The crystal structure of ${\mathrm{SrHfO}}_3$ has been studied at high temperatures using powder neutron diffraction and the Rietveld method. From 300 K to approximately 670 K the structure of ${\mathrm{SrHfO}}_3$ 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 $\mathrm{}(I4/mcm)\mathrm{}$ from ∼1000 to 1353 K. At higher temperatures (>1360 K) the structure is the ideal cubic perovskite $\left(Pm3\mathrm{}¯m\right).\mathrm{}$ 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.

• Received 12 January 1999

DOI:https://doi.org/10.1103/PhysRevB.60.2972