摘要:
热电材料是一类能够实现热与电相互转换的功能材料,在制冷和发电领域极具应用潜力.本文采用金属Sb元素非等电子替换Cu3Ga5Te9化学式中的Cu和Te,观察到材料Seebeck系数和电导率提升的现象.这些电学性能的改善与载流子浓度和有效质量的增大及迁移率基本维持不变有关.载流子浓度的提高是由于Sb原子占位在Te晶格位置后费米能级进入到价带所产生的空穴掺杂效应所致,同时也与Cu含量减少后铜空位(V-1Cu)浓度增大相关联.另外,非等电子替换后,阴离子(Te2-)移位导致了晶格结构缺陷参数u和η的改变,其改变量?u和?η与材料晶格热导率(κL )的变化密切相关.在766 K时,适量的Sb替换量使材料的最大热电优值(ZT)达到0.6,比Cu3Ga5Te9提高了近25%.因此,通过选择替换元素、被替换元素及替换量有效地调控了材料的电学及热学性能,在黄铜矿结构半导体中实现了非等电子元素替换改善热电性能的思想.
Abstract:
Thermoelectric materials, which allow the conversion between heat and electricity, can be directly applied in the fields of cooling and power generation. Here we report an effective approach: non-isoelectronic substitution of Sb for Cu and Te in Cu3Ga5Te9 to increase the Seebeck coefficient and electrical conductivity. This improvement is attributed to the enhancement in carrier concentration n and effective mass as well as the conservation of the carrier mobility μ. The enhancement of the carrier concentration is caused by the hole doping effect due to the drop of the Fermi level into the valence band when Sb occupies the Te lattice sites, and also due to the increase of the copper vacancy (V-1Cu ) concentration when Cu content decreases. In addition, the non-isoelectronic substitution can yield extra crystal structure defects. These defects, which are represented by the alterations of anion (Te2-) position displacement (u) and tetragonal deformation (η), directly govern the lattice thermal conductivity (κL) on an atomic scale. The maximum ZT value is 0.6 at 766 K with proper Sb substitution, which is about 25% higher than that of Cu3Ga5Te9. Therefore, we are able to effectively manipulate the electrical and thermal properties through proper selections of the substituting /substituted elements and their quantities, and prove that the non-isoelectronic substitution approach in the chalcopyrite semiconductors is an effective way to improve the thermoelectric performance.
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