High-temperature electrical properties of magnesiowustite Mg1-xFexO and spinel Fe3-x-yMgxCryO4 ceramics
authors Yaremchenko, AA; Kovalevsky, AV; Naumovich, EN; Kharton, VV; Frade, JR
nationality International
journal SOLID STATE IONICS
author keywords Wustite; Magnetite; Spinel; Electrical conductivity; Seebeck coefficient; Thermal expansion
keywords CATION DISTRIBUTION; MAGNESIUM FERRITE; PHASE-STABILITY; POINT-DEFECTS; NONSTOICHIOMETRY DELTA; CONDUCTIVITY; DEPENDENCE; DIFFUSION; EXPANSION; MOSSBAUER
abstract Phase relationships, thermal expansion and electrical properties of Mg1-xFexO (x = 0.1-0.45) cubic solid solutions and Fe3-x-yMgxCryO4 +/-delta (x = 0.7-0.95; y = 0 or 0.5) spinels were studied at 300-1770K in the oxygen partial pressure range from 10 Pa to 21 kPa. Increasing iron content enlarges the spinel phase stability domain at reduced oxygen pressures and elevated temperatures. The total conductivity of the spinel ceramics is predominantly n-type electronic and is essentially p(O-2)-independent within the stability domain. The computer simulations using molecular dynamics technique confirmed that overall level of ion diffusion remains low even at high temperatures close to the melting point. Temperature dependencies of the total conductivity in air exhibit a complex behavior associated with changing the dominant defect-chemistry mechanism from prevailing formation of the interstitial cations above 1370-1470 K to the generation of cation vacancies at lower temperatures, and with kinetically frozen cation redistribution in spinel lattice below 700-800 K. The average thermal expansion coefficients of the spinet ceramics calculated from dilatometric data in air vary in the range (9.6-10.0) x 10(-6) K-1 at 300-500 K and (13.2-16.1) x 10(-6) K-1 at 1050-1370 K. Mg1-xFexO solid solutions undergo partial decomposition on heating under oxidizing and mildly reducing conditions, resulting in the segregation of spinel phase and conductivity decrease. (C) 2010 Elsevier B.V. All rights reserved.
publisher ELSEVIER SCIENCE BV
issn 0167-2738
year published 2011
volume 192
issue 1
beginning page 252
ending page 258
digital object identifier (doi) 10.1016/j.ssi.2010.05.031
web of science category Chemistry, Physical; Physics, Condensed Matter
subject category Chemistry; Physics
unique article identifier WOS:000292848800056
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