Thermal Expansion of Hexagonal Boron Nitride

A heuristic model is proposed for the dependence with temperature of the linear coefficients of thermal expansion (TEC) of hexagonal boron nitride (hBN) parallel to the crystallographic a and c axes, namely and . The model proposed for the linear TECs of hBN is consistent with physical constraints at the low‐ and high‐temperature limits. The model's free parameters are determined by a multi‐objective fitting to literature data on lattice parameters and linear TECs versus temperature, as determined experimentally by X‐ray diffraction and interferometric techniques. For hBN, is negative up to 1290(170) K (more than twice the corresponding temperature for graphite), with a minimum of around 230 K. According to the calculations and literature data, the linear TEC should remain negative at least up to 9 GPa. Furthermore, the linear coefficient of thermal expansion should decrease with pressure as = .