High-temperature phase transitions in SrHfO3

The crystal structure of SrHfO3 has been studied at high temperatures using powder neutron diffraction and the Rietveld method. From 300 K to approximately 670 K the structure of SrHfO3 is orthorhombic (Pnma). By 870 K the material adopts a second orthorhombic structure (Cmcm). The material then undergoes a further phase transition and is tetragonal (I4/mcm) from similar to 1000 to 1353 K. At higher temperatures (>1360 K) the structure is the ideal cubic perovskite (Pm (3) over bar m). The angle of rotation of the oxygen octahedron in the tetragonal phase is taken as the order parameter and its temperature variation is consistent with a second order phase transition. [S0163-1829(99)06229-3].