Transition to a new tetragonal phase of WO₃: crystal structure and distortion parameters

Abstract

At 1100 K a new phase of WO3 with space group P4/ncc, a = 5.2885(5) Åand c = 7.8626(8) Å, was established, and its crystal structure was determined. The previously known tetragonal phase P4/nmm, which is shown to exist only above 1170 K, was also refined with a = 5.3031(4) Åand c = 3.9348(3) Åat 1200 K. The difference between the two perovskite-like structures relates to a tricritical non-ferroic transition characterized by a soft mode at the Z-point of the Brillouin zone, which induces antiphase rotations of the WO6 octahedra about [001]. The oxygen sublattice of the lower tetragonal structure is shown to possess the symmetry of the a0a0c- perovskite tilt structure F4/mmc (I4/mcm), which is violated by the off-centre antiferroelectric displacements of the tungsten atoms that lead to the observed space group P4/ncc.

Crystallite Nanosize Effect on the Structural Transitions of WO3 Studied by Raman Spectroscopy

“…(18). The aerosol of (NH 4 ) 10 the pyrosol process followed by a subsequent spectral control under a low laser power excitation. This process was interrupted when the spectrum was found close to the one considered as representative of the 16(75) nm size.…”

Structural and optical properties of visible active photocatalytic WO3 thin films prepared by reactive dc magnetron sputtering

“…WO 3 exists in several phases, which differ with respect to each other by the tilting and displacement of the atoms in the octahedral building blocks that comprise the WO 3 structure. The thermodynamically favored phase is reported to change with temperature (at standard pressure) for crystalline bulk WO 3 as follows: monoclinic Pc (e-WO 3 ) up to 230 K, triclinic P1 (d-WO 3 ) 230-300 K, monoclinic P2 1 /n (c-WO 3 ) 300-623 K, orthorhombic Pnma (b-WO 3 ) 623-1020 K, tetragonal P4/ncc (a-WO 3 ) 1020-1171 K, and, finally, tetragonal P4/nmm (a-WO 3 ) to the melting point at 1700 K. [22][23][24][25][26] The stability of each of these phases is modified by preparation procedures. For nanocrystalline thin films, the detailed growth conditions are critical, including type of substrate, temperature, and pressure.…”

First-principles reinvestigation of bulk WO3

“…At higher temperatures, Vogt et al [22] and Locherer 62 et al [19] concluded a transition from P bcn to the P 4/ncc 63 phase and Howard et al [23] observed an intermediate P 2 1 /c 64 phase. Lochereret al [19] and Woodward et al [26] found 65 an additional transition from P 4/ncc to P 4/nmm at 980 to 66 1200 K. Below room temperature, Salje et al [20] reported 67 a transition from the triclinic P1 phase to a polar phase (P c) 68 with no further transitions down to 5 K.…”