Preparation and characterization of Sr2 –xLaxFeO4(0 ⩽x⩽ 1)

Abstract

Solid-solution Sr_{2 –x}La_xFeO₄ crystallizing in the K₂NiF₄ structure has been obtained for 0 ⩽x⩽ 1. In the Sr-rich region, the K₂NiF₄ structure was stable only at low temperature. Heat treatment under an oxygen pressure of 100-500 atm was carried out to form oxygen stoichiometric samples. The structure was refined by the Rietveld method assuming space group I4/mmm. The FeO₆ octahedron in Sr₂FeO₄ showed almost cubic symmetry, the La substitution causing an increase in the Fe–O (apical) length without modifying the a-axis length. All the samples showed semiconducting behaviour and positive Seebeck coefficients. An antiferromagnetic transition at 60 K was observed for Sr₂FeO₄, becoming obscure with increasing La content. The room-temperature Mössbauer spectra showed a symmetric singlet due to Fe⁴⁺ and a doublet due to Fe₃₊, except for Sr₂FeO₄ which showed a quadrupole doublet.