Electronic structure and optical properties of ZnSiO3 and Zn2SiO4

The electronic structure and optical properties of orthorhombic, monoclinic, and rhombohedral (corundum type) modifications of ZnSiO3, and of rhombohedral, tetragonal, and cubic (spinel type) modifications of Zn2SiO4 have been studied using ab initio density functional theory calculations. The calculated fundamental band gaps for the different polymorphs and compounds are in the range 2.22-4.18 eV. The lowest conduction band is well dispersive similar to that found for transparent conducting oxides such as ZnO. This band is mainly contributed by Zn 4s electrons. The carrier effective masses were calculated and compared with those for ZnO. The topmost valence band is much less dispersive and contributed by O 2p and Zn 3d electrons. From the analysis of charge density, charges residing in each site, and electron localization function, it is found that ionic bonding is mainly ruling in these compounds. The calculated optical dielectric tensors show that the optical properties of ZnSiO3 and Zn2SiO4 are almost isotropic in the visible part of the solar spectra and depend negligibly on the crystal structure. Within the 0-4 eV photon energy range, the calculated magnitude of the absorption coefficient, reflectivity, refractive index, and extinction coefficient are smaller than 10(3) cm(-1), 0.15, 2.2, and 0.3, respectively, for all the ZnSiO3 and Zn2SiO4 phases considered in this work. This suggests that zinc silicates can be used as antireflection coatings.