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, image) 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 12–50 K, 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 image–Pbnm phase transition for LaGaO3, CeGaO3 and La1−xRExGaO3 (RE—rare earth) perovskites.