Low-temperature energy excitations and thermal properties of silica aerogels

Abstract

We present measurements of specific heat, thermal conductivity, internal friction, and relative change in sound velocity in the temperature range 0.1--10 K on several base-catalyzed and neutral-reacted low-density silica aerogels (\ensuremath{\rho}: 0.87--0.12 g/${\mathrm{cm}}^{3}$). The results show important differences in the behavior of classical disordered dense solids (a-${\mathrm{SiO}}_{2}$). They are analyzed within the framework of an elastic model of rods assembled in a disordered hierarchical network.