Debye temperatures of KCl, KBr and RbCl by X-ray diffraction

Debye temperatures of KCl, KBr and RbCl have been determined by X-ray diffraction from room temperature up to about 800°K using methods due to Paskin [Acta Cryst. (1957). 10, 667–669] and Chipman [J. Appl. Phys. (1960). 31, 2012]. The anharmonic contribution to the Debye Θ is shown to come essentially from thermal expansion. The plot of the reduced thermal expansion α/α_m/2 versus T/Aa²θ² gives a common curve for all the three halides. Here α_m/2 is the value of α at T = ½ T_m, T_m being the melting point, A is the mean atomic weight and a the lattice constant. An equation relating α, T and θ for the alkali halides is established for the first time. The values of the root mean square amplitudes (u²)^½, are calculated for the alkali halides from the equation and are compared with those of other workers.