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 lattic e parameters were measured as a function of temperature (4.2-400 K) an d the crystal structure was found to change from rhombohedral (at low temperatures and values of x) to cubic. While LaCoO3 is paramagnetic t he oxides in the composition range 0.2 < x < 0.6 are soft ferromagnets . The strontium additions are compensated by the formation of Co4+ (co balt ions with one positive effective charge, Co-Co(.)) and oxygen vac ancies (V-O(..)). From the results it is concluded that the relative i mportance of oxygen vacancies increases with increasing temperature an d decreasing oxygen activity. As a result the concentration of electro nic charge carriers - and the resultant electrical conductivity - decr ease with increasing temperature. The defect structure is discussed an d it is concluded that defect associations - probably between oxygen v acancies and strontium ions - and formation of microdomains of perovsk ite-related phases are important aspects of the overall structure of t hese perovskite phases.