High-temperature monoclinic α-SrHfF, and isostructural α-SrZrF: associating HfF bipolyhedra and SrF snub disphenoids.

The structure of the high-temperature monoclinic variety α-SrHfF (strontium hafnium hexafluoride) [and of isostructural α-SrZrF (strontium zirconium hexafluoride)] associates HfF bipolyhedra and SrF snub disphenoids, forming zigzag twisted [SrF] layers. The distribution of the Hf and Sr polyhedra forms a three-dimensional framework which can be related to the family of anion-excess ReO-related superstructures. α-SrHfF corresponds to a new ABX type and is compared to the other main families already described.

High-temperature elastic moduli of flux-grown α-GeO2 single crystal.

From high-precision Brillouin spectroscopy measurements, six elastic constants (C11, C33, C44, C66, C12, and C14) of a flux-grown GeO2 single crystal with the α-quartz-like structure are obtained in the 298-1273 K temperature range. High-temperature powder X-ray diffraction data is collected to determine the temperature dependence of the lattice parameters and the volume thermal expansion coefficients. The temperature dependence of the mass density, ρ, is evaluated and used to estimate the thermal dependence of its refractive indices (ordinary and extraordinary), according to the Lorentz-Lorenz equation.