Specific Heat of LiF and KI at Low Temperatures

Abstract

The heat capacities of LiF and KI single crystals have been measured over the temperature range 2-7°K. An adiabatic calorimeter was employed making use of a mechanical contact "heat switch." A carbon resistor embedded directly in the specimen was used as thermometer. For LiF the heat capacity was found to be proportional to the cube of the temperature over the whole range of temperatures investigated, and the value of ${\theta }_0$ was found to be 722°K. For KI variations from the $T^3$ dependence were found above 3°K. An extrapolation of a smooth curve through the data to zero degrees temperature indicates a value of ${\theta }_0=128\mathrm{}°$K. These values of ${\theta }_0$ are compared to values of ${\theta }_0$ derived from elastic constants data.