Investigation of orthorhombic perovskite La_1-xCa_xFeO_3-y (0 ⩽ x ⩽ 0.50)

Abstract

La(1-x)Ca(x)FeO3-y, compounds (0 less-than-or-equal-to x less-than-or-equal-to 0.50) have been synthesized and investigated by means of X-ray diffraction and Mossbauer spectroscopy. A linear decrease of the lattice constants of the orthorhombic perovskite with increasing x is found and explained as being partially due to the influence of the increasing valence of iron with increasing x on the ion radius of iron and on the cell dimension. The gradual decrease of isomer shift at room temperature with increasing x arises from the gradually increasing average intermediate valence state of iron due likely to electron hopping not necessarily between paired Fe3+ and Fe4+ but among iron ions mixed in any Fe3+/Fe4+ ratio on identical crystal sites. At low temperature, Fe4+ ions disproportionate into Fe3+ and Fe5+ ions.