The High-Temperature Phases of WO3

✍ Scribed by Tom Vogt; Patrick M Woodward; Brett A Hunter

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 196 KB
• Volume: 144
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8173

✦ Synopsis

High-temperature, high-resolution neutron powder diffraction experiments were performed to investigate the phases of WO3 between room temperature and 850°C. Two phases were found and characterized by Rietveld refinements: orthorhombic -WO3 (Pbcn, a ‫؍‬ 7.3331(2), b ‫؍‬ 7.5733(2), c ‫؍‬ 7.7401(3) A s at 350°C, tilt system a 0 b ؉ c ؊ ) and tetragonal -WO3 (P4/ncc, a ‫؍‬ 5.2759(1), b ‫؍‬ 5.2759(1), c ‫؍‬ 7.8462(3) A s at 800°C, tilt system a 0 a 0 c ؊ ). The sequence of temperature-induced phase transitions in WO3 can be rationalized in terms of changes in the octahedral tilt systems and/or displacements of the tungsten out of the center of the WO6 octahedron. Above room temperature the two phase transitions are driven by sucessive softening of phonon modes, M3 at the -to -transition and R25 at the -totransition.