Pressure-induced semiconductor-to-metal transition in Mg₂Sn with the modified Becke-Johnson potential

Department of Physics, School of Sciences, China University of Mining and Technology Xuzhou 221116, Jiangsu, China

^(a) guosd@cumt.edu.cn

Received: 2 December 2014
Accepted: 18 February 2015

Abstract

We investigate the energy band gap, dielectric functions and thermoelectric properties of Mg₂Sn at hydrostatic pressure by using a modified Becke and Johnson exchange potential. It is very interesting that the energy band gap first increases with increasing pressure, and then decreases. The phonon calculations prove that no structural phase transition under the considered pressure is produced. When the pressure reaches 5.6 GPa, the energy band gap attains the biggest value, which is also a critical pressure with the Mg s-character near the high symmetry X-point transforming from the first conduction band to the second one. When the pressure increases to 50.7 GPa, the energy band gap closes, leading to a semiconductor-to-semimetal transition. As the pressure increases, the main peaks of the real and imaginary part of the dielectric functions of Mg₂Sn move toward the high-energy region. The Seebeck coefficient and power factor for p-type doping change little with increasing pressure, but for n-type they vary greatly. The change trend of the Seebeck coefficient and power factor for n-type doping as a function of pressure is conic, whose critical pressure is just 5.6 GPa.