Synthesis and properties of LnBaFeCoO5 + δ (Ln = Nd, Sm, Gd)

Abstract

LnBaFeCoO5 + δ (Ln = Nd, Sm, Gd) layered oxides have been synthesized and their crystal structure, thermal stability, thermal expansion, electrical conductivity, thermoelectric power, and magnetic susceptibility have been studied. The oxides have a tetragonal structure (sp. gr. P4/mmm) with unit-cell parameters a = 0.3909(2) nm and c = 0.7695(6) nm for Ln = Nd (δ = 0.65), a = 0.3908(3) nm and c = 0.7662(6) nm for Ln = Sm (δ = 0.37), and a = 0.3908(2) nm and c = 0.7613(6) nm for Ln = Gd (δ = 0.37). The LnBaFeCoO5 + δ compounds are antiferromagnetic p-type semiconductors. With decreasing Ln3+ ionic radius, their electrical conductivity and linear thermal expansion coefficient decrease and their thermoelectric power and antiferromagnetic ordering temperature increase. Near 518–653 K, the linear thermal expansion coefficient of the LnBaFeCoO5 + δ oxides increases from (12.9–16.6) × 10−6 to (19.3–26.5) × 10−6 K−1, which is due to the release of weakly bound oxygen from the oxides. We have determined parameters of charge transport in the [Fe(Co)O2] layers in the crystal structure of the LnBaFeCoO5 + δ phases.