Phase transitions and amorphization of CaWO4 at high pressure

The structural phase transitions in CaWO4 were studied by in situ energy-dispersive X-ray diffraction in a diamond-anvil-cell under high pressure up to 65 GPa at room temperature. The previously reported phase transition detected by Raman spectroscopy at 10 GPa was observed in our experiments at 12 GPa and the high-pressure phase was characterized. This transition is from the tetragonal scheelite structure (I4(1)/a) of CaWO4 to a monoclinic wolframite-type structure (P2/c) and a small discontinuity in the evolution of the unit-cell volume was detectable during the transformation (DeltaV/V < -1.9%). In addition, we observed that CaWO4 becomes amorphous at pressures exceeding 40 GPa and found that a novel high-pressure phase of CaWO4 can be obtained at 45 GPa after heating to 477 K and quenching to room temperature an amorphous sample.