Phase transitions in tungsten trioxide at high temperatures - a new look

Abstract

Neutron powder diffraction results on the tetragonal-orthorhombic and orthorhombicmonoclinic structural phase transitions of tungsten oxide are reported. The observed first-order transition from P 4/ncc to P nma at 980 K to 1200 K hides the transition from the highertemperature phase P 4/nmm (via Cmca) to P nma. At 623(24) K, P nma transforms via octahedral rotations in a tricritical transition to P 2 1 /n. The structural characteristics and thermodynamic properties of the order parameters are described in detail. The evolution of the WO 6 octahedra and the atomic positions is documented using such parameters as the octahedral elongation, octahedral variance and the off-centre displacement vectors for the tungsten atoms. It is shown that the phase transitions can be adequately described within the framework of a decoupled mean-field Landau theory.

Electrical and optical properties of mixed phase tungsten trioxide films grown by laser pyrolysis

“…At room temperature, WO 3 usually exists as a mixture of monoclinic () and triclinic () crystal phase structure, and undergoes phase changes to higher symmetries upon heating [8][9][10][11][12]. WO 3 has commonly been studied for its electro-chromic, gaso-chromic and photo-chromic properties.…”

Phase transition in WO3 microcrystals obtained by sintering process

“…The phase transitions in WO 3 at high temperatures were reviewed in detail by means of neutron powder diffraction and within the framework of meanfield Landau theory. 11 Recently, it was reported that WO 3 x presents sheet superconductivity and the oxygen vacancies stabilizes, at room temperature, the high-temperature tetragonal phase (space group P42 1 m). 15 -17 Two phase transitions occur below room temperature: the monoclinic (V) phase (space group P2 1 /n) changes to the triclinic (VI) phase (space group P1) at about 290 K, and the triclinic (VI) phase changes to a new monoclinic (VII) ferroelectric phase (space group Pc) at about 233 K. These low-temperature phase transitions were studied through several experimental techniques such Ł as x-ray and neutron diffraction, 5 -8,11,16,17 Raman scattering, 9 infrared spectroscopy and dielectric measurements.…”

First-principles reinvestigation of bulk WO3

“…1. A monoclinic phase (P 2 1 /n) 60 [21] and a triclinic phase P1 exist at room temperature 61 [25,26]. 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.…”