The parameters of equilibrium between oxygen solid solutions in cubic and graphite-like hexagonal boron nitrides

Abstract

Abstract A decrease in the onset temperature of the cBN-to-hBN solid-phase transformation with increase in the oxygen content of cBN samples has been found experimentally. This dependence might be attributable to the existence of oxygen solid solutions in cBN and hBN. From the experimental data and taking into account the kinetics of solid-phase transformations, the equilibrium onset temperature of the cBN-to-hBN transition has been derived for samples with different oxygen contents. In the framework of phenomenological thermodynamics, the model parameters have been determined and the lines of equilibrium between oxygen solid solutions in cubic and graphite-like hexagonal boron nitride have been calculated. It has been shown that a decrease in the oxygen content of the boron nitride–solvent system usually used for cBN synthesis should induce an increase in the thermodynamic stimulus to the hBN-to-cBN transformation at high pressures.