Temperature Dependence of the Bulk Modulus of Alkali Halides

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Abstract
There is very little data on the behavior of the bulk modulus of crystals over a wide temperature range. Recently, Anderson revived interest in a fundamental constant of a solid called δ, which was first introduced by Grüneisen. This parameter is similar in many respects to the well‐known Grüneisen parameter γ and was used by Anderson to explain the temperature dependence of the bulk modulus of oxide compounds. In the present paper, general expressions for δ have been derived in a simple manner correlating the thermodynamical and the interatomic potential approaches. The parameter δ has also been related to the Grüneisen parameter using the Slater and Dugdale‐MacDonald equations. The relative appropriateness of different expressions for δ has been discussed. The computed values of δ for NaCl‐ and CsCl‐type alkali halides based on the Born‐Mayer and the modified Born‐Mayer potential forms have been reported and are found to be consistent and in essential agreement with other determinations. These values have been used to calculate the adiabatic bulk modulus as a function of temperature for KCl and NaCl. A good agreement is found with the experimental data over most of the temperature range in the neighborhood of and above the room temperature. This general accord with the predictions of theory clearly indicates that in the temperature range where the experimental data is inadequate, it is possible to predict the temperature dependence of the bulk modulus of nonoxide compounds also, using Anderson's equation and the relationships for δ developed in the present paper.