High Pressure Phase Transitions in Barium Tungstate

Abstract

Alkaline-earth tungstates exhibit an interesting phase diagram with respect to pressure. BaWO4 is found to undergo a pressure-driven phase transition at 7.1 GPa from tetragonal scheelite structure to monoclinic fergusonite structure. It is observed to become amorphous beyond 45 GPa. In this work, we report molecular dynamics simulation studies on transformations of the scheelite phase in BaWO4 with increasing pressure at ambient temperature. Our calculated equation of state is in very good agreement with reported experimental data and first principles calculations. In our calculations there is no apparent volume discontinuity at the scheelite to fergusonite transformation in BaWO4 around 7.5 GPa. The tungstate transforms to an amorphous phase beyond 35 GPa with discernable volume collapse. The pair correlation functions show that there are subtle changes in the arrangement of the BaO8 polyhedra with increasing pressure. However, the WO4 tetrahedra remain unperturbed with increasing pressure until amorphization occurs.