Abstract
Thermal phase stability of rhombohedra] boron nitride has been studied between 0 and 8 GPa from 300 to 2700 K. Analysis of the data obtained points to the decisive role of kinetic factors in the rBN phase transformations, the structure and dispersity of the samples under study being of great importance. rBN phase transformations in the cBN thermodynamic stability region of the equilibrium p,T phase diagram for boron nitride occur according to Ostwald stepwise principle by the rBN→hBN→(wBN)→cBN scheme.