Crystallite Nanosize Effect on the Structural Transitions of WO3 Studied by Raman Spectroscopy |
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Authors: | M BoulovaG Lucazeau |
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Institution: | a Chemistry Department, Moscow State University, Moscow, 119899, Russiab Laboratoire d'Électrochimie et de Physico-Chimie des Matériaux et des Interfaces, INPG-CNRS, 1130 rue de la Piscine, 75, 38402, St Martin d'Hères, Cedex, France |
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Abstract: | Nanocrystallites of tungsten oxide samples of 2, 4, 16, 35 and 60 nm of diameter were prepared by cryosol and pyrosol techniques. The pressure- and temperature-induced phase transitions of these samples were monitored by Raman spectrometry from 0.1 MPa to 34 GPa and from 77 to 1200 K. The tetragonal (α)-orthorhombic (β)-monoclinic (γ) transitions in these nanometric samples are strongly downshifted in temperature by comparison with the bulk WO3. For instance, the tetragonal phase which exists above 1171 K for the bulk tungsten oxide can be stabilized at 700 K for the 35 nm sample. In the same way, the monoclinic P21/n-monoclinic P21/c high-pressure-induced transition is slightly shifted from 0.1 GPa to a higher pressure (1.5 GPa). The discussion of these transition-line shifts is based on thermodynamic considerations in which the surface energy of crystallites plays an important role. |
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Keywords: | tungsten oxide nano-crystalline materials phase transition Raman spectroscopy high pressure |
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