摘要
作为最具潜质的中温区热电材料之一,Mg 2Si 1-x Sn x基合金由于其低廉的成本和无毒无害等优点,在过去十几年受到广泛关注。Si和Sn原子间具有较大的质量差,有利于声子的合金化散射,使得晶格热导率极大降低(可达到1.8 W·m-1·K-1),解决了二元Mg 2Sn合金热导率较高的问题。大多数Mg 2Si 1-x Sn x合金通过降低晶粒尺寸来进一步降低晶格热导率,从而优化热电性能,然而,这类材料制备的热电器件在高温服役过程中容易出现由于晶粒长大导致的性能降低。因此,通过提高功率因子,如掺杂、能带工程等方法,来优化热电性能是更加可靠的路径。本工作采用第一性原理计算方法,对不同Sn成分的Mg 2Si 1-x Sn x(0.25≤x≤0.75)固溶体进行电子结构分析和热电性能预测。结果表明,在x=0.625时产生了能带收敛效应,可以在不影响电导率的前提下有效提高Seebeck系数值。计算预测的Seebeck系数在掺杂浓度为3×1020 cm-3时取得最大值-246μV·K-1,功率因子最高可达6.2 mW·m-1·K-2,不同温度下的Seebeck系数和电导率预测结果与高温度梯度定向凝固试样测试所得的结果拟合较好。根据测试所得的热导率结果,在T=700 K处计算预测的最大ZT值为1.3,而实验测试值为1.16,同时,在中温区550~800 K之间预测和实验测试的ZT值分别可以保持在1.0和0.9以上。因此,通过优化功率因子的方法可以有效提高Mg 2Si 1-x Sn x晶体的热电性能,为此类热电材料的性能优化提供了新的思路。
As one of the most potential medium temperature thermoelectric materials,Mg2Si1-xSnx-based alloy has received widely attention due to the advantage of low cost and non-toxic. Lattice thermal conductivity of ternary Mg2Si1-xSnxalloys is reduced,because alloying scattering is enhanced by the large mass difference of elements. The minimum of thermal conductivity is 1. 8 W·m-1·K-1,and it well resolves the disadvantage of high thermal conductivity for Mg2Sn binary alloys. However,the main methods to optimize the thermoelectric properties of Mg2Si1-xSnxalloys are decreasing the grain size to further reduce the thermal conductivity. But the performance of this kind of thermoelectric device is prone to degradation due to the grain growth in high temperature service. Therefore,improving the power factor by the method of doping and band engineering is a more reliable way to optimize the thermoelectric performance. In this paper,electronic structures analysis and thermoelectric properties prediction has been made to the Mg2Si1-xSnx( 0. 25≤x≤0. 75) compounds by first principle calculation method. The calculated band structures in Mg2Si1-xSnxshow the conduction band convergence directly. This convergence in energy at x = 0. 625 can enhance the Seebeck coefficient of the solid solution without influencing the electrical conductivity. The Seebeck coefficient and power factor of Mg2Si0. 375Sn0. 625 could reach-246 μV·KZ-1 and 6. 2 mW·m-1·K-2,respectively,at the optimal doping density of 3×1020 cm-3. The predicted and tested results of ZT maximum are 1. 3 and 1. 16 at T = 700 K,respectively. In the medium temperature range of 550-800 K,the predicted and tested ZT values can keep above 1. 0 and 0. 9,respectively. Therefore,power factor optimization is an effective way to improve the thermoelectric properties of Mg2Si1-xSnx crystal.
作者
李鑫
谢辉
魏鑫
张亚龙
LI Xin;XIE Hui;WEI Xin;ZHANG Yalong(School of Materials Engineering,Xi’an Aeronautical University,Xi’an 710077,China)
出处
《材料导报》
EI
CAS
CSCD
北大核心
2020年第18期18098-18103,共6页
Materials Reports
基金
国家自然科学基金委青年项目(51904219)
西安航空学院校级科研基金项目(2019KY0203)。
关键词
第一性原理计算
Mg
2Si
1-
X
SN
X
热电性能
定向凝固
first principle calculation
Mg 2Si 1-x Sn x
thermoelectric properties
directional solidification
作者简介
李鑫,2018年6月毕业于西北工业大学材料学院,获得工学博士学位。现为西安航空学院材料工程学院讲师。目前主要研究领域为定向凝固、热电材料和第一性原理计算。lixin005@xaau.edu.cn。
