High pressure investigations of Na0.025WO3: x-ray diffraction and Raman spectroscopy studies.

High pressure x-ray diffraction and Raman spectroscopy studies have been carried out on non-stoichiometric sodium tungsten bronze, Na(0.025)WO(3). The high pressure investigations reveal a phase transition at about 2 GPa by a change of space group symmetry from P2(1)/n to P2(1)/c in the monoclinic cell followed by a second structural transformation to a triclinic lattice around 18 GPa. There are volume changes with these structural transformations, which are driven by rotation and significant distortion of WO(6) octahedra due to the displacement of tungsten and oxygen atoms from their mean positions in the unit cell.