Mg2Si化合物在静水压下的电子输运性能研究

本文基于第一性原理采用全电势线性缀加平面波方法和波尔兹曼理论运算了在静水压下Mg₂Si的电子和热电性能. 研究发现, 对于n型载流子控制Mg₂Si输运性质, 应变达到0.02时, 室温情况下, 热电性能参数得到了明显提高, 其塞贝克系数增幅为26%, 功率因数增幅47%; 高温时, 功率因数增幅45%. 而对于主要载流子为空穴时, 其热电系数最值出现在应变为0.01时. 但其数值与未施加静水压的结构相比提高不多, 表明对于p型Mg₂Si半导体应变对其输运性能的影响不大. 并且结合电子能带结构图解释这些现象.

Electron transport properties of Mg2Si under hydrostatic pressures

The electronic and thermoelectric properties of Mg₂Si under hydrostatic pressures have been investigated using the first principles calculations with general potential linearized augmented plane-wave method and the semiclassical Boltzmann theory with the rigid band approach and the constant scattering time relaxation approximation. In this work, the hydrostatic pressure is simulated by applying equiaxial strain method for the cubic anti-fluorite structure of Mg₂Si in space group Fm3m. The strain values ranging from -0.03 to 0.03 describe the compressive and tensile Processes under pressure. The band structure, electrical conductivity, Seebeck coefficient and power factor have been calculated and analyzed in detail.#br#From the band structure in Mg₂Si one can see that the bottom of the conduction band shows significant changes under strains. Especially, when the strain is up to 0.02, there are two twofold-degeneracy states occurring at the center of the Brillouin zone. The top of the valence band shows a slight change due to the strain effect. For the unstrained structure, our calculated thermoelectric data are in accordance with other reports. Moreover, the results indicate that when the value of strain is up to 0.02, the transport properties get an optimal functioning of Mg₂Si due to electron doping. At 300 K, the Seebeck coefficient improves obviously and comes up to 126%. And the power factor is up to 47% (45%) at T=300 K (700 K). Consequently, the thermoelectric properties can be improved through applying negative pressures to the Mg₂Si crystal. For the case of hole doping, the transport parameters change obviously at a small strain value, and change gently at a high strain values. When the strain is up to 0.01, the Seebeck coefficient reaches the maximum value 439 μV/K^-1. But, the power factor only increases 0.9%–2%. Hence, we can conclude that the hydrostatic pressures have a slight influence on the thermoelectric properties of hole-doped materials.