CRYSTAL-STRUCTURE, ELECTRICAL AND MAGNETIC-PROPERTIES OF LA1-XSRXCOO3-Y

The crystal structure and properties of La1-xSrxCoO3-y with strontium contents ranging from x = 0.1 to x = 0.7 have been studied. The lattice parameters were measured as a function of temperature (4.2-400 K) and the crystal structure was found to change from rhombohedral (at low temperatures and values of x) to cubic. While LaCoO3 is paramagnetic the oxides in the composition range 0.2 < x < 0.6 are soft ferromagnets. The strontium additions are compensated by the formation of Co4+ (cobalt ions with one positive effective charge, Co-Co(.)) and oxygen vacancies (V-O(..)). From the results it is concluded that the relative importance of oxygen vacancies increases with increasing temperature and decreasing oxygen activity. As a result the concentration of electronic charge carriers - and the resultant electrical conductivity - decrease with increasing temperature. The defect structure is discussed and it is concluded that defect associations - probably between oxygen vacancies and strontium ions - and formation of microdomains of perovskite-related phases are important aspects of the overall structure of these perovskite phases.