Structural, elastic and vibrational properties of celestite, $SrSO_4$, from synchrotron x-ray diffraction, thermal diffuse scattering and Raman scattering

In order to resolve inconsistencies encountered in published data for SrSO$_4$, the elasticity and the phase stability of celestite has been studied using thermal diffuse scattering, high pressure powder synchrotron x­ray diffraction, Raman scattering and DFT calculations. The structure of SrSO$_4$ is found to be stable up to 62 GPa at ambient temperature. The preferred values for the components of the elastic stiffness tensor have been determined using x­ray thermal diffuse scattering and are (in GPa): $c_{11} = 105, c_{22} = 92, c_{33} = 114, c_{44} = 16, c_{55} = 31, c_{66} = 26, c_{12} = 40, c_{13} = 52, c_{23} = 37$. The preferred value for the bulk modulus is K=62(2)GPa. This work shows that thermal diffuse scattering collected at two temperatures allows the determination of the full elastic tensor of crystals with low space group symmetry