Vibrational States in Opals Revisited

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 hyd...

Full description

Saved in:
Bibliographic Details
Published in:Journal of physical chemistry. C 2011-06, Vol.115 (24), p.11968-11975
Main Authors: Ivanov, V. G, Reyes, B. Aguilar, Fritsch, E, Faulques, E
Format: Article
Language:English
Subjects:
C: Nanops and Nanostructures
Condensed Matter
Materials Science
Physics
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary: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 ∼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.
ISSN:1932-7447
1932-7455
DOI:10.1021/jp2027115