The observed dielectric response of most materials is seldom in accord with Debye behaviour, but has been found experimentally to exhibit a remarkable ‘universality.’ It is proposed that this universality is a consequence of some ubiquitous correlated states which exhibit an infrared (IR) divergent-like response to induced transitions of the polarising species.

On the origin of the universal dielectric response in condensed matter

Publisher Summary This chapter provides evidence that below 1 K, the thermal properties of amorphous insulating solids differ markedly from their crystalline counterparts. The specific heat of amorphous solids is much larger than that of crystals, whereas their thermal conductivity is considerably lower. In pure and defect-free dielectric crystals, both quantities are proportional to T3 at temperatures below 1 K. In amorphous solids, however, the specific heat is almost linear and the thermal conductivity varies almost quadratically with temperature. The tunneling model provides a good phenomenological basis on which various observations are explained. This is the main achievement of the past decade of extensive investigations. The chapter also studies the low temperature anomalies with a much broader perspective and not in isolation, as a problem in it. It is a property of the glassy state in general and a connection should exist between low temperature anomalies and other properties of glasses. It is hoped that such an approach will lead to new ideas and directions and maybe to further surprises.

Chapter 3: Thermal and Elastic Anomalies in Glasses at Low Temperatures

Single crystals of nonstoichiometric β alumina 11 Al2O3, (1+x)M2O3(x = 0.25 to 0.6) with M = Na, K, Tl, Ag have been studied by Raman spectroscopy between 2 and 1000 cm−1 in the 20–1400 K temperature range. Far infrared measurements have been performed between 10 and 250 cm−1. Ag(Ag)3 and (Tl)3 clusters of coupled cations have been evidenced in the low temperature spectra of Ag+ and Tl+ compounds. Ag–Ag and Tl–Tl ’’bond stretching’’ force constants were found equal, respectively, to 0.10 and 0.23 mdyn A−1. In the low temperature state, potential barriers separating sites available for cations have been found to increase at a small extent from x = 0 to x = 0.6 compounds. The temperature dependence of the low frequency Raman spectra is reported and shows that vibrational correlations between silver ions are partly responsible for the decrease of the energy necessary for the cation hopping mechanism.

F. L. S. Hsu

Papers

Low-temperature heat capacity of alkali-metal and silver β-aluminas