To better understand the thermoelectric efficiency of the Mg-based thermoelectrics, using hybrid density-functional theory, we study the microscopic origins of valley degeneracies in the conduction band of the solid solution Mg2Si1-xSnx and its constituent components - namely, Mg2Si and Mg2Sn. In the solid solution of Mg2Si1-xSnx, the sublattices are expected to undergo either tensile or compressive strain in the light of Vegard's law. Interestingly, we find both tensile strain of Mg2Si and compressive strain of Mg2Sn enhance the conduction band valley degeneracy. We suggest that the optimal sublattice strain as one of the origins of the enhanced Seebeck coefficient in the Mg2Si1-xSnx system. In order to visualize the enhanced band valley degeneracy at elevated temperatures, the ground state eigenvalues and weights are projected by convolution functions that account for high temperature effects. Our results provide theoretical evidences for the role of sublattice strain in the band valley degeneracy observed in Mg2Si1-xSnx.
Bibliographical noteFunding Information:
We gratefully acknowledge support from the Basic Science Research Program by the NRF, (Grant No. 2014R1A1A1003415) and the Australian Research Council (ARC). This work was also supported by the third Stage of Brain Korea 21 Plus Project Division of Creative Materials. Computational resources have been provided by the Australian National Computational Infrastructure (NCI) and by the KISTI supercomputing center (KSC-2015-C3-009).
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All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry