Specific Heat of LiF and KI at Low Temperatures

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 θ₀ was found to be 722^∘{}K. For KI variations from the T³ dependence were found above 3^∘{}K. An extrapolation of a smooth curve through the data to zero degrees temperature indicates a value of θ₀=128^∘K. These values of θ₀ are compared to values of θ₀ derived from elastic constants data.