Temperature Dependence of the Elastic Constants of the Alkali Halides. II. The Solid Solution KCl–KBr

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The elastic constants for the solid solution KCl–KBr have been measured from room temperature to 400°C. The general trend of the elastic constants versus composition is in agreement with theory but indicates that the dependence on interionic distance is greater than predicted theoretically. The temperature coefficients of the elastic constants are found to agree fairly well with the theory of Mitskevich for c11 and ½(c11–c12), but those for c44 were best fit by an expression taken from Leibfried and Hahn. The dependence on composition of ½(c11–c12) at high temperature strongly supports the theory of Thompson that melting is due to the instability of the acoustic mode associated with this shear elastic constant.