Synthesis and Thermal Conductivity of Boron-Doped and 12C-Enriched Diamond Single Crystals

Boron-doped 12C-enriched diamond single crystals (about 3 mm; 99.97% 12C) were successfully synthesized at 6.1 GPa and 1430 °C by the high-pressure and high-temperature method using a starting mixture of boron powder and 12C-enriched pyrolytic carbon powder. The thermal conductivities of these crystals were determined to be 30.6 W/cm·K (3.4 ppm effective acceptor concentration) and 27.1 W/cm·K (34 ppm effective acceptor concentration; highly doped) by a cut-bar steady-state conduction technique. The conductivity of the highly-doped crystals was 9% lower than that of similarly synthesized non-doped 12C-enriched crystals (99.97% 12C), whereas those of the boron-doped 12C-enriched crystals were higher than that of similarly synthesized non-doped naturally abundant crystals (99.0% 12C), indicating the isotope effect in the boron-doped 12C-enriched crystals.