Relaxation Phenomena

Abstract

Modulation calorimetry provides opportunity to vary in a wide range the frequency of the temperature oscillations in a sample. This makes possible a search for relaxation phenomena in specific heat, which appear when the modulation period becomes comparable to the relaxation time of a process contributing to the specific heat. Three such phenomena have been found by modulation calorimetry. First, supercooled organic liquids were studied near glass transitions. In this region, the specific heat becomes complex and frequency dependent (Birge and Nagel 1985, 1987; Birge 1986). Second, a relaxation phenomenon in the specific heat of tungsten and platinum was found at modulation frequencies of the order of 10⁵ Hz (Kraftmakher 1985, 1990). The phenomenon was attributed to equilibration of point defects in crystal lattice. Finally, a relaxation was observed in the lowtemperature specific heat of Mn₁₂ acetate crystal (Fominaya et al. 1999b) and in some other cases.