Electronic, elastic properties and hardness of the novel tetragonal silicon

Silicon is an important material for technical applications. Recently, a long-puzzling metastable phase of silicon (T-12-Si) has been theoretically identified. In this work, we used first-principles calculations to study the electronic and elastic properties and the hardness of this new silicon allotrope to enrich the relevant information. These properties of cubic Si (c-Si) were also calculated for comparison. The results show that the T-12-Si is mechanically anisotropic and has a lower bulk modulus and shear modulus than c-Si. Its theoretical hardness is 10.3 GPa, smaller than the value of 13.5 GPa for c-Si. Analyses of the electronic properties reveal that T-12-Si is an indirect band gap crystal with a gap value of 0.69 eV, making it a promising semiconductor for future technical applications and that covalent sp (3)-hybridization is the main interaction in this crystal. The reason the calculated hardnesses of c-Si and T-12-Si are rather small compared to that of diamond is also discussed.