Dielectric measurements of silica aerogels

Abstract

The dielectric response of aerogels of silica is measured down to 1.7 K and compared to a theoretical calculation using the Looyenga's relation applied to two different model structures. Helium atoms start to condense on the pore walls at T — 13K and fill them at the liquefaction temperature. A drop of the dielectric constant accompanied by a large loss peak is observed near 35K. The origin of the absorption lies in a thermally activated relaxation process and is probably due to a large number of structural defects similar to those proposed for bulk silica.