Semiempirical formulae for elastic moduli and brittleness of diamondlike and zinc-blende covalent crystals

In the present work, semiempirical formulae for both bulk B and shear G moduli of diamondlike and zinc-blende covalent crystals are elaborated in terms of bond length and ionicity fraction of the bonding. The resulting expressions can be applied to a broad selection of covalent materials and their modulus predictions are in good agreement with the experimental data and those from ab initio calculations. Furthermore, the correlation between the ratio G/B and the aforementioned bonding parameters was investigated. The analysis of this relationship demonstrates that compared to the ionicity fraction, the bond length is the predominant parameter responsible for the brittle features of covalent materials