Superhard and superconductive polycrystalline boron doped diamond synthesized with different concentration of B4C

Boron doped diamond are potential superhard materials with good electric conductivity . In this work, polycrystalline boron doped diamond (p-BDD) with different boron concentration were synthesized from the mixture of graphite and boron carbide under ultra-high pressure (15 GPa) and temperature (2500–2700 K). The results indicate that no more boron atoms can be inserted into diamond when the boron concentration is above 4 at%. The EELS spectra indicated that the boron atoms have been doped into the diamond grains, and surplus boron carbide locate at the grain boundary. The hardness measurements reveal that the p-BDD doped with 1 at% and 23 at% boron atoms exhibit high hardness of 78.5 GPa and 45 GPa, respectively, which is equivalent to the hardness of single crystal diamond and cubic boron nitride . The p-BDD is a semiconductor and transforms into superconductive state below 2.5 K. According to microstructure measurements, highly dense p-BDD and B 4 C bonded diamond exhibit superhard behavior because of the strong bonding of diamond grains by B 4 C additives. The oxidation temperature of these p-BDD specimens is around 1538 K in the air, which is far higher than diamond. B 4 C is demonstrated as a superior additive to sinter superhard and electric conductive p-BDD, which are extremely useful in areas where high hardness and electric conductive are highly desired.