Mg_(2)Sn机械性质及热电输运性能的第一性原理计算

Mechanical Properties and Thermoelectric Transport Performance of Mg_(2)Sn from First-Principle Calculations

窄带隙半导体材料Mg_(2)Sn具有丰度大、密度低、无毒及环境友好等特点,是中低温热电材料的优秀候选者。本文基于密度泛函理论,结合不同形式的电子交换关联能系统分析了Mg_(2)Sn晶体的弹性系数、声子振动谱和电子能带结构,并基于非平衡玻尔兹曼输运理论计算了Mg_(2)Sn的热电性能。结果表明,GGA-PBE作为电子交换关联能可以很好地拟合立方相Mg_(2)Sn的力学性能(声子振动谱无虚频率),其体弹性模量为42.1 GPa且各向同性。同时,当工作温度高于300 K,Mg_(2)Sn的德拜温度开始趋于平缓且不高于315 K,表明Mg_(2)Sn在该温度区域内具有低声子热导率。使用B3LYP作为电子交换关联能可以估算Mg_(2)Sn费米能级附近的电子结构,发现价带顶附近存在三重简并态。同时计算结果表明,Mg_(2)Sn p型掺杂下的热电优值(ZT值)优于n型掺杂,可达1.05。本研究结果为进一步优化Mg_(2)Sn热电性能的研究提供借鉴。

The narrow-band gap semiconductor Mg_(2)Sn is an excellent candidate for medium and low temperature thermoelectric materials due to its high abundance,low density,non-toxicity and environmental friendliness.Based on density functional theory,the elastic coefficient,phonon vibration spectrum and electron band structure of Mg_(2)Sn crystal were systematically analyzed in combination with different forms of electron exchange correlation energy in this paper.The thermoelectric properties of Mg_(2)Sn were also calculated based on the non-equilibrium Boltzmann transport theory.The results show that GGA-PBE as the electron exchange correlation energy can well fit the mechanical properties of Mg_(2)Sn in cubic,when the phonon vibration spectrum has no virtual frequency,and the bulk elastic modulus of Mg_(2)Sn in cubic is 42.1 GPa and isotropic.Mg_(2)Sn has low phonon thermal conductivity due to the fact that the Debye temperature curve of Mg_(2)Sn tends to flat and no higher than 315 K in the test temperature region above 300 K.The electronic structure near the Fermi level of Mg_(2)Sn can be estimated by using B3LYP as the electron exchange correlation energy,and triple degeneracy states are found near the top of the valence band.Then,the results of the thermoelectric optimal value(ZT value)present that p-type doping Mg_(2)Sn is better than that of n-type doping,which can reach 1.05.The results of this study provide theoretical basis for further improving the thermoelectric properties of Mg_(2)Sn.