Thermal equation of state of cubic boron nitride: Implications for a high-temperature pressure scale

Abstract

The equation of state of cubic boron nitride (cBN) has been determined to a maximum temperature of $3300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at a simultaneous static pressure of up to more than $70\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Ab initio calculations to $80\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $2000\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ have also been performed. Our experimental data can be reconciled with theoretical results and with the known thermal expansion at $1\phantom{\rule{0.3em}{0ex}}\text{bar}$ if we assume a small increase in pressure during heating relative to that measured at ambient temperature. The present data combined with the Raman measurements we presented earlier form the basis of a high-temperature pressure scale that is good to at least $3300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.