X-ray diffraction study Of WO3 at high pressure

The, high-pressure behaviour of microcrystalline tungsten oxide (WO3) has been investigated with angle-dispersive synchrotron x-ray powder diffraction in a diamond anvil cell up to 40 GPa at room temperature. Up to 21 GPa, the pressure dependence of the volume of the monoclinic high-pressure (P2(1)/c) phase is described by a third-order Birch-Murnaghan equation of state with parameters V-0 = 210.9(7) Angstrom(3), K-T = 27(2) GPa and K' = 9.4(5). At 24 GPa, a first-order phase transition occurs with an approximate DeltaV of 7.4% to a monoclinic P2(1)/a unit cell with a = 6.1669(8) Angstrom, b = 4.5758(6) Angstrom, c = 5.3159(6) Angstrom, beta = 101.440(9)degrees. A second transition is observed at pressures higher than 31 GPa with an approximate DeltaV of 12% to a phase described by a third monoclinic unit cell, with a = 10.3633(22) Angstrom, b 3.9065 (8) Angstrom, c = 9.3459(18) Angstrom and beta = 98.539(14)degrees.