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

Perovskite-related materials of composition LaFe1-xCoxO3 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 Fe-57 Mossbauer 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 1200degreesC. In materials where x greater than or equal to ca.0.5 the reduction of Co3+ to Co-0 precedes complete reduction of Fe3+ and the segregation of alloy and metal phases is accompanied by destruction of the perovskite structure. (C) 2004 Elsevier Inc. All rights reserved.