STRUCTURE AND ELECTRICAL-PROPERTIES OF LA1-XSRXCO1-YFEYO3 .2. THE SYSTEM LA1-XSRXCO0.2FE0.8O3

Crystal structure, thermal expansion, oxygen stoichiometry, thermoelec tricity, and electrical conductivity of compositions in the system La1 -xSrxCo0.2Fe0.8O3 with 0 less than or equal to x less than or equal to 0.6 were studied as function of temperature and Sr content, in air. T he solubility of Sr in the sintered perovskite-type oxide (ABO(3)) was limited to x less than or equal to 0.4. The observed p-type electrica l conduction appeared to occur via a small-polaron hopping mechanism. The thermally-induced oxygen loss caused a lattice expansion plus decr eases in both the carrier concentration and the carrier mobility. A se mi-empirical model was developed which takes into account the thermall y activated disproportionation of Co3+ ions into Co4+ and Co2+ pairs, and the ionic compensation of oxygen vacancies formed at high temperat ures. The concentrations of B-site ions (Co or Fe) in different valenc e states were calculated using this model and experimental data.