In this work, an attempt was made to employ the first-principles calculations in conjunction with the empirical approaches to predict and interpret the TE properties of the Mg2Si-based materials based on their doping levels and chemical compositions.
We calculated the electronic transport properties of Mg2Si with the BoltzTraP code which employs the semi-classical transport theory and the electronic structures derived from the first-principles calculations. In addition to the constant relaxation time approximation and the rigid band model, a temperature dependent band gap was used in the calculations. The results were compared to the previous experimental data dating back to 1950s. Though the calculations were based on the single crystal model, the temperature and doping level dependence of S and σ are generally reproduced for both single crystal and polycrystalline samples.
To evaluate the ZT values, we estimated the lattice thermal conductivity of the Sb-doped Mg2Si compounds using a classical model that includes the Debye approximation and considers the influence of the chemical compositions. The main trends of the results agree qualitatively with the experimental data.
Our work shows that it is possible to predict, at least qualitatively, the TE performance of the doped Mg2Si compounds in the relatively large temperature range and wide doping range by combing the first-principles calculations with the empirical models. It may be beneficial to the development of the Mg2Si-based thermoelectric generators by providing some guidance for tuning the doping level and composition of the materials.