Influence of B site substituent Ti on the structure and thermophysical properties of A2B2O7-type pyrochlore Gd2Zr2O7

Since the structural integrity of A(2)B(2)O(7)-type pyrochlores relies mostly on the interconnecting BO6 octahedra, Ti4+ was selected to partially substitute Zr4+ in Gd2Zr2O7 in order to distort the pyrochlore structure in order to improve the material's thermophysical properties for potential use as high-temperature thermal insulation. As evidenced by X-ray diffraction and Raman spectroscopy studies, incorporation of Ti4+ simultaneously leads to long-range ordering of the pyrochlore structure as well as local lattice distortion. These two effects have been shown to be competitive in determining the crystal energy of the Gd-2(Zr1-xTix)(2)O-7 series and result in a minimum value of the Young's modulus at x = 0.3 and a maximum value of the coefficient of thermal expansion at x = 0.2. At lower temperatures, the thermal conductivity of Gd2Zr2O7 was significantly reduced by Ti4+ doping, and its composition dependence was accurately modeled by taking into account the phonon scattering by mass and strain fluctuations at the B site. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.