On the increase of thermal conductivity in glasses above the plateau region

Hopping of localized vibrational states in glassy systems via vibrational anharmonicity, C-eff, provides an additional heat-carrying channel. The associated thermal conductivity, kappa(hop)(T), increases linearly with increasing temperature T in the regime where vibrational lifetimes are reasonably long. Recent work of Yamaguchi et al. has shown that, for a-GeS2 C-eff for the strongly localized states associated with the Bose peak is at least 20 times larger than the acoustic anharmonicity C-111. Insertion of this value into the theoretical expression for kappa(hop)(T), along with accepted values for the other parameters, yields a magnitude for kappa(T) quite comparable to that found for network-forming glasses above the plateau temperature. (C) 1999 Elsevier Science B.V. All rights reserved.