12 - Measurements of Heat Capacity

Abstract

The knowledge of low-temperature specific heat is extremely important to understand the physical properties of a solid. This chapter focuses on the measurements of heat capacity. These measurements are not, conceptually, more difficult than those of thermal conductivity. On the contrary, some problems such as the anisotropy of materials are not present, and the shape of the sample to be measured is usually unimportant. From a technical point of view, the measurements of heat capacity are more complex. One reason is that since thermometers contribute to the addendum heat capacity, it is necessary in most cases to use crystalline thermometers of small heat capacity. Furthermore, the characteristic times of the heat capacity measurements are strongly limited by the instrumentation time response (typically 0.1 s). The five most common methods used to measure the heat capacities at low temperature are described: the heat pulse technique; the AC calorimetry; the time constant (relaxation) method; the dual slope method; and the method of the thermal bath modulation. Three examples of measurement of heat capacity are reported: a crystal with a negligible addendum; a polymer with a heavy addendum; and carrier specific heat of a heavily doped semiconductor.