Superhard boron-rich borides and studies of the BCN system

The crystal chemistry of the B4C-type structures is described. New structural data for B12S, B13Se and B6O are presented. It is found that B6O with a microhardness larger than that of B4C invariably contains a high concentration of vacancies at the oxygen position (B6O1-x with x in the range 0.76–0.84). Structural results for graphite-like phases in the B-C-N system are presented and discussed.