The elastic anisotropy, electronic and optical properties of Bi4Si3O12, Bi2SiO5, Bi12SiO20 and Bi2Si3O9 crystals from first-principles calculations

Bismuth silicates are the excellent semiconductor materials with excellent physical and chemical properties. In this paper, the physical properties of four Bi-Si-O crystals such as orhorhombic Bi2SiO5, hexagonal Bi2Si3O9, cubic Bi4Si3O12 and cubic Bi12SiO20 were studied using the first-principles calculations. The research contents include the elastic anisotropy, electronic properties and optical properties of Bi-Si-O crystals. Bi2Si3O9 crystal has the good compressive property. The hexagonal Bi2Si3O9 show the ductile properties, but the other Bi-Si-O materials have the brittle characteristics. In addition, the elastic hardness indicates that all the materials have the relatively low hardness. Their elastic anisotropy was evaluated as follows: orthorhombic Bi2SiO5 > hexagonal Bi2Si3O9 > cubic Bi4Si3O12 > cubic Bi12SiO20. The electronic properties are analyzed in details. The band gap widths of Bi2SiO5, Bi2Si3O9, Bi4Si3O12 and Bi12SiO20 are 2.775 eV, 3.454 eV, 3.997 eV and 2.256 eV respectively. For the static optical anisotropy, the dielectric constants and the related parameters of the above substances are analyzed.