Recently, researchers led by Prof. ZHANG Yongsheng from the Institute of Solid State Physics of the Hefei Institutes of Physical Science (HFIPS), made important progress in the research of defect behaviors at the interface of XTe (X=Ca, Sr, Ba) nanostructured PbTe.

"Our work not only elucidates the lowest energy defects in Lead telluride (PbTe)-based materials, but also paves the way to understanding and designing promising thermoelectrics with interface phases," said Prof. ZHANG Yongsheng, lead author of the study.

According to him, the solid solution PbTe/SrTe interface environment could further decrease the formation energies of the low-energy defect (Na^1-_Pb/Sr), which plays an important role in increasing the Na concentration in the Lead telluride (PbTe) based thermoelectric compounds.

PbTe is a traditional thermoelectric material with high performance in the mid temperature range (500–800 K). In recent years, researchers have been working to further optimize its thermoelectric properties by band and defect engineering. However, the physical mechanism of defects in the precipitated phase interface is still unclear, which hinders the realization of further regulating thermoelectric properties of PbTe based compounds by precipitating and doping.

To solve the problems, this team scrutinized the experimental observations of SrTe precipitated in PbTe with Na doping and discovered that the PbTe/SrTe interface was a wide PbSrTe solid solution region rather than a clear coherent/semicoherent interface. Correspondingly, they designed a PbTe/PbXTe/XTe pseudo-interface model and systematically investigated the intrinsic and extrinsic (Na) defect behaviors in the three parts included at different chemical potential environments.

To understand the defect stability, they also aligned the Fermi levels of the three parts, and obtained the comparable defect formation energies in this system.

The research was supported by the National Natural Science Foundation of China, NSF DMREF and United States Department of Energy through the Computational Science Graduate Fellowship. The calculations were performed in the Computational Science of HFIPS, the ScGrid of Supercomputing Center, and the Computer Network Information Center of the Chinese Academy of Science.

Fig. 1. Schematic of the concentration distribution of Na doping in PbTe-XTe, and its effect on thermoelectric properties (Seebeck coefficient, conductivity, thermal conductivity). (Image by ZHANG Xuemei)

Fig. 2. Schematic of the PbTe/PbXTe/XTe pseudo-interface, including three parts: (a) The bulk PbTe, (b) the solid solution of Pb0.5X0.5Te (X= Ca, Sr, Ba), and (c) XTe. (Image by ZHANG Xuemei)