Ultrahard stitching of nanotwinned diamond and cubic boron nitride in C2-BN composite

Abstract Materials combining the hardness and strength of diamond with the higher thermal stability of cubic boron nitride ( c BN) have broad potential value in science and engineering. Reacting nanodiamond with c BN at moderate pressures and high temperatures provides a pathway to such materials. Here we report the fabrication of C x -BN nanocomposites, measuring up to 10 mm in longest dimension, by reacting nanodiamond with pre-synthesized c BN in a large-volume press. The nanocomposites consist of randomly-oriented diamond and c BN domains stitched together by sp 3 -hybridized C-B and C-N bonds, leading to p -type semiconductivity. Dislocations near the sutures accommodate lattice mismatch between diamond and c BN. Nanotwinning within both diamond and c BN domains further contributes to a bulk hardness ~50% higher than sintered c BN. The nanocomposite of C 2 -BN exhibits p -type semiconductivity with low activation energy and high thermal stability, making it a functional, ultrahard substance.