Thermal transport in deformed lithium fluoride

The thermal conductivities κ 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 γ irradiation suggests that the active defects are fluttering dislocations. At T≳2 K essentially all phonons are scattered by defects. Above 2 K the reduction in κ 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≳2 K.