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

摘要

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 B_(13)N_2 has been synthesized by crystallization from the B–BN melt at 5 GPa. The structure of B_(13)N_2 belongs to the R-3m space group (a = 5.4455(2)A , c = 12.2649(9)A ) 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 ‘‘B_6N’’ and ‘‘B_(50)N_2’’ has been observed. Their structures seem to be much more sophisticated and have not been even resolved to present time.