Phase stabilisation and structural disorder in Ln1.85Ce0.15CuO4 (Ln=Pr, Nd, Sm, Eu and Gd)

A systematic FTIR study of electron doped compounds of the T′-series are presented in this paper. Rare-earth substituted phases of composition Ln1.85Ce0.15CuO4 (Ln=Pr, Nd, Sm, Eu and Gd) have been synthesised. Single-phase formation is achieved up to RE=Gd, beyond which T′-structure is not stable. Disorder due to RE doping is exhibited in the FTIR spectra of as-prepared materials. The origin of disorder is due to non-matching of LnO/CuO bonds in the T′-structure. The built-in internal pressure is responsible for the change of CuO polyhedron (CuO6 octahedra to CuO2 planar) as relaxing mechanism in the formation of T′-compounds from T-structured compounds. This is well established from the appearance or disappearance of CuO vibration peaks in the FTIR spectra.