Thermal structural properties of calcium tungstate

The results of in situ temperature-resolved powder diffraction studies of CaWO₄ scheelite using both synchrotron radiation and neutron scattering are reported. The studies performed over a broad temperature range of 5-1773 K confirm the scheelite type of structure for calcium tungstate over the whole temperature range. The anisotropy of thermal expansion in calcium tungstate as well as the rigidity of WO₄ complexes have been analysed in terms of bond distances, interatomic angles and anisotropic displacement parameters. The WO₄^2- complex anions showed a remarkable robustness in the whole studied temperature range, thus pointing out that the layered structure formed by two-dimensional CsCl-type arrangements of Ca cations and WO₄ complexes is the primary reason for the anisotropy of thermal expansion in calcium tungstate.