Elastic Constants of the CsCl Structure Containing Impurity Ions

The $T$-matrix method has been used in determining the effect of point defects on the elastic properties of the crystals having a CsCl structure. The expressions for the bulk elastic constants have been obtained in terms of the local changes in the central- and the noncentralforce constants. A numerical estimate has been made in the case of CsI containing some impurity ions such as ${\mathrm{Rb}}^{+}$, ${\mathrm{K}}^{+}$, ${\mathrm{Tl}}^{+}$, and ${\mathrm{In}}^{+}$. The necessary force-constant changes have been taken from the results of the infrared lattice-absorption experiments. The calculated elastic constants have been tentatively compared with the experimentally measured elastic constants of a dilute alloy Mo-Re which has a bcc structure. Agreement is seen in the relative magnitudes of change in the elastic constants.