Studies of structural, magnetic, electrical and thermal properties in layered perovskite cobaltite SrLnCoO4 (Ln = La, Ce, Pr, Nd, Eu, Gd and Tb)

The structural, magnetic, electrical and thermal properties have been investigated in single-layered perovskite compounds of SrLnCoO4 (Ln = La, Ce, Pr, Nd, Eu, Gd and Tb) with a K2NiF4-type structure. The variation of Jahn-Teller distortion of the CoO6 octahedron reflected by two different Co-O bond lengths indicates that all the samples are mostly accommodated in the t2g orbital states keeping intermediate spin configuration. The detailed comparison of the temperature dependence of magnetization, resistivity, thermoelectric power and thermal conductivity suggests that the tolerance factor t plays a very crucial role in transport behaviour. With decreasing A-site rare earth ionic radius rLn3+, the tolerance factor t decreases and the distortion of the CoO6 octahedron enhances, which results in the increased bending of the Co-O-Co bond, the narrowing of the bandwidth and the decrease in the mobility of eg electrons caused by the substitution of smaller Ln3+ ions for a larger Sr2+ ion