Lattice parameters of hexagonal and cubic boron nitrides at high temperature and high pressure

The lattice parameters of hBN and cBN at a range of the synthetic temperature and pressure (1200∼2100K, 4.0∼8.0GPa) were calculated using ab initio density-functional theory. Lattice parameters a of hBN and cBN calculated by theoretical methods, were in good agreements with the experimental results, with the maximum relative difference being 2.50% and 1.53%, respectively. Meanwhile, the maximum relative difference of lattice parameters c of hBN in theoretical method was 7.53%, which was also reasonably consistent with the experimental results. It was found that the lattice parameters of hBN and cBN increased slowly with temperature, but decreased rapidly with pressure.