Study of thermodynamic properties and elastic constants of cubic boron nitride by statistical moment method

The statistical moment method has been applied to investigate temperature effects on the thermodynamic and elastic properties of the cubic boron nitride (cBN). The analytical expressions of thermal-induced atomic displacement, the mean-square displacement, elastic constants (Young's modulus, bulk modulus, shear modulus, and longitudinal-wave elastic constant), and the bulk and longitudinal sound velocities of cBN compound have been derived. Our theoretical calculations are compared with previous experiments and computations showing reasonable agreement. We have shown that while the mechanical strength and Debye temperature of the cBN material are slightly reduced as temperature rises, the mean-square displacement function increases rapidly. The noticeable difference in mean-square displacements of B isotopes is observed at low temperature, and the disparity diminishes gradually at high temperatures. The calculations of the present work can be used as an appropriate reference for the future experiments.