Chemical interaction in the B–BN system at high pressures and temperatures.: Synthesis of novel boron subnitrides

Chemical interaction and phase transformations in the B–BN system have been in situ studied by X-ray diffraction with synchrotron radiation at pressures up to 5.3 GPa and temperatures up to 2800 K using multianvil press. New rhombohedral boron subnitride B13N2 has been synthesized by crystallization from the B–BN melt at 5 GPa. The structure of B13N2 belongs to the R-3m space group (a=5.4455(2) Å, c=12.2649(9) Å) and represents a new structural type. The subnitride is an individual compound and not a solid solution, in contrast to boron carbide. Besides, the formation of two other boron-rich B–N phases denoted as “B6N” and “B50N2” has been observed. Their structures seem to be much more sophisticated and have not been even resolved to present time.