Synchrotron X-Ray Powder Diffraction Studies of Structural Phase Transitions in Perovskite Oxides

The utilization of the high resolution powder diffractometer at the Australian Synchrotron to obtain accurate and precise structures of some perovskite-type oxides is described. The structure of CdTiO3 has been studied from room temperature to 1000 degrees C by high-resolution synchrotron X-ray powder diffraction. It was found that CdTiO3 remains orthorhombic in the Pbnm space group over the entire temperature range, with the expansion in the cell volume well fitted to the expression Vol = 219: 355(6) + 0: 00818(1)T. The magnitudes of the TiO6 tilts are estimated from the refined structural parameters and these progressively reduce as the temperature is increased. The effect of Sr content on the room temperature structure of the double perovskites Ba2-xSrxInTaO6 is also described. At room temperature Ba2InTaO6 crystallizes in a cubic structure in space group Fm (3) over barm. Doping with Sr results in tilting of the corner sharing octahedra with a concurrent lowering of symmetry with the sequence of structures being Fm (3) over barm(a(0)a(0)a(0)) x similar to 0.6 -> 14/m(a(0)a(0)c(-)) x similar to 1.2 -> I2/m(a(0)b(-)b(-)) x similar to 1.8 -> P2(1)/n(a(-)a(-)c(+))