Elastic constants of cubic and wurtzite boron nitrides

Nagakubo A., Ogi H., Sumiya H., et al. Elastic constants of cubic and wurtzite boron nitrides. Applied Physics Letters, 102(24), 241909 (2013) https://doi.org/10.1063/1.4811789.
We synthesized pure polycrystalline cubic boron nitride (cBN) and wurtzite boron nitride (wBN) by the direct conversion method from hexagonal boron nitride, and measured their longitudinal-wave elastic constants CL between 20 and 300 K using picosecond ultrasound spectroscopy. Their room-temperature values are 945 ± 3 GPa and 930 ± 18 GPa for cBN and wBN, respectively. The shear modulus G of cBN was also determined by combining resonance ultrasound spectroscopy and micromechanics calculation as G = 410 GPa. We performed ab-initio calculations and confirmed that the generalized gradient approximation potential fails to yield correct elastic constants, which indicated the necessity of a hybrid-functional method. © 2013 AIP Publishing LLC.