Mg3Bi2热电性质的第一性原理研究

FIRST-PRINCIPLES STUDY OF THE THERMOELECTRIC PROPERTIES OF Mg3Bi2

肖作为

11849418

硕士

物理学

黄丽

2020-05-29

2020-07-07

哈尔滨工业大学

深圳

热电材料作为新型能源材料，拥有极好的应用前景，归因于它具有环境友好性，可再生和可重复利用等优良特性。唯一限制热电材料大规模投入实际应用的因素是其转化功率较传统能源材料低很多，通常不超过15%。因此，提高热电材料的转化效率是热电材料研究领域的重要目标。值得注意的是，Mg3Bi2在费米面附近的导带中具有多能谷特征，展现了其作为优秀热电材料的潜力。一个材料的热电性能由一个无量纲参数热电优值ZT来描述。构成ZT的输运参数有塞贝克系数S，电导率σ和热导率к，其中热导率又分为电子热导率与晶格热导率，通常电子热导率与晶格热导率相比所占比例很小，因此不进行考虑。此时，与电子相关的部分由功率因数来描述。除此之外，输运参数之间彼此相互影响，无法独立调整某一个参数，因此，对ZT的调整是一个复杂的需要反复尝试的过程。本文通过第一性原理计算，对Mg3Bi2的基态性质及其在低静水压力条件下的热电性质进行了研究。通过杂化泛函方法计算获得的基态电子结构性质，显示其为窄带半导体，能隙为0.15 eV。同时，导带底位于倒空间高对称线以外的位置。对体系施加静水压力,从1 GPa一直增加到4 GPa，声子谱中无虚频出现，表明加压过程中结构始终稳定。随着压力增大，能隙逐渐变宽，导带中出现能带收敛现象。在300 K的温度下，当N型掺杂的载流子浓度处于1019-1020 cm-3之间时，体系的功率因数随着压力的增大而逐渐变大，并达到最大值。由此可知，对Mg3Bi2进行N型掺杂，并在低压的调控下，热电性能逐渐变好。

Thermoeletric materials have excellent application prospects as one of new energy materials, which is attributed to their superb characteristics of being environmentally friendly, renewable and reusable. The only factor limiting the large-scale implementation of thermoelectric materials in practice is that their conversion power is much lower than traditional energy sources, usually not exceeding 15%. Therefore, the improvement of the conversion efficiency of thermoelectric materials is an essential goal in the field of thermoelectric materials research. It is worth nothing that Mg3Bi2 has a multi-valley feature in the conduction band near the Fermi surface, demonstrating its potential as an excellent thermoelectric material. The thermoelectric performance of a substance is described by a dimensionless parameter thermoelectric figure of merit ZT. The transport parameters constituting ZT are Seebeck coefficient S, electrical conductivity σ and thermal conductivity к. Thermal conductivity is divided into electronic thermal conductivity and lattice thermal conductivity. Usually, the ratio of electronic conductivity to lattice thermal conductivity is minimal compared, and it can be ignored. At this point, the electron-related part is represented by the power factor. Besides, the transport parameters interact with each other and cannot be adjusted independently for a particular parameter. Therefore, the adjustment of ZT is a complicated process that requires repeated trial and error.In this thesis, the ground state properties of Mg3Bi2 and its thermoelectric properties under low-pressure conditions are studied through first-principles calculations. The ground-state electronic structure information, calculated by the Hybrid functionals method shows that it is a narrow-band semiconductor with an energy gap of 0.15 eV. The bottom of the conduction band is located outside the high symmetrical line in the reciprocal space. The hydrostatic pressure that applied to system ranges from 1 GPa to 4 GPa, and there is no virtual frequency in the phonon spectrum, which indicates that the structure remains stable during the pressurization process. As the pressure increases, the energy gap gradually widens, and band convergence occurs in the conduction band. At a temperature of 300K, when the carrier concentration of N-type doping is between 1019-1020 cm-3, the power factor of the system gradually increases with increasing pressure and reaches a maximum. It can be seen that the thermoelectric performance of the N-doping of Mg3Bi2 with low-pressure modulation leads to progressively better thermoelectric performance.

热电优值 第一性原理计算 电子结构

thermoelectric figure of merit first-principles calculation electronic structure

中文

联合培养

南方科技大学

肖作为. Mg3Bi2热电性质的第一性原理研究[D]. 深圳. 哈尔滨工业大学,2020.