Low-temperature polymorphism in tungsten trioxide powders and its dependence on mechanical treatments
- Univ. della Calabria, Cosenza (Italy)
- Univ. di Trento (Italy)
- Univ. of Latvia, Riga (Latvia). Inst. of Solid State Physics
The polymorphism of WO{sub 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) {gamma}-phase to the triclinic {delta}-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 {var_epsilon}-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 low-temperature 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) {gamma}-phase at room temperature, but constitutes only a small fraction in moderately treated powders, having the triclinic {delta}-phase at room temperature.
- OSTI ID:
- 349910
- Journal Information:
- Journal of Solid State Chemistry, Vol. 143, Issue 1; Other Information: PBD: 15 Feb 1999
- Country of Publication:
- United States
- Language:
- English
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