Thermal Conductivity of Alkali Halide Crystals Containing the Hydroxide Ion

Thermal-conductivity measurements have been performed from 0.34 to 80°K for alkali halide crystals containing the hydroxide ion as an impurity. For sodium chloride containing hydroxide, bowl-shaped thermal-conductivity curves are measured between 0.4 and 0.9°K; the form of these curves is believed to arise from more than one tunneling energy level of hydroxide in the 0.9- to 2.8-${\mathrm{cm}}^{-1\mathrm{}}$ region. Thermal-conductivity measurements on potassium chloride containing hydroxide suggest the existence of tunneling levels immediately below 0.3°K. Similar measurements on rubidium chloride and potassium iodide with hydroxide suggest the existence of tunneling levels considerably below 0.3°K, with the scattering stronger in the latter system. The tunneling levels of sodium-chloride-sodium-hydroxide show no isotopic dependence when deuteroxide O${\mathrm{D}}^{-}$ is substituted for hydroxide O${\mathrm{H}}^{-}$. Measurements on lightly doped hydroxide samples were complicated by the presence of significant amounts of divalent calcium impurity that destroys the excited energy levels of hydroxide. The thermal-conductivity data in KCl and NaCl have been fitted quantitatively by computer computations using the Debye thermal-conductivity integral. Resonance phonon scattering rates were used which incorporate temperature-dependent widths as essentially the only adjustable parameters, plus frequency-dependent imaginary parts in the resonance denominators. In some cases the widths determined this way are in good agreement with other data on the linewidths.