Structural studies of layered cuprates and bismuthates

Abstract

Studies have been undertaken trying to produce new high Tc, superconducting cuprates. As a mechanism for superconductivity in these materials is sought, it is important to produce new materials with new structural features. Studies were carried out on three systems: bismuthates, quadruple perovskites and ruthenates. Bismuthate work was aimed at trying to intergrow Sillen type phases with layered cuprate phases. This work yielded four new Sillen related structures: CaBiO2Cl [P21/m : a = 7.7311(1)Å, b = 4.1234(1)Å, c = 6.3979(2)Å and ß = 105.21(1)0] has a puckered halide layer due to the lower co-ordination preference of the small Ca2+ ion. SrBiO2C1 [Cmcm : a = 5.7109(2)Å, b = 12.4081(5)Å, c = 5.5888(2)Å] is a Sillen X1 type material with an ordering of Sr and Bi in the double fluorite layers as previously observed in BaBiO2C1. Bi2LaO4C1 [I4/mmm: a = 3.9547(1)Å and c = 9.1275(3)Å] has triple fluorite layers with ordering such that La occupies the central layer only. These layers are separated by planar Cl layers. Isostructural Bi2NdO4C1 and Bi2YO4CI have also been prepared. Bi6Ca5O11Cl6[Cmcm: a = 3.865(6)Å, b = 12.57(2)Å and c = 43.05(7)Å] has an X1 related, Arppe type structure, with undulating (M2O2) layers, determined from microcrystal diffraction data. Microcrystals formed on reaction of the stoichiometry Bi1.7Ca2.7O4-yCl4 were shown to possess a Sillen X1X3 type structure, confirming a previous report. Work on perovskites involved doping studies of the Quadruple Perovskite series Ln2Ba2Cu2Ti2O11 (Ln = Nd, Gd and Tb). Investigation of Sr doping for Ba in this series is reported, as is Cu substitution for Ti in the Nd system. Work on trying to extend the observation of both superconductivity and ferromagnetism in the ruthenate RuSr2GdCu2O8 involved investigation of RuSr2TbCu2O8 1-2-1-2 and quadruple perovskite Ln2Ba2Cu2Ru2O11 (Ln = La, Nd, Gd and Tb) and NdBa3Cu2TiNb1-xRuxO11 systems.