Mechanical Spectroscopy and other Relaxation Spectroscopies

Abstract

Mechanical spectroscopy is a powerful technique in investigations of the molecular mobility, atomic interactions, and more particularly the structural defects in matter. In crystalline materials, the problem is mainly dealing with point defects, dislocations, and their interactions. As a general rule, large frequency and temperature ranges are required in order to capture the characteristics of these defects at a microscopic level, namely the dynamics and the concentration. In the case of non-crystalline solids, the low temperature relaxation processes obey the Arrhenius law (i.e. the atomic or molecular motions are individual). If the temperature is not far below the liquid glass transition, the internal degrees of freedom are no more independent and thus enter a cooperative regime. The wide band mechanical spectroscopy appears to be necessary for the complete analysis of the complex dynamics of such systems. In addition, complementary relaxation spectroscopies (e.g. dielectric spectroscopy, NMR), in combination with non elastic radiation scattering are shown to provide a clear understanding of the dynamics and structure at a microscopic level.