Density of States Effective Mass for p-Type Mg2Si-Mg2Sn Solid Solutions: Comparison between Experiments and First-Principles Calculations

Abstract

Tailoring and further optimization of thermoelectric materials requires detailed knowledge and understanding of the thermal and electrical transport in these materials. One crucial parameter is the density of states effective mass, which governs both the electrical conductivity as well as the Seebeck coefficient. We investigate the density of states effective mass for magnesium silicide, magnesium stannide and their solid solutions using experimental data as well as density functional theory in a generalized gradient approach; for the solid solutions, the special quasi-random structures approach is employed. Extracting the effective mass directly from the calculated densities of states, we can show an approximatively linear decrease from Mg2Si to Mg2Sn and consistency with respect to the chosen cell size. The experimental data, obtained by assuming a single parabolic band model, show good agreement with the calculated data for Mg2Sn and Sn-rich solid solutions, but a clear difference at the Si-rich side. The lower effective mass for the Sn-rich solid solutions indicates that the electronic properties are expected to be superior to those of Si-rich solid solutions as long as minority carrier effects can be neglected.