Halpin John E, Jenkins Benjamin, Moody Michael P, Webster Robert W H, Bos Jan-Willem G, Bagot Paul A J, MacLaren Donald A
SUPA, School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, U.K.
Department of Materials, University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, U.K.
ACS Appl Electron Mater. 2022 Sep 27;4(9):4446-4454. doi: 10.1021/acsaelm.2c00699. Epub 2022 Aug 23.
The performance of thermoelectric materials depends on both their atomic-scale chemistry and the nature of microstructural details such as grain boundaries and inclusions. Here, the elemental distribution throughout a TiNiCuSn thermoelectric material has been examined in a correlative study deploying atom-probe tomography (APT) and electron microscopies and spectroscopies. Elemental mapping and electron diffraction reveal two distinct types of grain boundary that are either topologically rough and meandering in profile or more regular and geometric. Transmission electron microscopy studies indicate that the Cu dopant segregates at both grain boundary types, attributed to extrusion from the bulk during hot-pressing. The geometric boundaries are found to have a degree of crystallographic coherence between neighboring grains; the rough boundaries are decorated with oxide impurity precipitates. APT was used to study the three-dimensional character of rough grain boundaries and reveals that Cu is present as discrete, elongated nanoprecipitates cosegregating alongside larger substoichiometric titanium oxide precipitates. Away from the grain boundary, the alloy microstructure is relatively homogeneous, and the atom-probe results suggest a statistical and uniform distribution of Cu with no evidence for segregation within grains. The extrusion suggests a solubility limit for Cu in the bulk material, with the potential to influence carrier and phonon transport properties across grain boundaries. These results underline the importance of fully understanding localized variations in chemistry that influence the functionality of materials, particularly at grain boundaries.
热电材料的性能取决于其原子尺度的化学性质以及诸如晶界和夹杂物等微观结构细节的性质。在此，通过结合原子探针断层扫描（APT）以及电子显微镜和光谱学的相关研究，对整个TiNiCuSn热电材料中的元素分布进行了研究。元素映射和电子衍射揭示了两种不同类型的晶界，一种在轮廓上拓扑粗糙且蜿蜒曲折，另一种则更为规则且呈几何形状。透射电子显微镜研究表明，Cu掺杂剂在两种晶界类型处均发生偏析，这归因于热压过程中从块体中挤出。发现几何晶界在相邻晶粒之间具有一定程度的晶体学连贯性；粗糙晶界上装饰有氧化物杂质沉淀。APT用于研究粗糙晶界的三维特征，结果表明Cu以离散的、细长的纳米沉淀形式存在，与较大的亚化学计量钛氧化物沉淀共偏析。远离晶界处，合金微观结构相对均匀，原子探针结果表明Cu呈统计均匀分布，没有证据表明其在晶粒内偏析。这种挤出表明Cu在块体材料中的溶解度极限，这有可能影响跨晶界的载流子和声子传输特性。这些结果强调了全面理解影响材料功能的化学局部变化的重要性，尤其是在晶界处。
