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

Abstract

We carried out high-pressure (HP) and high-temperature (HT) in situ ADXRD synchrotron measurements in barium tungstate (BaWO₄) up to 7.5 GPa and 800 K. Coexistence of the scheelite and fergusonite structures was found beyond 7 GPa, 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 9.5×10⁻⁶ K⁻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.

Keywords:

• scheelite
• fergusonite
• high pressure
• high temperature
• X-ray diffraction
• EOS

Acknowledgements

The authors thank S. Klotz and G. Hamel for their help in the X-ray diffraction measurements. The experiments have been carried out during beamtime allocated to proposal HS-2532 at ID27, ESRF. This study was supported by the MCYT of Spain (grants MAT2007-65990-C03-01 and CSD2007-00045), and the French “Réseau Hautes Pressions” and “Mission Ressources et Compétences Technologiques” of the CNRS. R. Lacomba thanks the support from the MCYT through the “FPU” program.

Additional information

Notes on contributors

D. Errandonea

Currently at the Fundación General de la Universidad de Valencia.