The effects of substitution of alkaline earths or Y for La on structure and electrical properties of LaSrFeO₄

The effects of the substitution of alkaline earths or Y for La on the structure and electrical properties of LaSrFeO₄ with K₂NiF₄ structure have been investigated. EDTA titration confirmed that Fe³⁺ was oxidized to Fe⁴⁺ in an amount corresponding to that of divalent alkaline earth ions substituted for La³⁺. The change in the lattice constants was interpreted in terms of the ionic radius of the substituted ions and the Jahn-Teller distortion of the Fe(IV)O₆ octahedra having d⁴ electronic configuration. All the substituted LaSrFeO₄ samples were semiconducting over the temperature range from 100 to 300 K. The measurement of the Seebeck coefficient revealed that the conduction carriers of LaSrFeO₄ were holes and the carrier concentration increased with increasing amount of Fe⁴⁺. La_1-xA_xSrFeO₄ exhibited a monotonic decrease in resistivity and activation energy for conduction with increasing Fe⁴⁺ abundance. The activation energy for conduction did not change by changing the lattice constant where the Fe⁴⁺ abundance did not change with various substituents.