Specific Heat and Elastic Constants of Sodium Iodide at Low Temperatures

Abstract

Measurement of specific heat from 2.4°K to 8°K and of elastic constants from 4.2°K to 300°K have been made on single crystals of sodium iodide. The Debye theta at 0°K, ${\theta }_0$, as calculated from the specific heat data is 163±1°K. Values of the elastic constants at 4.2°K are $C_{11}=3.761\mathrm{}$, $C_{12}=0.798\mathrm{}$, and $C_{44}=0.781\mathrm{}$ in units of ${10}^{11}$ dynes/${\mathrm{cm}}^2$. ${\theta }_0$ calculated from the velocity of sound waves is 167±1.5°K. The manner in which the experimental specific heat compares with the work of Berg and Morrison and with the theoretical concepts of Barron and Morrison is discussed.