Single-crystal synthesis of highly thermal conductive 12C-enriched diamond from pyrolytic carbon powder by the high-pressure, high-temperature method

We have examined the possibility of synthesis of 12C-enriched diamond single crystal by a conventional temperature gradient method at high pressure and high temperature using a starting material of a carbon powder source prepared via pyrolysis of 12C-enriched methane. 12C-enriched diamond single crystal (about 3 mm in diameter) was successfully grown at 1430 °C, 6.1 GPa using a 12C-enriched pyrolytic carbon source prepared from 12C-enriched methane (1 to 5 Torr) at 1800 °C. Thermal conductivity of the 12C-enriched diamond single crystal was measured by a modified specimen arrangement of a cut-bar steady-state conduction technique. The result showed that thermal conductivity of the 12C-enriched diamond single crystal (99.97% 12C) was 29.9 W/cm-K, and it was found to be 32% higher than that of similarly synthesized naturally abundant diamond single crystal (99.0% 12C), indicating the isotope effect of diamond.