Analyzing transport properties of p-type Mg2Si-Mg2Sn solid solutions: Optimization of thermoelectric performance and insight into the electronic band structure

Kurzfassung

We have synthesized the complete stoichiometric range of the p-Mg2Si1-xSnx striving for the optimization of the thermoelectric properties of p-type Mg2(Si, Sn) with respect to composition. The experimental data is analyzed in the framework of a single parabolic band (SPB) model and we can show that the thermoelectric properties can be well presented if acoustic phonon scattering and alloy scattering are taken into account. We find that the maximum achievable carrier concentration and power factor increase with higher Sn content. Also, the carrier mobility increases strongly from Mg2Si to Mg2Sn due to changing density of states effective mass for the valence band which decreases from m_(D )^* (〖Mg〗_2 Si)=2.2 m_0 to m_D^* (〖Mg〗_2 Sn)=1.1 m_0. Retrieval of the acoustic phonon scattering potential (E_Def=9 eV) and the alloy scattering parameter (E_AS=0.5 eV) allows modelling the thermoelectric properties for any arbitrary composition. Hence, we can predict the optimum zT for x ≈0.65-0.7 and the maximum power factor for Sn-rich compositions. We furthermore reveal that significant improvement of the thermoelectric properties of Si-rich compositions can be achieved by increasing the carrier concentration experimentally and that difference between n- and p-type Mg2(Si, Sn) is due to the disparity between the valence and the conduction bands and not the interaction potentials.