A Comparative Study of the Effect of Strain on the Electronic and Optical Properties of Filled and Unfilled Ba8Si46 Type I-clathrate

A first principles calculations study is carried out to theoretically investigate the effect of compressive and tensile strains on the structural, electronic and optical properties of type-I guest-free Si-46 and barium-filled Ba8Si46 clathrates. The electronic band structure of the unfilled Si-46 clathrate revealed a semiconducting behaviour with a quasi-direct band gap of 1.36 eV. Under hydrostatic pressure, the bandgap magnitude of the guest-free Si-46 behaves monotonously. For the Ba doped Si-46 clathrate (Ba8Si46) structure, the strain has no significant effect on the electronic band structure, while its impact on the optical properties is appreciable. The optical properties, such as the dielectric function and the absorption were computed for different strain variations, which are clearly enhanced for both the unfilled Si-46 and Ba-filled Ba8Si46 clathrates when the pressure is 1 GPa in the direction of a compressive state.