Electronic and Transport Properties of Sr doped Mg2Si Thermoelectric Material

Abstract

We investigated the electronic structure, dynamic stability, optical, and thermoelectric properties of strontium doped Mg2−x SiSrx, x = 0, 1, using First Principle approach with ultra-soft pseudopotential method to treat the interaction between the valence electron and the ion core and the Generalized Gradient Approximation (GGA) in Perdex Burke Emzerhof (PBE) form is used to process the exchange-related energy function. Sr modified Mg2Si show good agreement with the experimental result for the electronic and thermoelectric properties. With semiclassical Boltzmann transport theory, the transport properties of Mg2Si and Sr doped Mg2Si alloys have been investigated systematically. The result of DFT conformed that, the undoped Mg2Si system has indirect energy gap to a value of 0.222 eV; Sr doped 2x1x1 Mg2Si supercell, showing direct bandgap with a value of 0.195 eV. The carrier concentration of Sr doped Mg2Si thermoelectric material increased. After the doping, the fermi level shifts towards the conduction band and comprises of via a strong hybridization between the Sr-s, Si-p, Mg-s, and Mg-p orbitals, indicating that the covalent bonds formed by Sr, Si, and Mg atoms is very strong. The electrical conductivity of Sr doped Mg2Si material is due to electrons, which is justified from the negative value of the Seebeck coefficient and its value increases with temperature. The lattice thermal conductivity dominates the electronic thermal conductivity as a function of temperature for Sr doped Mg2Si system. In this work, the Sr-doped Mg2Si materials were found to be a better thermoelectric material with increased Seebeck coefficient, electrical conductivity, and corresponding electronic thermal conductivity at a high-temperature range.