IMPROVED THERMAL-CONDUCTIVITY IN ISOTOPICALLY ENRICHED CHEMICAL-VAPOR-DEPOSITED DIAMOND

The thermal conductivity kappa of an isotopically enriched (0.055% C-13) polycrystalline diamond plate made by chemical vapor deposition (CVD) has been measured for heat flowing in a direction either parallel (kappa(parallel-to)) or perpendicular (kappa(perpendicular-to)) to the plane of the plate. The room-temperature conductivities kappa(parallel-to)=21.8 and kappa(perpendicular-to) = 26 W cm-1 K-1) are higher than for any CVD diamond previously reported, and the kappa(perpendicular-to) value is higher than the best gem-quality single crystal with the natural abundance (1.1%) of C-13. Analysis of the temperature dependence of kappa(parallel-to) reveals that the point-defect scattering of phonons is in fact significantly lower than expected for the natural abundance of C-13 and that it is responsible for the improved conductivity. The observed anisotropy kappa(parallel-to)/kappa(perpendicular-to) = 0.84 at room temperature is associated with the anisotropic grain structure.