PREPARATION AND CHARACTERIZATION OF SR2-XLAXFEO4 (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1)

Solid-solution Sr2-xLaxFeO4 crystallizing in the K2NiF4 structure has been obtained for 0 less than or equal to x less than or equal to 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 14/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 Mossbauer spectra showed a symmetric singlet due to Fe4+ and a doublet due to Fe3+, except for Sr2FeO4 which showed a quadrupole doublet.