Phonon Scattering in KCl-KBr Solid Solutions at Low Temperatures

Abstract

The scattering of phonons by point defects at liquid helium temperatures has been studied. Single crystals of KCl-KBr solid solutions were employed, since it is known that the ${\mathrm{Cl}}^{-}$ and ${\mathrm{Br}}^{-}$ ions are randomly distributed in the anion lattice sites. A 1 mole percent addition of KBr reduced the conductivity of KCl by a factor of three. For all the crystals measured, including pure KCl and pure KBr, the thermal conductivity showed a maximum at the same temperature (5°K). Hence, point defects reduce the conductivity on both the high- and low-temperature sides of the maximum. For the mixed crystals the thermal conductivity was found to be related to the absolute temperature by the empirical formula $K=K_0{e}^{-0.099T}$ for the temperature interval 6°K to 16°K.