Thermal conductivity of LaF3:0.1%Er3+ from 1.6K to 100K

Measurements of the thermal conductivity of LaF3:0.1%Er3+ have been taken from 1.6K to 100K using standard steady state techniques. The ionic conductor behaves thermally as an insulator in the temperature range of the experiment. The hexamolecular unit cell crystallizes with D/sub 4h/3 symmetry giving 72 phonon branches. Two of the 69 optical branches are known to lie extremely low in the Brillouin zone. The thermal conductivity was investigated to determine the effect of erbium doping on the heat flow, and, additionally, to determine whether acoustical-optical phonon scattering is important. The data were fit using the Debye-Callaway integral with a parametric relaxation time. Comparison of the fit to the fit for the undoped material reveals that good correspondence can be obtained without having to alter phonon-phonon scattering rates, but leads to higher dislocation densities than expected, and disagreement between the point defect rates. Introduction of neither spin-phonon nor optical-acoustical relaxation terms was necessary to improve the fits