Crystal structure, thermal expansion and electrical conductivity of Nd0.7Sr0.3Fe1-xCoxO3 (0≤x≤0.8)

被引:55
作者
Dasgupta, N [1 ]
Krishnamoorthy, R
Jacob, KT
机构
[1] Bharat Heavy Elect Ltd, Ceram Technol Inst, Bangalore 560012, Karnataka, India
[2] Indian Inst Sci, Ctr Mat Res, Bangalore 560012, Karnataka, India
[3] Indian Inst Sci, Dept Met, Bangalore 560012, Karnataka, India
来源
MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY | 2002年 / 90卷 / 03期
关键词
electrical conductivity; thermal expansion; perovskite; cathode; solid oxide fuel cell (SOFC);
D O I
10.1016/S0921-5107(02)00058-2
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
The crystal structure, thermal expansion and electrical conductivity of the solid solution Nd0.7Sr0.3Fe1-xCoxO3 for 0 less than or equal to x less than or equal to 0.8 were investigated. All compositions had the GdFeO3-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction (XRPD). The pseudo-cubic lattice constant decreased continuously with x. The average linear thermal expansion coefficient (TEC) in the temperature range from 573 to 973 K was found to increase with x. The thermal expansion curves for all values of x displayed rapid increase in slope at high temperatures. The electrical conductivity increased with x for the entire temperature range of measurement. The calculated activation energy values indicate that electrical conduction takes place primarily by the small polaron hopping mechanism. The charge compensation for the divalent ion on the A-site is provided by the formation of Fe4+ ions on the B-site (in preference to Co4+ ions) and vacancies on the oxygen sublattice for low values of x. The large increase in the conductivity with x in the range from 0.6 to 0.8 is attributed to the substitution of Fe4+ ions by Co4+ ions. The Fe site has a lower small polaron site energy than Co and hence behaves like a carrier trap, thereby drastically reducing the conductivity. The non-linear behaviour in the dependence of log sigmaT with reciprocal temperature can be attributed to the generation of additional charge carriers with increasing temperature by the charge disproportionation of Co3+ ions. (C) 2002 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:278 / 286
页数:9
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