The novel phase transition of NaBi(WO4)2 under high pressure

The Raman and synchrotron angle-dispersive X-ray diffraction studies have been performed on NaBi(WO4)2 under high pressure up to 30.7 and 36.2 GPa, respectively, at room temperature. With pressure increases to ∼7.0 GPa, the structure of NaBi(WO4)2 begins to transform from tetragonal (I41/a) into monoclinic (P2/m), and the phase transition completes around 13 GPa. With pressure higher than 29.0 GPa, the NaBi(WO4)2 turns into amorphous state. The random arrangement of Na+ and Bi3+ in short-range ordered scheelite NaBi(WO4)2 results in the tetragonal to monoclinic phase transition, which is different from that observed in AWO4 tungstates and AMoO4 molybdates (A=Ca, Sr, Ba, Pb, Eu, Cd).