Crystal structure, electrical and magnetic properties of La1 − xSrxCoO3 − y

The crystal structure and properties of La_{1 ? x}Sr_xCoO_{3 ? 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.