ABSTRACT
Boron nitrides are known to have several polymorphic modifications, i.e., hexagonal (h-BN), zincblende (c-BN), wurtzite (w-BN), rhombohedral (r-BN), etc. Among them, the polytype of best known and of commonly synthesized is hexagonal, while that of electrically versatile is zincblende (usually termed cubic). The phase diagram of BNs has been established by Wentorf, Corrigan, and Bundy [1,2]. No doubt is that the /r-phase is the most stable at high temperatures, i.e, above 1500 °C. At the high temperature regime, the c-phase is stable only at very high pressures. As temperature is lowered, the transition pressure between the h-and c-phase goes down. Ambiguity exits about the phase boundary around the normal conditions.
