Low-energy lattice vibrations of porous silica glass

Publisher Website
Google Scholar
Abstract
Internal friction, speed of sound, and thermal conductivity of Vycor glass with porosities ranging from 29% to 36% have been measured from 65 mK to 300 K. The results have been compared with those obtained on bulk amorphous silica in order to understand how the porous structure affects the low-energy tunneling states. Contrary to specific-heat results reported previously on Vycor, our measurements indicate that these changes are surprisingly small. Our findings agree qualitatively with the results reported previously on sol-gel porous glass with a similar porosity, and also on aerogels, which are even more highly porous than Vycor. Analysis of the porous silica data suggests that the porosity has very little influence on the spectral density of the tunneling defects, while their coupling energy to the phonons scales with the speed of sound. The excitations observed in specific heat, however, appear to be different from those observed in the acoustic and thermal-conductivity experiments.

This publication has 50 references indexed in Scilit: