Low-frequency internal friction in silica glass

¹  Dipartimento di Fisica, Università di Perugia - I-06123 Perugia, Italy
²  Istituto Nazionale di Fisica Nucleare, VIRGO Project Sezione di Perugia - I-06123 Perugia, Italy
³  Dipartimento di Fisica, Università di Camerino - I-62032 Camerino, Italy
⁴  Michigan Center for Theoretical Physics, The University of Michigan - Ann Arbor, MI 48109-1120, USA

Received: 14 May 2007
Accepted: 9 October 2007

Abstract

Precise low-frequency internal friction measurements on vitreous silica, taken over a wide temperature (4 K < T < 300 K) and frequency range (40 Hz < ν < 14 kHz), show remarkable similarities, but also suggestive differences with recent light scattering experiments. In the interval 30 K < T < 110 K, the exponent α of the power law relaxational spectrum turns out to be proportional to , with a minimum at around T_k = 13 K. This phenomenon is interpreted as a manifestation of thermal activation in an asymmetric double well system, the asymmetry being associated to quenched spatial disorder. For T > 160 K the loss angle develops a distinct step-like structure followed by a plateau, both independent of ν, thus signalling the onset of a competing relaxation mechanism with much higher an activation energy.