Largely Enhanced Seebeck Coefficient and Thermoelectric Performance by the Distortion of Electronic Density of States in Ge2Sb2Te5
Largely Enhanced Seebeck Coefficient and Thermoelectric Performance by the Distortion of Electronic Density of States in Ge2Sb2Te5
复制标题
Ge2Sb2Te5 电子态密度畸变极大提高了塞贝克系数和热电性能
DOI：
10.1021/acsami.9b12854
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发表时间：
2019-09-18
影响因子：
9.5
通讯作者：
Chen, Lidong
中科院分区：
文献类型：
--
作者：
Hu, Ping;Wei, Tian-Ran;Chen, Lidong
作为最先进的相变材料之一，稳定的六方晶系化合物Ge_2Sb_2Te_5还具有良好的热电性能，具有高电导率和低热导率。然而，过高的载流子浓度和低塞贝克系数是实现高zT值的瓶颈。在这项工作中，与意图优化的电气性能，铟被引入作为一个潜在的施主在一系列的Ge 2-xInxSb 2 Te 5样品的掺杂剂。铟取代锗降低了空穴载流子的密度，提高了塞贝克系数。值得注意的是，掺杂样品的室温Seebeck系数可以是未掺杂样品的3倍，这明显偏离了基于单抛物带模型的理论预测的Pisarenko关系.通过密度泛函理论计算和模型模拟，认为Seebeck系数的显著提高是由于掺杂引起的电子态密度的局域畸变。进一步的观察表明，铟掺杂增强了邻近铟的Ge-Te的成键特性，并增强了沿c轴沿着的原子相互作用。由于优化的电性能以及抑制的热导率，在Ge 1.85 In 0.15 Sb 2 Te 5在700 K下实现了0.78的最大zT值，这比原始样品高约40%。
As one of the state-of-the-art phase-change materials, the stable Ge2Sb2Te5 hexagonal compound also exhibits decent thermoelectric performance with high electrical conductivity and low thermal conductivity. Nonetheless, the excessively high carrier concentration and low Seebeck coefficient are the bottlenecks to achieve high zT values. In this work, with the intention to optimize the electrical properties, indium was introduced as a potentially donor-like dopant in a series of Ge2-xInxSb2Te5 samples. The substitution of indium for germanium lowers the density of hole carriers and enhances the Seebeck coefficient. Noticeably, the room-temperature Seebeck coefficient of the doped samples can be three times as large as that of the pristine one, which obviously departures from the theoretically predicted Pisarenko relation based on the single parabolic band model. By virtue of DFT calculations and modeling, the remarkable enhancement of Seebeck coefficient was attributed to the doping-induced local distortion in the electronic density of states. Further insight reveals that indium doping amplifies the bonding character of Ge-Te adjacent to indium and enhances the atomic interaction along the c-axis. Due to the optimized electrical properties as well as the suppressed thermal conductivity, a maximal zT value of 0.78 was achieved in Ge1.85In0.15Sb2Te5 at 700 K, which is about 40% higher than that of the pristine sample.