Synthesis and characterization of the reduction properties of cobalt-substituted lanthanum orthoferrites

Abstract

Perovskite-related materials of composition LaFe 1− x Co x O 3 have been prepared by conventional calcination methods. The temperature programmed reduction profiles indicate that the incorporation of cobalt renders the materials more susceptible to reduction when treated in a flowing mixture of hydrogen and nitrogen. The reduction processes have been examined by 57Fe Mössbauer spectroscopy and Fe K-edge-, Co K-edge- and La L III-edge XANES and EXAFS. The results show that in iron-rich systems the limited reduction of iron and cobalt leads to the segregation of discrete metallic phases without destruction of the perovskite structure at temperatures up to 1200°C. In materials where x⩾ca.0.5 the reduction of Co 3+ to Co 0 precedes complete reduction of Fe 3+ and the segregation of alloy and metal phases is accompanied by destruction of the perovskite structure.