A. Bartolotta et al., A study of Raman spectroscopy and low-temperature specific heat in gel-synthesized amorphous silica, J NON-CRYST, 280(1-3), 2001, pp. 249-254
A comparative study of low-temperature specific heat (1.5-25 K), C-p, and l
ow-frequency Raman scattering (< 150 cm(-1)) has been performed in amorphou
s silica samples synthesized by sol-gel method (xerogels) and thermally den
sified in a range of densities, from rho = 1250 kg m(-3) to rho = 2100 kg m
(-3), close to the density of the melt quenched vitreous silica (v-SiO2). T
he present analysis concerns the application of the low-energy vibrational
dynamics as an appropriate tool for monitoring the progressive thermal dens
ification of silica gels. By comparison with v-SiO2, the Raman and thermal
properties of xerogels with increasing thermal treatment temperature reveal
ed the following important results: (i) the existence of a critical treatme
nt temperature at about 870 degreesC, where a homogeneous viscous sintering
produces full densification of the samples. This effect is detected by the
observations of the Boson peak in Raman spectra at about 45 cm(-1) and of
a peak in C-p(T)T (3), very close to those observed in v-SiO2; (ii) in sili
ca xerogels treated at temperatures less than about 800 degreesC, the low-f
requency Raman scattering is greater, with a continuous decreasing unstruct
ured shape, and the Boson peak is not detected in the spectra. (C) 2001 Els
evier Science B.V. All rights reserved.