Crystal structure and thermal expansion of PrGaO3 in the temperature range 12-1253 K

Crystal structure and thermal expansion of PrGaO3 single crystal, obtained by the Czochralsky method, have been investigated by means of single crystal and high-resolution powder diffraction techniques applying synchrotron radiation in a wide temperature range 12-1253 K. It was shown that PrGaO3 adopts an orthorhombically distorted variant of perovskite structure (GdFeO3 type of structure, space group Pbnm, Z = 4) throughout the entire temperature range. Temperature dependence of lattice parameters and respective unit cell volume display anisotropic and nonlinear behavior. Lattice contraction in [010]- and [100]-directions is observed in temperature ranges 12-180 and 12-50K, respectively. In total PrGaO3 exhibits a negative thermal expansion of the volume between 12 and 50 K. A linear increase of the average bond lengths (PrO)(8), (PrO)(9), (PrO)(12), (GaO)(6), as well as the average (OO)(8) distances was observed. However, with the average (PrPr)(6), (PrGa)(8) and (GaGa)(6) cation-cation distances a change of slope occurs at 200-300 K. Over all, with rising temperature a decrease of the deformation is observed for the perovskite type structure. A phase transition from orthorhombic to rhombohedral structure of PrGaO3 around 1855 K is predicted from extrapolation of both the temperature dependencies of the (PrPr)(6/)(GaGa)(6) distance ratio and of the experimental temperatures of the R3c-Pbnm phase transition for LaGaO3, CeGaO3 and La-1-xRExGaO3 (RE-rare earth) perovskites. (C) 2004 Elsevier Inc. All rights reserved.