Thermal transport in deformed lithium fluoride

The thermal conductivities 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 irradiation suggests that the active defects are fluttering dislocations. At T2 K essentially all phonons are scattered by defects. Above 2 K the reduction in 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 T2 K.