Gayner Chhatrasal, Natanzon Yuriy, Amouyal Yaron
Department of Materials Science and Engineering, Technion─Israel Institute of Technology, Haifa 32000, Israel.
ACS Appl Mater Interfaces. 2022 Jan 26;14(3):4035-4050. doi: 10.1021/acsami.1c20300. Epub 2022 Jan 10.
ZnO is a promising thermoelectric (TE) material for high-temperature applications; however, its TE performance is limited by strong coupling between electrical and thermal transport. In this study, we synthesized Al and Ti co-doped ZnO by a solid-state reaction and air sintering at 1500 °C and analyzed the microstructure to establish its correlation with TE properties. The TE transport properties were measured between room temperature and 800 °C, and electronic properties were calculated from first principles calculations. Herein, we introduced second and third phases into a ZnO-based matrix to enhance its power factor (PF) by charge carrier energy filtering by applying co-doping with Al and Ti. Although multiphase materials usually do not exhibit high PF, in this study, it is observed that three-phase ZnO-based materials exhibit higher PF values compared to the two-phase materials. We observed unusual behavior, in which the Seebeck coefficient ( ) and electrical conductivity (σ) values increased simultaneously with temperature for ZnAlTiO, originating from energy filtering of charge carriers due to both co-doping and the peculiar multiphase structure. High σ values were associated with the increase of electron concentration, while high values were due to Fermi energy tuning and heavier effective masses initiated by Al and Ti co-doping. Besides increasing the PF, the multiphase structure played an essential role in reducing lattice thermal conductivity due to phonon scattering by the Umklapp, point defect, and second-phase mechanisms. Our approach yielded an increase of the TE figure of merit upon formation of a three-phase 2 wt % Ti-doped ZnAlO compound of ca. 10 times compared to the corresponding value attained for its two-phase ZnAlO counterpart.
氧化锌是一种适用于高温应用的很有前景的热电材料；然而，其热电性能受到电输运和热输运之间强耦合的限制。在本研究中，我们通过固态反应和在1500℃下的空气烧结合成了铝和钛共掺杂的氧化锌，并分析了微观结构以建立其与热电性能的相关性。在室温至800℃之间测量了热电输运性能，并根据第一性原理计算得出电子性能。在此，我们通过铝和钛的共掺杂，将第二相和第三相引入氧化锌基基体中，通过电荷载流子能量过滤来提高其功率因子（PF）。尽管多相材料通常不会表现出高PF，但在本研究中观察到，三相氧化锌基材料比两相材料表现出更高的PF值。我们观察到一种不寻常的行为，即对于ZnAlTiO，塞贝克系数（ ）和电导率（σ）值随温度同时增加，这源于共掺杂和特殊的多相结构导致的电荷载流子能量过滤。高σ值与电子浓度的增加有关，而高 值则归因于铝和钛共掺杂引发的费米能调谐和更重的有效质量。除了提高PF外，多相结构在降低晶格热导率方面也起着至关重要的作用，这是由于Umklapp、点缺陷和第二相机制引起的声子散射。我们的方法在形成2 wt%钛掺杂的三相ZnAlO化合物时，使热电优值提高了约10倍，相比其两相ZnAlO对应物所达到的相应值。
