Ab initio calculations of the relationship between the alpha alumina toughness and its electronic structure under pressure

We investigated the alumina electronic structure, the elastic properties under different pressure and its toughness. The calculations were performed using the ab initio pseudopotential method, in which we employed the Perdew–Wang form of the generalized gradient approximation (GGA) together with plane wave basis sets for expanding the periodic electron density. The states at the Fermi level are mainly composed of Al-3s, Al-3p and O-2p orbital, which demonstrate the hybridization between Al and O atoms in alpha alumina. Our results show that there exists covalence besides ionicity in alumina. The covalence results in the delocalization of the electrons. The delocalization improved as the pressure contributes to the toughness of alumina. According to the quotient of bulk to shear modulus, we know alpha alumina is brittle in nature at ambient conditions. But the quotient exhibits the increasing tendency with pressure. At 100 GPa, the ratio is up to 2.0 which is larger than the critical value 1.75. We find that it is possible to improve the toughness of alpha alumina at high pressure (100 GPa). The aim of the work is to understand the influence of pressure on the alpha-Al2O3 electronic structure and the toughness.