Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O{sub 3-y} perovskites - perspective cathode materials for IT-SOFC
- Department of Chemistry, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation)
- Department of Physics, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation)
- Department of Materials and Environmental Chemistry, Stockholm University, Stockholm S-10691 (Sweden)
- EMAT, University of Antwerp, Groenenborgerlaan, Antwerp 171, B-2020 (Belgium)
Oxygen deficient perovskites Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75, were prepared by using the citrate route at 1373-1573 K for 48 h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a={radical}(2) Multiplication-Sign a{sub per}, b=2 Multiplication-Sign a{sub per}, c={radical}(2) Multiplication-Sign a{sub per} (a{sup 0}b{sup -}b{sup -} tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}x{<=}0.6 and compound Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92} were prepared in air at 1573 K for 48 h. The crystal structure of Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92} was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4) A, R{sub p}=0.057, R{sub wp}=0.056, {chi}{sup 2}=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298-1073 K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5, 0.75 and Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92(1)} are 15.5, 15.1, and 13.8 ppm K{sup -1}, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr{sub 0.15}Ca{sub 0.6}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y} and Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92}. Conductivity of Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75 increases with the temperature reaching 110 S/cm for x=0.5 and 44 S/cm for x=0.75 at 1173 K. Samples of Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}y{<=}0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the {sigma} value from {approx}1 to {approx}50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (E{sub p}) increasing from 340 to 430 meV with an increase of the calcium content from x=0 to x=0.6. - Graphical abstract: The substitution of cobalt in the 314-phase Sr{sub 0.75}Y{sub 0.25}CoO{sub 2.62} by manganese leads to the formation of oxygen deficient compounds Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75, with the cubic and orthorhombic perovskite structures. The conductivity of the x=0.5 sample (110 S/cm) at 1173 K is substantially higher in comparison with x=0.75 (44 S/cm). Together with comparable TEC values for x=0.5 (15.5 ppm K{sup -1}) and 0.75 (15.1 ppm K{sup -1}) samples this makes the former one a promising cathode material for IT-SOFC. Partial replacement of Sr by Ca in Sr{sub 0.75}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y} leads to the formation of the solid solution with the orthorhombic perovskite structure, Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}y{<=}0.6. Along with Sr{sub 0.75}Y{sub 0.25}Co{sub 0.5}Mn{sub 0.5}O{sub 3-y}, novel perovskite Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} represent promising cathode material for IT-SOFC due to low TEC value (13.8 ppm K{sup -1}) and high conductivity of 135 S/cm at 1173 K. Highlights: Black-Right-Pointing-Pointer Mn-doped 314-phases Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5, 0.75 were synthesized. Black-Right-Pointing-Pointer Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, x=0.1--0.6, Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} were made. Black-Right-Pointing-Pointer High-temperature conductivity properties and crystal structure were studied. Black-Right-Pointing-Pointer High-temperature thermal expansion behavior was investigated.
- OSTI ID:
- 22131121
- Journal Information:
- Journal of Solid State Chemistry, Vol. 192; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACTIVATION ENERGY
ANISOTROPY
CATHODES
DOPED MATERIALS
NEUTRON DIFFRACTION
N-TYPE CONDUCTORS
ORTHORHOMBIC LATTICES
OXYGEN
PEROVSKITE
SOLID OXIDE FUEL CELLS
SOLID SOLUTIONS
SPACE GROUPS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0400-1000 K
TETRAGONAL LATTICES
THERMAL EXPANSION
X-RAY DIFFRACTION