Pressure-induced structural phase transitions in bismuth tungstate Bi2WO6

The pressure-induced structural phase transitions in bismuth tungstate Bi 2 WO 6 have been studied using neutron diffraction and Raman spectroscopy at high pressures up to 7 and 30 GPa, respectively. A rich structural polymorphism was revealed. At P ≃ 3.5 GPa a phase transition from the initial orthorhombic phase of P 2 1 ab symmetry to an orthorhombic phase of B 2 cb symmetry was observed. This transition is caused by the complex spatial rotation of the WO 6 octahedra. A subsequent isostructural phase transition to another orthorhombic phase of B 2 cb symmetry was detected at P ≃ 5.9 GPa, accompanied by changes in both the mutual rotation and tilting of the oxygen octahedra with respect to the crystal b axis. Two more pressure-induced phase transitions in Bi 2 WO 6 at high pressures of 11.5 and 20 GPa were observed in the Raman spectra. These pressure-driven phase transitions in bismuth tungstate are accompanied by anomalies in the pressure dependences of the unit-cell parameters, bond lengths and angles, and in the vibrational modes.