Synthesis and structural characterization of five layer copper titanium oxide perovskites

The synthesis and characterization of six members of the ordered quintuple copper titanium perovskite series LnBaCaCuTiO are reported. Structural characterization, carried out by a combination of powder X-ray and powder neutron diffraction and EXAFS, shows full ordering of the cations for Ln = Sm, Eu, Gd in the tetragonal space group P4/mmm with the B type cations stacked in the order Cu-Ti-Ti-Ti-Cu. For Ln = Nd partial disorder on both the A and B cation sublattices occurs and oxygen is incorporated between the CuO layers. In LaBaCaCuTiO there is full disordering on both the A and B cation lattices leading to a simple cubic unit cell. When Ln = Tb and Dy, the symmetry of the structure is reduced to an orthorhombic cell, though the B cation stacking is maintained. In all materials the TiO octahedra are distorted. The in-plane Cu-O distances are similar to those found in high-temperature superconductors and are significantly shorter than those found in the corresponding quadruple copper titanium lanthanide perovskites.