is a crystal in which the value of |∇a| / |∇b| is greater than 0 and less than 1.568, where ∇b is the slope of a graph showing the relationship between the change in crystal lattice volume when Mb is dissolved in a solid solution and the substitutional solid solution ratio of Mb for a crystal represented by the formula:

[0008] When the host crystal is hard, the value of |∇a| / |∇b| is large, i.e., the addition of Mb significantly changes the energy barrier when protons move. In contrast, the solid electrolyte has a host crystal whose value of |∇a| / |∇b| falls within the predetermined range. A solid electrolyte having such a configuration has a small energy barrier when protons move in a potential field generated by the overlap of electron clouds around oxygen. This allows the solid electrolyte to have excellent proton diffusion performance.

[0009] One aspect of the present disclosure provides the following [2] to [9].

[0010] [2] General formula: A(Ma １－ｙ Mb ｙ ) O ３―δ (y is a value greater than 0 and equal to or less than 1, and δ is a value less than 3). [3] The ionic radius of A is r Ａ The weighted average value based on the abundance ratio of elements of the ionic radii of Ma and Mb is defined as r Ｍ When this is done, (r Ｍ / r Ａ ) + C is 0.24 to 0.54, and C is C = 0.55 × r Ａ [4] The solid electrolyte according to [1] or [2], wherein the crystal lattice volume is 70.678 × 10 －３ nm ３ The above is 85.052 x 10 －３ nm ３ [5] The solid electrolyte according to any one of [1] to [3], wherein the proton conductivity is 1.0 × 10 or less. －３ SCM －１[6] The solid electrolyte according to any one of [1] to [4], wherein A is at least one selected from the group consisting of Ba, Sr, Ca, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Li, Na, K, Rb, Cs, and Mg, and Ma and Mb are each at least one selected from the group consisting of Ti, Zr, Hf, Sn, Pb, Bi, Si, Ge, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, In, Sc, V, Nb, Ta, Cr, Mo, W, Sb, Mg, Al, As, and Re. [7] The solid electrolyte according to any one of [1] to [5], wherein A is at least one selected from the group consisting of Ba, Sr, Ca, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, In, Sc, V, Nb, Ta, Cr, Mo, W, Sb, Mg, Al, As, and Re. １－ｙ Sc ｙ O ３－δ (wherein y is a value of 0.2 to 0.7, and δ is a value of 0.2 to 3), and the general formula: BaTi １－ｙ Sc ｙ O ３－δ (wherein y is a value of 0.2 to 0.8 and δ is a value of 0 to 3), or a compound represented by the general formula: BaTi １－ｙ－ｘ Sn ｙ Sc ｘ O ３－δ (where y is a value of 0.05 to 0.15, x is a value of 0.2 to 0.8, and δ is a value of 0 to 3). [8] A stack comprising a first electrode, an electrolyte membrane provided on the first electrode, and a second electrode provided on the side of the electrolyte membrane opposite to the first electrode side, wherein the electrolyte membrane comprises the solid electrolyte according to any one of claims 1 to 7. [9] A fuel cell comprising the stack according to [8].

[0011] According to the present disclosure, a solid electrolyte capable of exhibiting excellent proton diffusion performance in a medium temperature range of about 300 to 400° C. can be provided. According to the present disclosure, a laminate including the above-described solid electrolyte can also be provided. According to the present disclosure, a fuel cell with excellent operation in a medium temperature range can also be provided.

[0012] FIG. 1 is a graph showing the relationship between the scandium addition ratio and the crystal lattice volume for various perovskite crystals. FIG. 2 is a graph showing the relationship between the proton diffusion coefficient and the activation energy for proton diffusion for the solid oxides prepared in the Examples and Comparative Examples and the scandium addition ratio. FIG. 3 is a graph showing the relationship between the proton conductivity of the solid oxides prepared in the Examples and Comparative Examples and the ∇a / ∇b ratio of the host crystals constituting the various solid oxides. FIG. 4 is a graph showing the results of measuring the proton conductivity for the solid electrolyte prepared in Example 1. FIG. 5 is a graph showing the results of evaluating the chemical stability of the solid electrolyte of Example 1. FIG. 6 is a graph showing the results of measuring the proton diffusion coefficient for the solid electrolyte of Example 1. FIG. 7 is a graph showing the results of evaluating the performance of the solid electrolyte of Example 1 as a solar cell electrolyte. FIG. 8 is a graph showing the results of evaluating the solid electrolyte of Example 3.

[0013] Hereinafter, embodiments of the present disclosure will be described, occasionally with reference to the drawings. However, the following embodiments are merely examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following content. Positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. The dimensional ratios of each element are not limited to those shown in the drawings.

[0014] Unless otherwise specified, the materials exemplified in this specification can be used singly or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. Furthermore, in this specification, numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0015] One embodiment of the solid electrolyte has the general formula: AMaO ３―δand an element Mb that substitutes for a portion of the Ma in the mother crystal. In the general formula, A represents an A-site element in the perovskite structure, Ma represents a B-site element in the perovskite structure, and δ is a value less than 3. In the general formula, A, Ma, and Mb are different elements, and O represents oxygen.

[0016] The mother crystal in the solid electrolyte is AMaO ３―δ The graph shows the relationship between the change in crystal lattice volume and the substitutional solid solution ratio of Mb when Mb is dissolved in a perovskite crystal represented by the formula (1), where ∇a is the slope of the graph, and δ of the perovskite crystal is filled with oxygen atoms. ３ When the gradient of a graph showing the relationship between the change in crystal lattice volume when Mb is dissolved in a solid solution and the substitution solid solution ratio of Mb is ∇b, the value of |∇a| / |∇b| may be greater than 0 and less than 1.568. In the graph, the vertical axis represents the crystal lattice volume (nm ３ ) and the horizontal axis represents the addition ratio of element Mb.

[0017] The upper limit of the value of |∇a| / |∇b| may be, for example, 1.500 or less, 1.300 or less, 1.100 or less, 1.000 or less, or 0.900 or less. When the upper limit of the value of |∇a| / |∇b| is within the above range, the energy barrier experienced by protons during proton conduction can be further reduced, and the proton diffusion performance of the solid electrolyte can be further improved. The lower limit of the value of |∇a| / |∇b| may be, for example, 0.050 or more, 0.100 or more, 0.200 or more, or 0.500 or more. When the lower limit of the value of |∇a| / |∇b| is within the above range, the crystal lattice is more flexible, which further reduces the proton diffusion barrier and further improves the proton diffusion coefficient and proton conductivity.

[0018] With respect to the above-mentioned ∇a and ∇b, the value of ∇a / ∇b of the mother crystal may be, for example, −1 or more and less than 0, or more than 0 and 1 or less, or more than 0 and 1 or less, 0.2 to 1.0, or 0.3 to 1.0.

[0019] The compositions of the solid electrolyte and the mother crystal in this specification can be determined by energy dispersive X-ray analysis (EDS analysis), and the amounts of A, Ma, and Mb dissolved are determined by EDS analysis. The unit cell volume of the crystal to be measured is determined by identifying the lattice constants a, b, and c by powder X-ray diffraction at room temperature and multiplying a, b, and c. The pseudocubic volume (hereinafter also referred to as crystal lattice volume) normalized by the number of perovskite units in the unit cell is derived. The crystal lattice volume obtained as described above is plotted against the amount of Mb dissolved in the corresponding crystal, and a linear approximation graph is created to determine ∇a and ∇b. The lattice constants a, b, and c refer to the lengths of the a-axis, b-axis, and c-axis of the crystal and mother crystal constituting the solid electrolyte, respectively.

[0020] In this specification, when the number of constituent elements of a solid electrolyte is large or the composition formula is unclear, the determination of the above ∇a and ∇b is more specifically performed based on the following method. First, the elements constituting the solid electrolyte and their detected concentrations are determined by energy dispersive X-ray analysis (EDS analysis) of the solid electrolyte. Next, among the detected elements, the element with the highest detected concentration that is a lanthanoid element or an element with a coordination number of 12 as reported in R.D. Shannon, "Revised effective ionic radii and systematic studies of interatomic distance in halides and chalcogenides," Acta Crystallográhica Section A, Volume 32, Issue 5, 1976, pp. 751-767, is defined as the element occupying the A site (A1 element) in the host crystal of the solid electrolyte being measured. Next, the element that is a cationic species with a valence obtained by subtracting the "valence of the A1 element" from "6" and has the highest detected concentration among the detected elements other than the A1 element is taken as the element (Ma1 element) occupying the B site in the mother crystal of the solid electrolyte to be measured. The element that is the highest detected concentration among the detected elements other than the A1 element and the Ma1 element is taken as the element (Mb1 element) substituting a part of the Ma1 element in the mother crystal of the solid electrolyte to be measured. Using the A1, Ma1, and Mb1 elements thus determined, the mother crystal A1Ma1O ３－δ and A1Ma1O ３ The relationship between the crystal lattice volume and the proportion of Mb added when Mb1 is used as an added element is plotted against the above, a linearly approximated straight line graph is created, and the slope is determined to determine ∇a and ∇b for the mother crystal of the solid electrolyte to be measured. Note that in the above method, the valence of the element is the valence shown below. Ba ２＋ , Sr ２＋ , Ca ２＋ , La ３＋ , Ce ４＋ , Pr ３＋ , Nd ３＋ , Sm３＋ , Eu ３＋ , Gd ３＋ , Tb ３＋ , D ｙ３＋ , Ho ３＋ , Er ３＋ , Tm ３＋ , Yb ３＋ , Lu ３＋ , Li １＋ , Na １＋ , K １＋ , Rb １＋ , Cs １＋ , Mg ２＋ , Ti ４＋ , Zr ４＋ , Hf ４＋ , Sn ４＋ , Pb ４＋ , Bi ３＋ or Bi ５＋ , Si ４＋ , Ge ４＋ , Ga ３＋ , La ３＋ , Ce ４＋ , Pr ３＋ , Nd ３＋ , Sm ３＋ , Eu ３＋ , Gd ３＋ , Tb ３＋ , Dy ３＋ , Ho ３＋ , Er ３＋ , Tm ３＋ , Yb ３＋ , Y ３＋ , Lu ３＋ , In ３＋ , Sc ３＋ , V ５＋ , Nb ５＋ , Ta ５＋ , Cr ３＋ , Mo ５＋ or Mo ６＋ , W ５＋ or W ６＋ , Sb ３＋ or Sb ５＋ , Mg ２＋ , Al ３＋ , As ５＋ , Re ６＋

[0021] The mother crystal and the solid electrolyte have a perovskite-type crystal structure, which can be confirmed by X-ray diffraction.

[0022] The solid electrolyte has the general formula: A (Ma １－ｙ Mb ｙ ) O ３―δ (wherein y is a value greater than 0 and equal to or less than 1, and δ is a value less than 3), and may be represented by the general formula: A(Ma １－ｙ Mb ｙ ) O ３―δ (where y is a value of 0.3 or more and 1 or less, and δ is a value of less than 3), and may be represented by the general formula: A(Ma １－ｙ Mb ｙ ) O ３―δ (where y is a value of 0.5 or more and 1 or less, and δ is a value of less than 3). Since protons are introduced into the solid electrolyte during use, the solid electrolyte may be represented by the general formula: A(Ma １－ｙ Mb ｙ ) O ３―δ H ｚ (where y is a value of 0.5 or more and 1 or less, δ is a value less than 3, and z is a value that varies depending on the proton to be introduced).

[0023] The above A includes, for example, at least one selected from the group consisting of Ba, Sr, Ca, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Li, Na, K, Rb, Cs, and Mg, and from the viewpoint of making the crystal lattice volume more appropriate, it may be at least one selected from the group consisting of Cs, Rb, K, Na, Ba, Sr, La, Pr, and Nd, and from the viewpoint of further improving the chemical stability of the obtained solid oxide, it may be at least one selected from the group consisting of Ba, Sr, La, Pr, and Nd.

[0024] The Ma includes at least one selected from the group consisting of, for example, Ti, Zr, Hf, Sn, Pb, Bi, Si, Ge, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, In, Sc, V, Nb, Ta, Cr, Mo, W, Sb, Mg, Al, As, and Re. From the viewpoint of making the crystal lattice volume more appropriate, Ma includes at least one selected from the group consisting of Sn, Ti, Zr, Hf, Pb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, In, Sc, V, Nb, Ta, Cr, Mo, W, Sb, Mg, Al, As, and Re. From the viewpoint of further improving the chemical stability of the obtained solid oxide, the metal oxide may be at least one selected from the group consisting of Ti, Zr, Hf, Sn, Si, Ge, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, In, Sc, V, Nb, Ta, Cr, Sb, Mg, Al, and Re.

[0025] The Mb includes at least one selected from the group consisting of, for example, Ti, Zr, Hf, Sn, Pb, Bi, Si, Ge, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, In, Sc, V, Nb, Ta, Cr, Mo, W, Sb, Mg, Al, As, and Re. From the viewpoint of making the crystal lattice volume more appropriate, Mb includes at least one selected from the group consisting of Sn, Ti, Zr, Hf, Pb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, In, Sc, V, Nb, Ta, Cr, Mo, W, Mg, and R. From the viewpoint of further improving the chemical stability of the obtained solid oxide, it may be at least one selected from the group consisting of Ti, Zr, Hf, Sn, Si, Ge, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, In, Sc, V, Nb, Ta, Cr, Sb, Mg, Al, and Re, and from the viewpoint of increasing the bulk modulus and further improving the flexibility of the crystal lattice, it may be at least one selected from the group consisting of Sc, Ti, Sn, Pb, and In.

[0026] Each of A, Ma, and Mb may contain a plurality of elements as long as they are different from one another.

[0027] More specifically, the solid electrolyte is, for example, a compound represented by the general formula: BaSn １－ｙ Sc ｙ O ３－δ (wherein y is a value of 0.2 to 0.7 and δ is a value of 0.2 to 3), and may be a compound represented by the general formula: BaTi １－ｙ Sc ｙ O ３－δ (wherein y is a value of 0.2 to 0.8 and δ is a value of 0 to 3), or a compound represented by the general formula: BaTi １－ｙ－ｘ Sn ｙ Sc ｘ O ３－δ (wherein y is a value of 0.05 to 0.15, x is a value of 0.2 to 0.8, and δ is a value of 0 to 3) may be used.

[0028] The compositions of the solid electrolyte and the mother crystals herein can be determined by energy dispersive X-ray analysis (EDS analysis). The surface of a dense body of solid electrolyte sintered in dry air is polished to a depth of 100 μm or more with silicon carbide abrasive paper to obtain a surface-finished sample. The surface of the sample is irradiated with an electron beam accelerated at 15 kV, and the resulting characteristic X-ray intensity is observed using a scanning electron microscope (SEM), thereby determining the composition of the solid electrolyte and the mother crystal. The ZAF method is used as a quantitative method. Examples of scanning electron microscopes that can be used include the "SU3500" (product name) manufactured by Hitachi High-Tech Technologies Corporation and the "AZtecEnergy" (product name) manufactured by Oxford Instruments.

[0029] In the solid electrolyte, the ionic radius of A is r Ａ The weighted average value based on the abundance ratio of elements of the ionic radii of Ma and Mb is defined as r Ｍ When this is done, (r Ｍ / r Ａ The value of C = 0.55 × r Ａ It is expressed as -0.89. (rＭ / r Ａ When the value of (r) + C is within the above range, the crystal lattice becomes softer, the proton diffusion barrier is further reduced, and the proton diffusion coefficient and proton conductivity are further improved. Ｍ / r Ａ The lower limit of the value of (r)+C may be, for example, 0.260 or more, 0.300 or more, 0.400 or more, 0.430 or more, 0.437 or more, 0.440 or more, or 0.443 or more. Ｍ / r Ａ When the lower limit of the value of (r) + C is within the above range, the crystal lattice becomes softer, which further reduces the proton diffusion barrier, and the proton diffusion coefficient and proton conductivity are further improved. Ｍ / r Ａ The upper limit of the value of (r) + C may be, for example, 0.500 or less, 0.480 or less, 0.460 or less, 0.458 or less, or 0.456 or less. Ｍ / r Ａ When the lower limit of the value of (a) + C is within the above range, the crystal lattice becomes softer, which further reduces the proton diffusion barrier, and the proton diffusion coefficient and proton conductivity are each further improved.

[0030] The lower limit of the crystal lattice volume of the solid electrolyte is, for example, 70.678 × 10 ―３ nm ３ That's it, 71.965 x 10 ―３ nm ３ That's it, 72.490 x 10 ―３ nm ３ or more, or 73,000 x 10 ―３ nm ３ When the lower limit of the crystal lattice volume is within the above range, the crystal lattice becomes softer, further reducing the proton diffusion barrier, and the proton diffusion coefficient and proton conductivity are further improved. The upper limit of the crystal lattice volume of the solid electrolyte is, for example, 85.052 × 10 ―３ nm ３ The following is 83.000 x 10 ―３ nm ３ Below, 80.000 x 10 ―３ nm ３ The following is 78.000 x 10 ―３ nm３ Below, 75.000 x 10 ―３ nm ３ The following is 73.665 x 10 ―３ nm ３ or 72.417 x 10 ―３ nm ３ When the upper limit of the crystal lattice volume is within the above range, the crystal lattice becomes softer, further reducing the proton diffusion barrier, and further improving the proton diffusion coefficient and proton conductivity. The crystal lattice volume of the solid electrolyte may be adjusted within the above range, for example, 70.678 × 10 －３ nm ３ The above is 85.052 x 10 －３ nm ３ or less, or 70.678 x 10 －３ nm ３ The above is 72.417 x 10 －３ nm ３ The following may be true:

[0031] The above-mentioned solid electrolyte has excellent proton diffusion performance in the medium temperature range of about 300 to 400° C. The lower limit of the proton conductivity of the above-mentioned solid electrolyte at 300 to 400° C. is, for example, 1.0×10 －３ SCM －１ That's it, 2.0 x 10 －３ SCM －１ That's it, 3.0 x 10 －３ SCM －１ or more, or 10 x 10 －３ SCM －１ The upper limit of the proton conductivity of the solid electrolyte at 300 to 400°C is not particularly limited, but is usually 30×10 －３ SCM －１ or less, or 20 x 10 －３ SCM －１ The following is the result.

[0032] The proton conductivity in the intermediate temperature range in this specification can be determined by AC impedance measurement. Specifically, it is determined according to the method described in the Examples of this specification. The proton conductivity is the proton conductivity within the crystal grains, i.e., the proton conductivity in the bulk (σ Ｈ．ｂｕｌｋ) and is expressed as the minimum value in the temperature range of 300 to 400°C.

[0033] The solid electrolytes described above can be prepared by solid-phase synthesis or solution synthesis.

[0034] An example of a method for producing a solid electrolyte includes, for example, a step of pulverizing a raw material mixture containing a compound having A as a constituent element, a compound having Ma as a constituent element, and a compound having Mb as a constituent element to obtain a powder (pulverization step), a step of pressure-molding the pulverized material to obtain a molded product (molding step), and a step of heat-treating the molded product at a temperature of 800 to 1700°C to obtain a sintered body (sintering step). The A, Ma, and Mb each represent different elements, and the descriptions of A, Ma, and Mb described above for the solid electrolyte can be applied. Pressure molding may include, for example, uniaxial pressure molding and cold isotropic compression.

[0035] The compound having A as a constituent element, the compound having Ma as a constituent element, and the compound having Mb as a constituent element may each independently be an oxide, a nitrate, or a carbonate. Examples of the compound having A as a constituent element include barium carbonate and barium nitrate. Examples of the compound having Ma as a constituent element include tin oxide and titanium oxide. Examples of the compound having Mb as a constituent element include scandium oxide and scandium nitrate.

[0036] The sintering step may be carried out, for example, in the atmosphere. The heating temperature in the sintering step may be, for example, 1200 to 1700°C, 1400 to 1700°C, or 1600 to 1700°C. The temperature rise rate in the sintering step may be, for example, 100 to 250°C / hour, 150 to 230°C / hour, or 180 to 200°C / hour.

[0037] The above-described solid electrolyte is useful, for example, as a component of a fuel cell or the like. Specific examples of the component include a laminate in which the above-described solid electrolyte is disposed between electrodes. One embodiment of the laminate includes a first electrode, an electrolyte membrane provided on the first electrode, and a second electrode provided on the side of the electrolyte membrane opposite the first electrode. The electrolyte membrane includes the above-described solid electrolyte.

[0038] The first electrode and the second electrode may be made of the same material or different materials. When the laminate is a component of a fuel cell, for example, the first electrode may be an anode electrode (fuel electrode) and the second electrode may be a cathode electrode (air electrode).

[0039] The material of the anode electrode may be, for example, silver, platinum, palladium, nickel, a mixture of nickel and zirconia-based oxide, a mixture of nickel and ceria-based oxide, or a mixture of nickel and barium zirconate-based oxide.

[0040] The cathode material may be, for example, a perovskite oxide containing silver, platinum, a rare earth element, and a 3d transition metal. Such a perovskite oxide may be, for example, a perovskite oxide represented by the general formula: D1 １－ａ D2 ａ B1 １－ｂ B2 ｂ O ３ (0≦a≦1, 0≦b≦1) can be used. Here, D1 and D2 may be lanthanoids (Ln) such as lanthanum (La), cerium (Ce), praseodymium (Pr), and samarium (Sm), or alkaline earth metals (AE) such as calcium (Ca), strontium (Sr), and barium (Ba). B1 and B2 may be manganese (Mn), iron (Fe), and cobalt (Co). Specific examples of the material for the cathode electrode include Ln １－ａ AE ａ Mn １－ｂ Fe ｂ O ３ , Ln １－ａ AE ａ Mn １－ｂ Co ｂ O３ , and Ln １－ａ AE ａ Co １－ｂ Fe ｂ O ３ , A.E. １－ａ AE ａ Co １－ｂ Fe ｂ O ３ etc.

[0041] The thickness of the first electrode and the second electrode can be adjusted depending on the application of the laminate, etc.

[0042] The thickness of the electrolyte membrane can be adjusted depending on the performance required of the laminate and the application of the laminate. The upper limit of the electrolyte membrane thickness may be, for example, 500 μm or less, 400 μm or less, 300 μm or less, 150 μm or less, 50 μm or less, 25 μm or less, or 15 μm or less. By setting the upper limit of the electrolyte membrane thickness within the above range, proton conductivity can be further improved. The lower limit of the electrolyte membrane thickness may be, for example, 0.1 μm or more, 0.5 μm or more, 1.0 μm or more, 3 μm or more, 5 μm or more, or 10 μm or more. Setting the lower limit of the electrolyte membrane thickness within the above range suppresses a decrease in the mechanical strength of the electrolyte membrane itself and more sufficiently suppresses dielectric breakdown between electrodes. The thickness of the electrolyte membrane can be adjusted within the above range, and may be, for example, 0.1 to 500 μm, 0.1 to 400 μm, 1.0 to 400 μm, 1.0 to 50 μm, or 5 to 15 μm.

[0043] The laminate may include other layers in addition to the first electrode, electrolyte membrane, and second electrode. Examples of the other layers include a layer inserted between the first electrode and the electrolyte, and a layer inserted between the second electrode and the electrolyte. Examples of the layer inserted between the first electrode and the electrolyte include a nickel and barium zirconate-based oxide mixture layer, a nickel and zirconia-based oxide mixture layer, and a nickel and cerium oxide-based oxide mixture layer. Examples of the layer inserted between the second electrode and the electrolyte include a cerium oxide-based oxide, a barium zirconate-based oxide, a cerium-doped barium zirconate-based oxide, and a barium cerate-based oxide.

[0044] The solid oxide fuel cell having the laminate contains the above-mentioned solid oxide as an electrolyte, and therefore can be set at a low operating temperature. The upper limit of the operating temperature of the solid oxide fuel cell can be, for example, 600°C or less, 550°C or less, 500°C or less, 450°C or less, 350°C or less, or 250°C or less. The lower limit of the operating temperature of the solid oxide fuel cell can be, for example, 100°C or more, 200°C or more, 230°C or more, or 300°C or more. The operating temperature of the solid oxide fuel cell can be adjusted within the above-mentioned range, and may be, for example, 250 to 600°C or 100 to 590°C. The solid oxide fuel cell having the laminate also contains the above-mentioned solid oxide as an electrolyte, and therefore can be operated stably for a long period of time (for example, 200 hours or more).

[0045] Although several embodiments have been described above, the present disclosure is not limited to the above embodiments. Furthermore, the descriptions of the above embodiments can be applied to each other.

[0046] The present disclosure will be described in more detail below with reference to examples and comparative examples, although the present disclosure is not limited to the following examples.

[0047] [Selection of host crystal candidates] Barium stannate (BaSnO ３ ), barium titanate (BaTiO ３ ), and barium zirconate (BaZrO ３ ) were prepared, and the unit cell volume and the number of perovskite units in the unit cell were determined by powder X-ray diffraction when a portion of the B-site atoms of the perovskite structure, i.e., Sn, Ti, and Zr, was replaced with scandium (Sc). The crystal lattice volume was determined for each scandium addition ratio while changing the addition ratio. Next, barium stannate (BaSnO) with oxygen vacancies was prepared. ３―δ ), barium titanate (BaTiO ３―δ ), and barium zirconate (BaZrO ３―δ The results are shown in Figure 1. Table 1 also shows the values ​​of ∇a and ∇b, which are the rates of change in the crystal lattice volume corresponding to each graph.

[0048]

[0049] (Example 1) [Ba(Sn ０．３ Sc ０．７ ) O ３―δ Preparation of scandium-doped barium stannate represented by the formula: ３ , manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity: 99.9% by mass, and tin oxide (SnO ２ , manufactured by HIGH PURITY CHEMICALS, purity: 99.9% by mass, and scandium oxide (Sc ２ O ３ (High Purity Chemicals, purity: 99.9% by mass or more) and scandium were weighed out so as to achieve a stoichiometric ratio in accordance with the composition formula of the target scandium-doped barium stannate (composition formula in which y is 0.7 in the general formula), and placed in a mortar together with a predetermined amount of ethanol and wet-mixed. The mixture was heated to 1100°C at a temperature increase rate of 300°C / hour in the atmosphere, and then heat-treated at 1100°C for 5 hours to obtain a calcined powder.

[0050] The calcined powder thus obtained was placed in a container, and a predetermined amount of ethanol and zirconia balls were added thereto. The mixture was then wet-pulverized using a roller mill (NITTO KAGAKU CO., LTD. ANZ-52D) at a rotation speed of 300 rpm for 3 days to obtain a pulverized product. The pulverized product was then dried to obtain a raw material powder.

[0051] The obtained raw material powder was molded into pellets with a diameter of 20 mm and a thickness of approximately 2 mm using a uniaxial pressing machine, and further pressed at 250 MPa using cold isostatic pressing. The pellets were heated to 1600°C while flowing dry air at a flow rate of 100 mL / min, and heat-treated at 1600°C for 12 hours to obtain a sintered body. The heat treatment of the above pellets was carried out in a state where a powder with the same composition as the above raw material powder was prepared and the pellet was covered with this powder in order to prevent the barium component from leaking out of the system and disrupting the composition. The diameter shrank to 13.5 mm upon sintering, and the density of the sintered body was 5.6 g / cm. ３The composition of the obtained sintered body was analyzed by X-ray diffraction (XRD) and confirmed to have a single perovskite structure. The composition of the obtained sintered body was also analyzed by energy dispersive X-ray spectroscopy (EDS) and confirmed to be Ba(Sn ０．３ Sc ０．７ ) O ３―δ It was confirmed that the cation composition was:

[0052] (Example 2) [Ba(Ti ０．２ Sc ０．８ ) O ３―δ Preparation of scandium-doped barium titanate represented by the formula: ２ A calcined powder was obtained in the same manner as in Example 1, except that scandium-doped barium titanate (manufactured by HIGH PURITY CHEMICALS, purity: 99.99% by mass) was used and weighed out to achieve a stoichiometric ratio according to the composition formula of the target scandium-doped barium titanate (composition formula in which y is 0.8 in the general formula). The calcined powder was then placed in a container, a predetermined amount of ethanol and zirconia balls were added, and wet-pulverized for 1 hour at a rotation speed of 300 rpm using a planetary ball mill (manufactured by Fritsch, product name: Planetary Ball Mill Pulverisette 7) to obtain a pulverized product. The pulverized product was dried to obtain a raw material powder. The obtained raw material powder was molded into pellets with a diameter of 20 mm and a thickness of approximately 2 mm using a uniaxial pressing machine and further pressed at 250 MPa using a cold isostatic pressing method. The pellet was heated to 1600°C while dry air was flowing at a rate of 100 mL / min, and then heat-treated at 1600°C for 24 hours to obtain a sintered body. The heat treatment of the pellet was carried out in a state where the pellet was covered with the powder, as in Example 1. The diameter of the sintered body was shrunk to 14.2 mm, and the density of the sintered body was 5.0 g / cm. ３ The composition of the obtained sintered body was analyzed by X-ray diffraction (XRD) and confirmed to have a single perovskite structure. The composition of the obtained sintered body was also analyzed by energy dispersive X-ray spectroscopy (EDS) and confirmed to be Ba (Ti ０．２ Sc ０．８ ) O ３―δ It was confirmed that the cation composition was:

[0053] (Example 3) [Ba(Sn ０．１５ Ti ０．０５ Sc ０．８ ) O ３―δ Preparation of scandium-doped barium tin titanate represented by the formula: ３ , manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity: 99.9% by mass, and tin oxide (SnO ２ , manufactured by HIGH PURITY CHEMICALS, purity: 99.9% by mass, and titanium oxide (TiO ２ , manufactured by HIGH PURITY CHEMICALS, purity: 99.99% by mass, and scandium oxide (Sc ２ O ３, manufactured by HIGH PURITY CHEMICALS, purity: 99.9% by mass or more) and the scandium-doped tin barium titanate were measured out so as to achieve a stoichiometric ratio according to the composition formula of the desired scandium-doped tin barium titanate (composition formula in which y is 0.8 in the general formula). A calcined powder was obtained in the same manner as in Example 1. The calcined powder was then placed in a container, a predetermined amount of ethanol and zirconia balls were added, and the mixture was wet-pulverized for 3 hours at a rotation speed of 300 rpm using a planetary ball mill (manufactured by Fritsch, product name: Planetary Ball Mill Pulverisette 7) to obtain a pulverized product. The pulverized product was then placed in a container, a predetermined amount of ethanol and zirconia balls were added, and the mixture was wet-pulverized for 3 days at a rotation speed of 300 rpm using a roller mill (NITTO KAGAKU CO. LTD. ANZ-52D) to obtain a pulverized product. The pulverized material was dried to obtain a raw material powder. The obtained raw material powder was molded into a pellet having a diameter of 15 mm and a thickness of approximately 2 mm using a uniaxial pressing machine, and further pressed at 300 MPa by cold isostatic pressing. The pellet was heated to 1600°C while flowing dry air at a flow rate of 100 mL / min, and heat-treated at 1600°C for 12 hours to obtain a sintered body. The heat treatment of the above-mentioned pellet was performed in a state where the pellet was covered with the powder, as in Example 1. The composition of the obtained sintered body was analyzed by X-ray diffraction (XRD) and confirmed to have a single perovskite structure. The composition of the obtained sintered body was also analyzed by energy dispersive X-ray spectroscopy (EDS) to determine the presence of Ba(Sn ０．１５ Ti ０．０５ Sc ０．８ ) O ３―δ It was confirmed that the cation composition was:

[0054] (Comparative Example 1) [Ba(Zr ０．４ Sc ０．６） O ３－δ Preparation of scandium-doped barium zirconate represented by the following formula: Barium nitrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Ba(NO ３ ) ２ , purity: 99.9 mass%, and zirconium oxynitrate dihydrate (Kanto Chemical Co., Ltd., ZrO(NO ３ ) ２ ・2H２ O) and scandium nitrate n-hydrate (Kojundo Chemical Laboratory Co., Ltd., Sc(NO ３ ) ３ ・nH ２ Scandium-doped barium zirconate (scandium stearate, purity: 3N) was weighed out so as to achieve a stoichiometric ratio in accordance with the composition formula of the target scandium-doped barium zirconate (composition formula in which x in the general formula is 0.6), and dissolved in approximately 800 mL of distilled water to prepare an aqueous solution. Note that for the hydrates, the amount of hydration was confirmed by thermogravimetric analysis, and then the blending amount was adjusted.

[0055] Ethylenediaminetetraacetic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., EDTA, purity: 99.0% by mass) and citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., purity: 99.0% by mass) were further added to the above aqueous solution so that each amount was 0.5 molar, based on the total number of moles of metal ions in the aqueous solution. The pH of the reaction solution was adjusted to 9.0 or higher and 10 or lower with aqueous ammonia to dissolve the added reagents and obtain a reaction solution. Next, the reaction solution was heated for approximately 300 minutes while stirring on a hot stirrer, and the contents were reacted while the solvent was removed from the system. At this time, the surface temperature of the hot stirrer was adjusted to 180°C. The resulting gel-like material was heated in a microwave heating furnace to remove the solvent contained in the gel-like material and obtain a solid.

[0056] The solid obtained as described above was placed in a heating furnace and heated from room temperature at a heating rate of 5°C / min. After reaching 900°C, the solid was calcined for 10 hours to obtain a precursor. The obtained precursor was placed in a container, and a predetermined amount of ethanol and zirconia balls were added. The precursor was then wet-pulverized using a planetary ball mill (manufactured by Fritsch GmbH, product name: Planetary Ball Mill Pulverisette 7) at a rotation speed of 300 rpm for 2 hours to obtain a pulverized product. The pulverized product was then dried. At the end of this pulverization process, it was confirmed by X-ray diffraction that the resulting product was a mixture of scandium-doped barium zirconate, scandium-doped zirconium oxide, and barium carbonate.

[0057] The crushed mixture was molded into pellets with a diameter of 20 mm and a thickness of approximately 2 mm using a uniaxial press, and then pressurized at 300 MPa using cold isostatic pressing. The pellets were heat-treated at 1600°C for 24 hours while flowing dry air at a flow rate of 100 mL / min to obtain a sintered body. The diameter of the sintered body was shrunk to 15 mm, and the density of the sintered body was 5.3 g / cm. ３ The composition of the obtained sintered body was analyzed by X-ray diffraction (XRD) and confirmed to have a single perovskite structure. The composition of the obtained sintered body was also analyzed by energy dispersive X-ray spectroscopy (EDS) and confirmed to be BaZr ０．４ Sc ０．６ O ３―δ It was confirmed that the cation composition was:

[0058] [Proton conductivity of solid electrolyte (σ Ｈ。ｂｕｌｋ ) Measurement] The solid electrolytes prepared in Examples 1 and 2 and Comparative Example 1 were measured for bulk proton conductivity (σ Ｈ。ｂｕｌｋ ) was measured by AC impedance measurement.

[0059] Specifically, first, both sides of the sintered body were polished to a thickness of approximately 500 μm. Next, a silver layer having a thickness of 650 nm was formed on each side of the polished sintered body using a DC sputtering device (manufactured by Sanyu Electronics Co., Ltd., product name: SC-701HMC II), and this was used as a measurement sample.

[0060] A current collector consisting of a silver mesh (manufactured by Nilaco Corporation) and a gold wire with a diameter of 0.1 mm was prepared, and a silver paste (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., product name: TR-3025) was applied to the current collector. The current collector was attached to both polished surfaces of the measurement sample, and the paste was dried in a dryer at a temperature of 55°C. The resulting laminate was heat-treated in a dry argon atmosphere at approximately 800°C for 1 hour to obtain a measurement sample. The measurement sample was connected to an electrochemical measurement cell with an atmosphere controllable via gold wire. The measurement sample was heated to approximately 720°C in a dry argon atmosphere, and as soon as it reached 720°C, the atmosphere was switched to an argon atmosphere with a water vapor pressure of 0.02 atm. Thereafter, the temperature was lowered and a resistance of 0.1 to 10 was measured by an AC impedance method in a temperature range of approximately 600 to 30°C. ６ The proton conductivity was measured by sweeping the frequency from 100 to 150 Hz. Measurements at each temperature were performed by continuously measuring the AC impedance until the resistance value stabilized to a level where it no longer changed. From the measurement results, the proton conductivity (σ) in the bulk at 300°C was Ｈ。ｂｕｌｋ The relationship between ∇a / ∇b and proton conductivity for each host crystal is shown in FIG. 3. For reference, the temperature dependence of proton conductivity measured for the solid electrolyte of Example 1 is shown in FIG. 4.

[0061] [Measurement of proton concentration] The proton concentration of the solid electrolytes prepared in Examples 1 to 3 and Comparative Example 1 was measured by thermogravimetric analysis. Specifically, the sintered body used in the measurement of proton conductivity was pulverized in an agate mortar to obtain a pulverized material. The obtained powder was subjected to a heat treatment at 1000°C for 1 hour in a dry argon atmosphere using a thermogravimetric analyzer (manufactured by Netsch, product name: STA449F3 Jupiter). The atmosphere surrounding the pulverized material was humidified with water vapor to measure the water vapor partial pressure (p Ｈ２Ｏ Protons were introduced into each solid oxide by adjusting the pressure (atmospheric pressure) to 0.02 atm. The atmosphere was switched to a humidified one, and the temperature was maintained until the mass no longer changed and equilibrium was reached. Assuming that oxygen vacancies in each solid oxide were hydrated by water molecules, the proton introduction rate was calculated from the mass increase observed in the above operation.

[0062] Next, the temperature of the sintered body was gradually lowered to about 115°C to obtain the temperature dependence of the proton introduction rate. By gradually lowering the temperature, the proton introduction rate increased, and the proton introduction rate for each solid oxide at about 300°C, i.e., the proton introduction rate of each solid oxide at about 300°C, was obtained by the general formula: AMa １－ｙ Mb ｙ O ３－δ H ｚ For example, for the solid oxide of Example 3, the value of z was determined as follows: ０．１５ Ti ０．０５ Sc ０．８ ) O ３―δ H ｚ For reference, the results for the solid oxides of Examples 2 and 3 are shown in FIG.

[0063] [Measurement of Proton Diffusion Coefficient of Solid Electrolyte and Measurement of Activation Energy for Proton Diffusion] The proton diffusion coefficient and activation energy for proton diffusion were measured for the solid electrolytes prepared in Examples 1 to 3 and Comparative Example 1. Specifically, the proton diffusion coefficient can be determined by dividing the proton concentration from the obtained proton conductivity using the Nernst-Einstein equation. According to the definition of the Arrhenius plot, the activation energy for proton diffusion was determined from the slope of the plot of the proton diffusion coefficient against the reciprocal of the temperature. The results for the solid oxides of Examples 1 and 2 and Comparative Example 1 are shown in FIG. 2. FIG. 2(a) is a graph showing the measurement results of the proton diffusion coefficient, and FIG. 2(b) is a graph showing the measurement results of the activation energy for proton diffusion.

[0064] [Evaluation of Chemical Stability of Solid Electrolyte] The chemical stability of the solid electrolyte prepared in Example 1 was evaluated. Specifically, the water vapor supplied to the measurement sample was replaced with heavy water (D ２ O) and light water (H ２ The proton conductivity was measured continuously for 258 hours while replacing the heavy water with water. The measurement conditions were a water vapor pressure of 0.02 atm and a temperature of 301°C. The proton conductivity when heavy water was supplied was 5.61 × 10 －３ SCM －１When light water was supplied, the proton conductivity was 10.60 × 10 －３ SCM －１ The results are shown in Figure 5.

[0065] As shown in FIG. 5, the solid electrolyte prepared in Example 1 maintained its proton conductivity for at least 258 hours, confirming that the obtained solid electrolyte had excellent chemical stability.

[0066] [Proton diffusion coefficient in the bulk of the solid electrolyte (D Ｈ。ｂｕｌｋ ) Evaluation] The solid electrolyte prepared in Example 1 was evaluated for the proton diffusion coefficient in scandium-doped barium stannate, which was measured by an AC impedance method.

[0067] Specifically, D Ｈ。ｂｕｌｋ = (σ Ｈ。ｂｕｌｋ RT) / (F ２ C Ｈ where R is the gas constant, T is the temperature, F is the Faraday constant, and C is the Ｈ is the proton concentration. The proton diffusion coefficient was calculated by substituting the proton conductivity and proton concentration at each temperature. An Arrhenius plot of the obtained proton diffusion coefficient is shown in Figure 6. For comparison, Figure 6 also shows the results for scandium-doped barium zirconate and yttrium-doped barium zirconate.

[0068] [Evaluation as a Solid Electrolyte for Fuel Cells] The solid electrolyte prepared in Example 1 was evaluated as a solid electrolyte for fuel cells.

[0069] Specifically, first, both sides of the 15 mm diameter pellet-shaped sintered body (solid electrolyte) prepared in Example 1 were polished so that the thickness of the pellet was 0.3 mm (300 μm). After polishing, platinum paste (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., product name: TR-7907) was applied to both polished surfaces of the pellet to form a circle with a diameter of 8 mm, and then fired at 700 ° C. for 2 hours in a dry air atmosphere, and then cooled to 100 ° C. over 100 hours in a humid atmosphere with a relative humidity of 2% RH to form a platinum electrode. In addition, a platinum mesh was placed on the platinum electrode formed as described above so as to be in contact with it, and silver paste (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., product name: TR-3205) was applied. After drying the silver paste, 60 μL of 2 mol% cerium nitrate was dropped onto both electrodes, and then fired at 300 ° C. for 2 hours in a humid atmosphere with a relative humidity of 2% RH. After firing, the electrode surface turned black due to the influence of cerium nitrate. One electrode served as the anode and the other as the cathode. Next, a platinum wire was wrapped around the side of the pellet to serve as a reference electrode. In this way, an evaluation sample was prepared.

[0070] As shown in FIG. 7(a), a circuit incorporating an evaluation sample was prepared. The relationships between cell voltage and power density and current density were measured. Furthermore, the transition of proton conductivity after 100 hours of continuous operation was confirmed. The results are shown in FIG. 7. FIG. 7(b) is a graph showing the relationship between cell voltage and power density and current density. FIG. 7(c) is a graph showing the time dependence of proton conductivity under fuel cell operating conditions. These results confirmed that the solid electrolyte prepared in Example 1 can exert a theoretical open-circuit electromotive force corresponding to the gas atmospheres on the cathode and anode sides. It was also confirmed that stable fuel cell operation was possible for 100 hours.

[0071] [Ba(Sn ０．１５ Ti ０．０５ Sc ０．８ ) O ３―δ The proton diffusion coefficient (D) in the bulk of scandium-doped barium tin titanate is Ｈ。ｂｕｌｋ ) and proton conductivity (σ Ｈ。ｂｕｌｋMeasurement of the proton diffusion coefficient (D) in the bulk of the solid oxide prepared in Example 3 Ｈ。ｂｕｌｋ ) and proton conductivity (σ Ｈ。ｂｕｌｋ The measurement conditions were the same as those for the solid oxide in Example 1. The results are shown in (b) and (c) of FIG. 8. (b) and (c) of FIG. 8 show the Ba(Ti ０．２ Sc ０．８ ) O ３―δ As shown in FIG. 8(c), the measurement results for scandium-doped barium titanate expressed as Ba(Sn ０．１５ Ti ０．０５ Sc ０．８ ) O ３―δ Scandium-doped barium tin titanate, expressed as －３ SCM －１ It was confirmed that the results exceeded the standard and were excellent.

[0072] According to the present disclosure, it is possible to provide a solid electrolyte that can exhibit excellent proton diffusion performance in the medium temperature range of about 300 to 400° C. According to the present disclosure, it is also possible to provide a fuel cell that is excellent in operation in the medium temperature range.

Claims

1. General formula: AMaO ３―δ (in the general formula, A represents an A-site element in the perovskite structure, Ma represents a B-site element in the perovskite structure, and δ is a value less than 3), and an element Mb that substitutes for a part of Ma in the mother crystal to form a solid solution, the mother crystal being represented by: AMaO ３―δ The gradient of the graph showing the relationship between the change in crystal lattice volume and the substitution solid solution ratio of Mb when Mb is dissolved in a perovskite crystal represented by the formula (1) is ∇a, and δ of the perovskite crystal is filled with oxygen atoms, AMaO ３ wherein, for a crystal represented by the formula (I) above, when the gradient of a graph showing the relationship between the change in crystal lattice volume when Mb is dissolved in solid solution and the substitution solid solution ratio of Mb is ∇b, the value of |∇a| / |∇b| is greater than 0 and less than 1.

568.

2. The ionic radius of A is r Ａ The weighted average value based on the abundance ratio of the elements of the ionic radii of Ma and Mb is r Ｍ Then, (r Ｍ / r Ａ ) + C is 0.24 to 0.54, and C is C = 0.55 × r Ａ The solid electrolyte according to claim 1, wherein the solid electrolyte has a viscosity of -0.

89.

3. The crystal lattice volume is 70.678 x 10 －３ nm ３ Above 85.052 x 10 －３ nm ３ 3. The solid electrolyte according to claim 1 or 2, wherein:

4. Proton conductivity is 1.0 x 10 －３ S.C.M. －１ The solid electrolyte according to claim 1 or 2.

5. The solid electrolyte according to claim 1 or 2, wherein A is at least one selected from the group consisting of Ba, Sr, Ca, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Li, Na, K, Rb, Cs, and Mg, and Ma and Mb are each at least one selected from the group consisting of Ti, Zr, Hf, Sn, Pb, Bi, Si, Ge, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, Lu, In, Sc, V, Nb, Ta, Cr, Mo, W, Sb, Mg, Al, As, and Re.

6. General formula: BaSn １－ｙ S.C. ｙ O ３－δ (y is a value of 0.2 to 0.7, and δ is a value of 0.2 to 3), general formula: BaTi １－ｙ S.C. ｙ O ３－δ (wherein y is a value between 0.2 and 0.8, and δ is a value between 0 and 3), or a compound represented by the general formula: BaTi １－ｙ－ｘ Sn ｙ S.C. ｘ O ３－δ (wherein y is a value of 0.05 to 0.15, x is a value of 0.2 to 0.8, and δ is a value of 0 to 3).

7. A laminate comprising a first electrode, an electrolyte membrane provided on the first electrode, and a second electrode provided on the side of the electrolyte membrane opposite to the first electrode, wherein the electrolyte membrane contains the solid electrolyte according to claim 1 or 2.

8. A fuel cell comprising the laminate according to claim 7.

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