Phase stabilization and structural disorder in Ln(1.85)Th(0.15)CuO(4) (Ln = Pr, Nd, Sm, Eu and Gd)

A systematic FTIR study of thorium-doped electron superconductors (T' struc ture) series is presented in this paper. Even though all Ln(1.85)Th(0.15)Cu O(4) compounds belong to T' structure, due to different sizes of rare earth ionic radii, the structure stabilization is very difficult to achieve sinc e copper-oxygen distance varies for different members of the series. The or igin of disorder is due to the non-matching of Ln-O/Cu-O bonds in T' struct ure. The built-in internal pressure is responsible for the change of CuO po lyhedron (CuO6 octahedra to CuO2 planar) as relaxing mechanism in the forma tion of T' compounds from T-structured compounds. This is well established from the appearance or disappearance of Cu-O vibration peaks in the FTIR sp ectra. (C) 2001 Elsevier Science Ltd. All rights reserved.