Komisarchik G, Gelbstein Y, Fuks D
Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
Phys Chem Chem Phys. 2016 Nov 30;18(47):32429-32437. doi: 10.1039/c6cp06364k.
Lead telluride based compounds are of great interest due to their enhanced thermoelectric transport properties. Nevertheless, the donor type impurities in this class of materials are currently mainly limited and alternative types of donor impurities are still required for optimizing the thermoelectric performance. In the current research titanium as a donor impurity in PbTe is examined. Although titanium is known to form resonant levels above the conduction band in PbTe, it does not enhance the thermo-power beyond the classical predictions. Recent experiments showed that alloying with a small amount of Ti (∼0.1 at%) gives a significant increase in the figure of merit. In the current research ab initio calculations were applied in order to correlate the reported experimental results with a thermoelectric optimization model. It was found that a Ti concentration of ∼1.4 at% in the Pb sublattice is expected to maximize the thermoelectric power factor. Using a statistical thermodynamic approach and in agreement with the previously reported appearance of a secondary intermetallic phase, the actual Ti solubility limit in PbTe is found to be ∼0.3 at%. Based on the proposed model, the mechanism for the formation of the previously observed secondary phase is attributed to phase separation reactions, characterized by a positive enthalpy of formation in the system. With extrapolation of the obtained ab initio results, it is demonstrated that lower Ti-doping concentrations than previously experimentally reported ones are expected to provide power factor values close to the maximal one, making doping with Ti a promising opportunity for the generation of highly efficient n-type PbTe-based thermoelectric materials.
碲化铅基化合物因其增强的热电输运性能而备受关注。然而，这类材料中的施主型杂质目前主要受到限制，仍需要替代类型的施主杂质来优化热电性能。在当前的研究中，对碲化铅中作为施主杂质的钛进行了研究。尽管已知钛在碲化铅的导带上方形成共振能级，但它并没有使热功率超过经典预测值。最近的实验表明，与少量钛（约0.1原子%）合金化可使优值显著提高。在当前的研究中，应用了从头算计算，以便将报道的实验结果与热电优化模型相关联。结果发现，在铅亚晶格中钛浓度约为1.4原子%时，有望使热电功率因子最大化。使用统计热力学方法并与先前报道的二次金属间相的出现相一致，发现碲化铅中钛的实际溶解度极限约为0.3原子%。基于所提出的模型，先前观察到的二次相的形成机制归因于相分离反应，其特征是系统中形成焓为正。通过对获得的从头算结果进行外推，证明比先前实验报道的更低的钛掺杂浓度有望提供接近最大值的功率因子值，这使得用钛掺杂成为生成高效n型碲化铅基热电材料的一个有前景的机会。
