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Ivanov, V. G., Aguilar Reyes, B., Fritsch, E. & Faulques, E. (2011) Vibrational States in Opals Revisited. J. Phys. Chem. C, 115 11968–11975. 
Added by: Laurent Cournède (2016-03-10 21:32:20)
Type de référence: Article
DOI: 10.1021/jp2027115
Numéro d'identification (ISBN etc.): 1932-7447
Clé BibTeX: Ivanov2011
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Catégories: MIOPS
Mots-clés: dynamics, field, force-constants, glasses, raman-spectroscopy, rings, sio2, spectra, vitreous silica
Créateurs: Aguilar Reyes, Faulques, Fritsch, Ivanov
Collection: J. Phys. Chem. C
Consultations : 5/436
Indice de consultation : 2%
Indice de popularité : 0.5%
Résumé     
Quantitative assessment of the vibrational features of nanocrystalline hydrated silicas is still not yet ascertained, although this is a relevant issue in silica physics. In this work, we examine the vibrational states in two generic opaline silicas. PM3 semiempirical calculations on finite SiO2 hydrated clusters prove that the low-frequency Raman lines experimentally observed at similar to 307, 340, and 370 cm(-1) and the high-frequency ones at 790 cm(-1) and 1080 cm(-1) stem from O-Si-O bending vibrations in six-membered rings of corner-shared SiO4 tetrahedra and O-Si-O symmetric/asymmetric stretch vibrations, respectively. Lattice dynamical calculations on crystalline silica polymorphs show that the predominance of tridymite over cristobalite in opaline silicas cannot be established due to the intrinsic nanoscale crystalline order of the materials. We conclude that the vibrational variations observed between opaline silicas are due to gradual formations of six-membered rings in a disordered SiO2 matrix.
Added by: Laurent Cournède  
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