Equation of state of cubic boron nitride at high pressures and temperatures

We report accurate measurements of the equation of state (EOS) of cubic boron nitride by x-ray diffraction up to 160 GPa at 295 K and 80 GPa in the range 500-900 K. Experiments were performed on single crystals embedded in a quasihydrostatic pressure medium (helium or neon). Comparison between the present EOS data at 295 K and literature allows us to critically review the recent calibrations of the ruby standard. The full P-V-T data set can be represented by a Mie-Gruneisen model, which enables us to extract all relevant thermodynamic parameters: bulk modulus and its first pressure derivative, thermal expansion coefficient, and thermal Gruneisen parameter and its volume dependence. This equation of state is used to determine the isothermal Gruneisen mode parameter of the Raman TO band. A formulation of the pressure scale based on this Raman mode, using physically constrained parameters, is deduced.