Correlation between hardness and elastic moduli of the covalent crystals

From a statistical manner, we collected and correlated experimental bulk (B), shear (G), Young's modulus (E), and ductility (G/B) with Vickers hardness (H(v)) for a number of covalent materials and fitted quantitative and simple H(v)-G and H(v)-E relationships. Using these experimental formulas and our first-principles calculations, we further predicted the microhardness of some novel potential hard/superhard covalent compounds (BC(2)N, AlMgB(14), TiO(2), ReC, and PtN(2)). It was found that none of them are superhard materials (H(v) >= 40 GPa) except BC(2)N. The present empirical formula builds up a bridge between Vickers hardness and first-principles calculations that is useful to evaluate and design promising hard/superhard materials. (C) 2011 Elsevier B.V. All rights reserved.