High-temperature dynamic octahedral tilting in the ionic conductor Sr11Mo4O23

López, C.A.; Pedregosa, J.C.; Fernández-Díaz, M.T.; Alonso, J.A.

doi:10.1107/S160057671502261X

High-temperature dynamic octahedral tilting in the ionic conductor Sr₁₁Mo₄O₂₃

C. A. López, J. C. Pedregosa, M. T. Fernández-Díaz and J. A. Alonso

This work presents the crystal structure evolution of a novel ionic conductor Sr₁₁Mo₄O₂₃ at high temperature. The formula of this phase can be rewritten as Sr_1.75□_0.25SrMoO_5.75, highlighting the relationship with double perovskites A₂B′B′′O₆. The crystal network contains oxygen-anion and strontium-cation vacancies. The structure is complex; Sr, Mo and O atoms are distributed in four, two and six distinct Wyckoff sites, respectively. It was refined from neutron powder diffraction data collected at 473, 673, 873 and 1073 K. The thermal evolution of crystallographic parameters supports the known reversible process of removal/uptake of O-atom content in the 673–873 K temperature range. Above 873 K, from difference Fourier maps, it was found that the structure exhibits an oxygen delocalization around one of the Mo sites. This delocalization was understood as a dynamical octahedral tilt of the MoO₆ octahedron, yielding an increase in the ionic conductivity at high temperature.

Keywords: Sr₁₁Mo₄O₂₃; high-temperature structure; neutron powder diffraction; ionic conductors; fuel cells.

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Supporting information

	Crystallographic Information File (CIF) https://doi.org/10.1107/S160057671502261X/ks5496sup1.cif Contains datablocks global, Sr11Mo4O23-473K, Sr11Mo4O23-673K, Sr11Mo4O23-873K, Sr11Mo4O23-1073K
	Rietveld powder data file (CIF format) https://doi.org/10.1107/S160057671502261X/ks5496Sr11Mo4O23-473Ksup2.rtv Contains datablock Sr11Mo4O23-473K
	Rietveld powder data file (CIF format) https://doi.org/10.1107/S160057671502261X/ks5496Sr11Mo4O23-673Ksup3.rtv Contains datablock Sr11Mo4O23-673K
	Rietveld powder data file (CIF format) https://doi.org/10.1107/S160057671502261X/ks5496Sr11Mo4O23-873Ksup4.rtv Contains datablock Sr11Mo4O23-873K
	Rietveld powder data file (CIF format) https://doi.org/10.1107/S160057671502261X/ks5496Sr11Mo4O23-1073Ksup5.rtv Contains datablock Sr11Mo4O23-1073K

CCDC references: 1438983; 1438984; 1438985; 1438986

Computing details top

For all compounds, program(s) used to refine structure: FULLPROF.

(Sr11Mo4O23-473K) top

Crystal data top

Mo4O23.12Sr₁₁	V = 2229.74 (17) Å³
M_r = 1717.17	Z = 4
Tetragonal, I4₁/a	Constant Wavelength Neutron Diffraction radiation
Hall symbol: -I 4ad	T = 473 K
a = 11.6416 (4) Å	yellow
c = 16.4524 (9) Å

Data collection top

D2B Institut Laue Langevin diffractometer	2θ_min = −0.103°, 2θ_max = 159.797°, 2θ_step = 0.050°
Radiation source: nuclear reactor

Refinement top

R_p = 3.185	χ² = 12.834
R_wp = 4.373	3199 data points
R_exp = 1.221	55 parameters
R_Bragg = 8.568	0 restraints

Crystal data top

Mo4O23.12Sr₁₁	V = 2229.74 (17) Å³
M_r = 1717.17	Z = 4
Tetragonal, I4₁/a	Constant Wavelength Neutron Diffraction radiation
a = 11.6416 (4) Å	T = 473 K
c = 16.4524 (9) Å

Data collection top

D2B Institut Laue Langevin
diffractometer

2θ_min = −0.103°, 2θ_max = 159.797°, 2θ_step = 0.050°

Refinement top

R_p = 3.185	χ² = 12.834
R_wp = 4.373	3199 data points
R_exp = 1.221	55 parameters
R_Bragg = 8.568	0 restraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Sr1	0.00000	0.25000	0.12500	0.045 (5)*
Sr2	0.50000	0.25000	0.6013 (16)	0.060 (6)*
Sr3	0.2242 (12)	0.9764 (14)	0.8771 (10)	0.033 (2)*
Sr4	0.2117 (11)	0.2377 (13)	0.5293 (10)	0.051 (3)*
Mo1	0.00000	0.00000	0.00000	0.0094 (15)*
Mo2	0.00000	0.00000	0.50000	0.045 (3)*
O1	−0.1149 (12)	−0.1202 (10)	0.0065 (9)	0.032 (4)*
O2	0.1244 (10)	−0.1150 (13)	0.0075 (12)	0.031 (4)*
O3	−0.0035 (10)	0.0204 (15)	0.1165 (8)	0.023 (3)*
O4	0.08400 (13)	0.0803 (10)	0.5946 (9)	0.021 (4)*	0.78 (2)
O5	0.1203 (11)	−0.0832 (10)	0.4934 (9)	0.046 (4)*
O6	−0.0947 (12)	−0.0624 (14)	0.5702 (10)	0.056 (4)*

Geometric parameters (Å, º) top

Mo1—O1	1.939 (13)	Mo2—O4	2.062 (15)
Mo1—O2	1.976 (14)	Mo2—O5	1.706 (13)
Mo1—O3	1.932 (14)	Mo2—O6	1.754 (16)

O1—Mo1—O2	90.8 (3)	O4—Mo2—O5	85.2 (3)
O1—Mo1—O3	91.1 (3)	O4—Mo2—O6	89.4 (3)
O2—Mo1—O3	92.1 (7)	O5—Mo2—O6	108.8 (4)

(Sr11Mo4O23-673K) top

Crystal data top

Mo4O23.16Sr₁₁	V = 2245.16 (17) Å³
M_r = 1718.77	Z = 4
Tetragonal, I4₁/a	Constant Wavelength Neutron Diffraction radiation
Hall symbol: -I 4ad	T = 673 K
a = 11.6696 (4) Å	yellow
c = 16.4869 (9) Å

Data collection top

D2B Institut Laue Langevin diffractometer	2θ_min = −0.058°, 2θ_max = 159.842°, 2θ_step = 0.050°
Radiation source: nuclear reactor

Refinement top

R_p = 2.886	χ² = 9.848
R_wp = 3.894	3199 data points
R_exp = 1.241	55 parameters
R_Bragg = 7.076	0 restraints

Crystal data top

Mo4O23.16Sr₁₁	V = 2245.16 (17) Å³
M_r = 1718.77	Z = 4
Tetragonal, I4₁/a	Constant Wavelength Neutron Diffraction radiation
a = 11.6696 (4) Å	T = 673 K
c = 16.4869 (9) Å

Data collection top

D2B Institut Laue Langevin
diffractometer

2θ_min = −0.058°, 2θ_max = 159.842°, 2θ_step = 0.050°

Refinement top

R_p = 2.886	χ² = 9.848
R_wp = 3.894	3199 data points
R_exp = 1.241	55 parameters
R_Bragg = 7.076	0 restraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Sr1	0.00000	0.25000	0.12500	0.054 (7)*
Sr2	0.50000	0.25000	0.6026 (14)	0.091 (7)*
Sr3	0.2345 (10)	0.9722 (10)	0.8805 (8)	0.039 (3)*
Sr4	0.2201 (10)	0.2330 (12)	0.5338 (8)	0.064 (3)*
Mo1	0.00000	0.00000	0.00000	0.030 (2)*
Mo2	0.00000	0.00000	0.50000	0.030 (2)*
O1	−0.1209 (14)	−0.11140 (12)	0.0014 (8)	0.031 (3)*
O2	0.1125 (12)	−0.1169 (17)	0.0085 (10)	0.038 (5)*
O3	−0.0038 (9)	0.0224 (14)	0.1177 (7)	0.028 (3)*
O4	0.0802 (17)	0.0889 (13)	0.5930 (11)	0.041 (4)*	0.79 (2)
O5	0.1239 (14)	−0.0896 (15)	0.4940 (11)	0.077 (7)*
O6	−0.092 (2)	−0.0762 (3)	0.5650 (14)	0.122 (9)*

Geometric parameters (Å, º) top

Mo1—O1	1.919 (16)	Mo2—O4	2.074 (18)
Mo1—O2	1.898 (18)	Mo2—O5	1.787 (17)
Mo1—O3	1.959 (12)	Mo2—O6	1.76 (3)

O1—Mo1—O2	91.2 (3)	O4—Mo2—O5	88.2 (4)
O1—Mo1—O3	93.5 (3)	O4—Mo2—O6	94.5 (4)
O2—Mo1—O3	92.2 (3)	O5—Mo2—O6	103.4 (4)

(Sr11Mo4O23-873K) top

Crystal data top

Mo4O21.84Sr₁₁	V = 2269.09 (14) Å³
M_r = 1697.01	Z = 4
Tetragonal, I4₁/a	Constant Wavelength Neutron Diffraction radiation
Hall symbol: -I 4ad	T = 873 K
a = 11.7075 (3) Å	yellow
c = 16.5548 (8) Å

Data collection top

D2B Institut Laue Langevin diffractometer	2θ_min = −0.078°, 2θ_max = 159.822°, 2θ_step = 0.050°
Radiation source: nuclear reactor

Refinement top

R_p = 2.831	χ² = 8.528
R_wp = 3.937	3199 data points
R_exp = 1.348	72 parameters
R_Bragg = 11.108	24 restraints

Crystal data top

Mo4O21.84Sr₁₁	V = 2269.09 (14) Å³
M_r = 1697.01	Z = 4
Tetragonal, I4₁/a	Constant Wavelength Neutron Diffraction radiation
a = 11.7075 (3) Å	T = 873 K
c = 16.5548 (8) Å

Data collection top

D2B Institut Laue Langevin
diffractometer

2θ_min = −0.078°, 2θ_max = 159.822°, 2θ_step = 0.050°

Refinement top

R_p = 2.831	χ² = 8.528
R_wp = 3.937	3199 data points
R_exp = 1.348	72 parameters
R_Bragg = 11.108	24 restraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Sr1	0.00000	0.25000	0.12500	0.074 (7)*
Sr2	0.50000	0.25000	0.602 (2)	0.057 (7)*
Sr3	0.2263 (17)	0.980 (2)	0.8731 (11)	0.055 (4)*
Sr4	0.2089 (15)	0.246 (3)	0.5270 (14)	0.070 (2)*
Mo1	0.00000	0.00000	0.00000	0.0272 (17)*
Mo2	0.00000	0.00000	0.50000	0.0340 (19)*
O1	0.877 (2)	0.1465 (16)	0.2531 (13)	0.049 (4)*
O2	0.6434 (12)	0.1262 (15)	0.2464 (11)	0.031 (3)*
O3	0.2631 (19)	0.243 (2)	0.3666 (16)	0.055 (4)*
O4a	−0.0857 (14)	−0.055 (2)	0.4116 (17)	0.03800*	0.30 (2)
O4b	−0.0869 (17)	0.094 (2)	0.425 (3)	0.03800*	0.13 (2)
O4c	0.000 (2)	0.072 (2)	0.4003 (16)	0.03800*	0.30 (1)
O5a	0.132 (3)	−0.094 (3)	0.490 (3)	0.03800*	0.30 (2)
O5b	−0.137 (3)	−0.087 (3)	0.485 (3)	0.03800*	0.30 (2)
O5c	−0.163 (2)	0.005 (4)	0.477 (3)	0.03800*	0.30 (2)
O5d	0.000 (2)	−0.170 (2)	0.500 (2)	0.03800*	0.18 (2)
O6a	0.0869 (17)	0.061 (2)	0.4124 (18)	0.03800*	0.30 (2)
O6b	0.0857 (14)	−0.083 (2)	0.409 (2)	0.03800*	0.22 (2)
O6c	0.000 (2)	−0.1479 (19)	0.435 (2)	0.03800*	0.13 (1)

(Sr11Mo4O23-1073K) top

Crystal data top

Mo4O21.92Sr₁₁	V = 2291.72 (14) Å³
M_r = 1698.29	Z = 4
Tetragonal, I4₁/a	Constant Wavelength Neutron Diffraction radiation
Hall symbol: -I 4ad	T = 1073 K
a = 11.7466 (3) Å	yellow
c = 16.6088 (8) Å

Data collection top

D2B Institut Laue Langevin diffractometer	2θ_min = −0.071°, 2θ_max = 159.829°, 2θ_step = 0.050°
Radiation source: nuclear reactor

Refinement top

R_p = 2.602	χ² = 7.028
R_wp = 3.663	3199 data points
R_exp = 1.382	72 parameters
R_Bragg = 10.721	24 restraints

Crystal data top

Mo4O21.92Sr₁₁	V = 2291.72 (14) Å³
M_r = 1698.29	Z = 4
Tetragonal, I4₁/a	Constant Wavelength Neutron Diffraction radiation
a = 11.7466 (3) Å	T = 1073 K
c = 16.6088 (8) Å

Data collection top

D2B Institut Laue Langevin
diffractometer

2θ_min = −0.071°, 2θ_max = 159.829°, 2θ_step = 0.050°

Refinement top

R_p = 2.602	χ² = 7.028
R_wp = 3.663	3199 data points
R_exp = 1.382	72 parameters
R_Bragg = 10.721	24 restraints

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Sr1	0.00000	0.25000	0.12500	0.081 (7)*
Sr2	0.50000	0.25000	0.6004 (17)	0.057 (6)*
Sr3	0.2274 (19)	0.976 (2)	0.8743 (13)	0.062 (4)*
Sr4	0.2069 (18)	0.246 (3)	0.5281 (16)	0.084 (3)*
Mo1	0.00000	0.00000	0.00000	0.0313 (17)*
Mo2	0.00000	0.00000	0.50000	0.0363 (18)*
O1	0.875 (2)	0.1450 (15)	0.2515 (16)	0.056 (5)*
O2	0.6416 (12)	0.1271 (16)	0.2468 (12)	0.042 (3)*
O3	0.259 (2)	0.2418 (19)	0.3656 (14)	0.059 (4)*
O4a	−0.0837 (13)	−0.047 (2)	0.4109 (15)	0.03800*	0.30 (2)
O4b	−0.0847 (18)	0.101 (2)	0.429 (3)	0.03800*	0.14 (2)
O4c	0.0000 (18)	0.0759 (18)	0.4030 (15)	0.03800*	0.30 (2)
O5a	0.131 (3)	−0.093 (3)	0.488 (3)	0.03800*	0.30 (2)
O5b	−0.142 (2)	−0.080 (3)	0.490 (3)	0.03800*	0.30 (2)
O5c	−0.162 (2)	0.000 (5)	0.477 (3)	0.03800*	0.30 (2)
O5d	0.000 (2)	−0.170 (2)	0.500 (2)	0.03800*	0.15 (1)
O6a	0.0847 (18)	0.060 (2)	0.4125 (19)	0.03800*	0.30 (1)
O6b	0.0837 (13)	−0.081 (2)	0.407 (2)	0.03800*	0.24 (2)
O6c	0.000 (2)	−0.142 (2)	0.4280 (15)	0.03800*	0.15 (1)

Experimental details

	(Sr11Mo4O23-473K)	(Sr11Mo4O23-673K)	(Sr11Mo4O23-873K)	(Sr11Mo4O23-1073K)
Crystal data
Chemical formula	Mo4O23.12Sr₁₁	Mo4O23.16Sr₁₁	Mo4O21.84Sr₁₁	Mo4O21.92Sr₁₁
M_r	1717.17	1718.77	1697.01	1698.29
Crystal system, space group	Tetragonal, I4₁/a	Tetragonal, I4₁/a	Tetragonal, I4₁/a	Tetragonal, I4₁/a
Temperature (K)	473	673	873	1073
a, c (Å)	11.6416 (4), 16.4524 (9)	11.6696 (4), 16.4869 (9)	11.7075 (3), 16.5548 (8)	11.7466 (3), 16.6088 (8)
V (Å³)	2229.74 (17)	2245.16 (17)	2269.09 (14)	2291.72 (14)
Z	4	4	4	4
Radiation type	Constant Wavelength Neutron Diffraction	Constant Wavelength Neutron Diffraction	Constant Wavelength Neutron Diffraction	Constant Wavelength Neutron Diffraction
Specimen shape, size (mm)	?, ? × ? × ?	?, ? × ? × ?	?, ? × ? × ?	?, ? × ? × ?

Data collection
Diffractometer	D2B Institut Laue Langevin	D2B Institut Laue Langevin	D2B Institut Laue Langevin	D2B Institut Laue Langevin
Specimen mounting	?	?	?	?
Data collection mode	?	?	?	?
Scan method	?	?	?	?
2θ values (°)	2θ_min = −0.103 2θ_max = 159.797 2θ_step = 0.050	2θ_min = −0.058 2θ_max = 159.842 2θ_step = 0.050	2θ_min = −0.078 2θ_max = 159.822 2θ_step = 0.050	2θ_min = −0.071 2θ_max = 159.829 2θ_step = 0.050

Refinement
R factors and goodness of fit	R_p = 3.185, R_wp = 4.373, R_exp = 1.221, R_Bragg = 8.568, χ² = 12.834	R_p = 2.886, R_wp = 3.894, R_exp = 1.241, R_Bragg = 7.076, χ² = 9.848	R_p = 2.831, R_wp = 3.937, R_exp = 1.348, R_Bragg = 11.108, χ² = 8.528	R_p = 2.602, R_wp = 3.663, R_exp = 1.382, R_Bragg = 10.721, χ² = 7.028
No. of parameters	55	55	72	72
No. of restraints	0	0	24	24

Computer programs: FULLPROF.

Selected geometric parameters (Å, º) for (Sr11Mo4O23-473K) top

Mo1—O1	1.939 (13)	Mo2—O4	2.062 (15)
Mo1—O2	1.976 (14)	Mo2—O5	1.706 (13)
Mo1—O3	1.932 (14)	Mo2—O6	1.754 (16)

O1—Mo1—O2	90.8 (3)	O4—Mo2—O5	85.2 (3)
O1—Mo1—O3	91.1 (3)	O4—Mo2—O6	89.4 (3)
O2—Mo1—O3	92.1 (7)	O5—Mo2—O6	108.8 (4)

Selected geometric parameters (Å, º) for (Sr11Mo4O23-673K) top

Mo1—O1	1.919 (16)	Mo2—O4	2.074 (18)
Mo1—O2	1.898 (18)	Mo2—O5	1.787 (17)
Mo1—O3	1.959 (12)	Mo2—O6	1.76 (3)

O1—Mo1—O2	91.2 (3)	O4—Mo2—O5	88.2 (4)
O1—Mo1—O3	93.5 (3)	O4—Mo2—O6	94.5 (4)
O2—Mo1—O3	92.2 (3)	O5—Mo2—O6	103.4 (4)

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High-temperature dynamic octahedral tilting in the ionic conductor Sr₁₁Mo₄O₂₃

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