Low-Temperature Polymorphism in Tungsten Trioxide Powders and Its Dependence on Mechanical Treatments

✍ Scribed by E. Cazzanelli; C. Vinegoni; G. Mariotto; A. Kuzmin; J. Purans

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 194 KB
• Volume: 143
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.8061

✦ Synopsis

The polymorphism of WO 3 powder samples, resulting from mild mechanical treatments and from temperature changes between 30 K and room temperature, has been investigated by using Raman spectroscopy and X-ray diffraction. A transition from the monoclinic (I) -phase to the triclinic -phase after moderate mechanical treatments has been observed for untreated powder, just what happens when the same samples are rapidly cooled to low-temperature. Evidences of the low temperature monoclinic (II) polar -phase have been found at room temperature in samples after a stronger milling treatment. The sequence of the low-temperature phase transitions appears to be strongly dependent on the mechanical history of the powders. A new lowtemperature N-phase has been observed below about 200 K in different samples: it is the main phase in commercial untreated powders, having the monoclinic (I) -phase at room temperature, but constitutes only a small fraction in moderately treated powders, having the triclinic -phase at room temperature.