Temperature Dependence of the Elastic Constants of the Alkali Halides. I. NaCl, KCl, and KBr

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Abstract
The elastic constants of NaCl, KCl, and KBr have been measured from room temperature to temperatures near their melting points. A phase‐comparison technique was used to measure the velocity of high‐frequency sound waves in the crystals from which the elastic constants were derived. The elastic constants obtained were found to agree, within experimental error, with previously measured values. The theoretical values of the temperature dependence calculated from the expressions of Mitskevich agree very well with the experimentally obtained values. The value and temperature dependence at high temperatures of the elastic constants (c11–c12)/2 are compared to the relative melting temperatures of the three crystals. In support of the theory of Thompson, the rapid decrease of this elastic constant can be correlated with the relative temperature of melting.