ICT2014 Abstracts

The structural and thermoelectric properties of Al- and Sb-doped n-type Mg₂Si are examined using a first-principles calculation method. Mg₂Si has been attracting considerable attention as a promising thermoelectric material since it possesses attributes that are advantageous for practical applications in terms of cost and environmental protection: it is nontoxic, cheap, and composed of elements abundant in the Earth’s crust. Impurity doping is a well-established method for improving the thermoelectric performance of Mg₂Si. Sb is known to be an effective dopant for this material, and Al is also a promising candidate in terms of stability and environmental benignity[1]. Typical thermoelectric devices operating at elevated temperatures require that the impurity elements be highly stable. Therefore, fundamental understanding of the effect of impurity doping on thermoelectric properties and stability will enable us to provide theoretical guidelines for further development of Mg₂Si-based materials. To this end, we theoretically investigate the electronic structure, energetic stability, and the Seebeck coefficient of anti-fluorite Mg₂Si doped with Sb, Al, and Sb+Al. First, we carry out the lattice relaxation to determine the lattice constant and the atom positions of the impurity-doped systems by DFT simulation. We also discuss site preferences of the dopants and their energetic stability using the total energy calculations. Next, we calculate the electronic structure using the full-potential linearized augmented plane-wave method based on the local density approximation within density functional theory and the Seebeck coefficient using the Bloch–Boltzmann Equation. Our calculations indicate that the effect of the impurity doping on the thermoelectric properties are predominantly related to the site preferences of dopants and not strongly dependent on the structural changes induced by the impurity doping. 

[1] Y. Oto, T. Iida. T. Sakamoto, R. Miyahara, A. Natsui, K. Nishio, Y. Kogo, N. Hirayama, and Y. Takanashi, Phys. Status Solidi C 10, 1857-1861 (2013)