High-pressure and high-temperature X-ray diffraction studies of scheelite BaWO4

We carried out high-pressure (HP) and high-temperature (HT) in situ ADXRD synchrotron measurements in barium tungstate (BaWO4) up to 7.5GPa and 800K. Coexistence of the scheelite and fergusonite structures was found beyond 7GPa, both at room temperature and HT, suggesting a polymorphism zone in the P-T phase diagram. The experiments are complemented by thermodynamic calculations within the quasi-harmonic approximation. At ambient pressure, a volume thermal expansivity of 9.510-6K-1 was obtained for scheelite BaWO4. At HP, the thermal expansivity of the fergusonite doubles that of scheelite. Theoretical equation of state curves at HP and HT are also presented.