Molecular Dynamics Studies On Strontium And Barium Tungstate

Alkaline-earth tungstates exhibit an interesting phase diagram with respect to increasing pressure. We report molecular dynamics simulation studies on pressure driven transformations of the scheelite phase in SrWO(4) and BaWO(4). We have studied the behavior of the tungstates up to 100 GPa. Our calculated equation of state is in very good agreement with reported experimental and first principles calculations. Our calculations reproduce the scheelite to fergusonite transformation in SrWO(4) and BaWO(4) around 10 and 5 GPa respectively. Volume discontinuity is not apparent at this transition. The two tungstates transform to an amorphous phase beyond 45 GPa with significant volume collapse. The pair correlation functions show that there are subtle changes in the arrangement of the AO(8) polyhedra with increasing pressure. But the WO(4) tetrahedra remain unperturbed with increasing pressure until amorphization occurs. Our calculations indicate that SrWO(4) amorphizes at around 50 GPa, which has not been reported experimentally hitherto.