Reduction properties of perovskite-related rare earth orthoferrites

Abstract

Perovskite-related materials of composition LaFe1-xCoxO3 have been prepared by conventional calcination methods and by mechanical milling methods. The reduction properties in a flowing mixture of hydrogen and nitrogen have been monitored by temperature programmed reduction techniques and the nature of the reduced phases characterised by X-ray powder diffraction, X-ray absorption spectroscopy and 57 Fe Mossbauer spect roscopy. The smaller particle materials made by mechanical milling methods are more susceptible to reduction than their counterparts made by conventional solid state methods. The presence of cobalt enhances the reducibility of iron in the perovskite-related structures. In iron-rich systems more limited reduction of iron and cobalt leads to the segregation of discrete metallic phases without destruction of the perovskite-related structure at temperatures up to 1200 degrees C whereas in cobalt-rich systems the reduction of Fe3+ and Co3+ leads to significant segregation of alloy and metallic phases and is accompanied by destruction of the perovskite-related structure.