High-pressure synthesis and characterization of superconducting boron-doped diamond

Microcrystalline powders of boron-doped diamond were produced in the C-H-B system under a pressure of 8 GPa and at a temperature of more than 2000 K. The presence of boron in the C-B-H system was shown to decrease the temperature-pressure parameters for diamond synthesis compared with those for the binary C-H system (naphthalene). A decrease in the parameters for synthesis in the system with boron may be due to the formation of graphite with less perfect crystal structure during an intermediate stage of diamond formation. Superconducting diamond microcrystals are synthesized in the C-H-B system with boron content of about 5-10 at% in a mixture with naphthalene. Superconductivity below 3.5 K in boron-doped diamond powder is detected in AC magnetic susceptibility measurements.