Elasticity of cubic boron nitride under ambient conditions

As a superhard material with properties similar to diamond including chemical inertness, cubic boron nitride (cBN) is an excellent candidate as a pressure calibration standard for high-temperature high-pressure research using its pressure-volume-temperature (P-V-T) equation of state. However, the elastic properties of cBN at ambient conditions reported in the literature vary by up to 8, which can likely be attributed in part to variability in the cBN composition and defect structure and measurement uncertainties. We have measured the single-crystal elastic moduli of high-purity cBN with high precision by Brillouin scattering measurements, making an effort to minimize experimental uncertainties. We obtain values of C₁₁ 798.4 1.7 GPa, C₄₄ 469.0 1.0 GPa, and C₁₂ 172.4 1.1 GPa, from which the isotropic aggregate bulk modulus Ks 381.1 1.3 GPa and shear modulus G 398.8 1.2 GPa (the Hill average) were calculated. Our results improve the precision and reduce the uncertainties in the elastic moduli of high-purity cBN as a reference for future high P-T pressure scales.