Thermal transport in deformed lithium fluoride

Abstract

The thermal conductivities $\kappa$ of LiF crystals, deformed by compression, have been measured over the temperature range 0.05-5 K. Below ∼2 K a fraction of the thermal phonons are scattered strongly by defects while another fraction is only weakly scattered and can propagate distances of ∼1 cm even in heavily deformed LiF. The fact that the strong scattering can be suppressed by modest $\gamma$ irradiation suggests that the active defects are fluttering dislocations. At $T\gtrsim 2$ K essentially all phonons are scattered by defects. Above 2 K the reduction in $\kappa$ with deformation depends on the density of defects or impurities previously present in the sample. Available evidence suggests that isolated dislocations are not responsible for the strong phonon scattering at $T\gtrsim 2$ K.