A comparison of the effect of radiation on the thermal conductivity of sapphire at low and high temperatures

The effects of radiation on the thermal conductivity of sapphire have been calculated over a wide temperature range (77-400 K). The phonon scattering relaxation times for various scattering mechanisms have been analyzed in order to determine the effect each mechanism has on the lattice thermal conductivity of sapphire. The methods of calculation at low and high temperature are reviewed, and the results of these calculations are presented to compare the effect at different temperatures. It is found that vacancy scattering can significantly reduce the thermal conductivity over a wide temperature range; for example, a vacancy concentration of 0.01 per atom leads to a fractional change of about 90% at 77 K versus 43% at 400 K. This reduction has significance for the design and placement of radio frequency and microwave windows in fusion reactors. ((orig.))