Elastic constants of AlB2-type compounds from first-principles calculations

Elastic constants (Cij’s) of 24 compounds in the AlB2-type diborides have been calculated by first-principles with the generalized gradient approximation and compared with the available experimental data. Values of all independent elastic constants as well as bulk modulus in a and c directions (Ba and Bc, respectively) were predicted. The elastic modulus of the AlB2-type compounds were calculated according to the theoretical elastic constants by Voigt–Reuss–Hill averaging scheme. Ductility and anisotropy in these compounds were further analyzed based on their B/G ratio and elastic constants. It is founded that AlB2 is more ductile while ScB2 is more brittle, and AlB2 has a highest elastic anisotropy in the 24 AlB2-type compounds.