Recently, the research team from Shanghai Jiao Tong University, cooperated with the scientists from Shanghai Institute of Ceramics and Shanghai Institute of Micro-System and Information Technology, made new progress in the atomic structure regulation and performance optimization of Zintl phase high-entropy thermoelectric materials. Relevant results have been published in the journal of Science Advances entitled “Atomic to nanoscale chemical fluctuations: The catalyst for enhanced thermoelectric performance in high-entropy materials” (DOI:10.1126/sciadv.adt6298).
High-entropy materials have expanded the frontier for discovering uncharted physicochemical properties. In high-entropy thermoelectric (TE) materials, differences in electronegativity, atomic mass, and atomic radius among multiple solid-solution elements give rise to phenomena such as chemical fluctuation, chemical ordering, and potential phase separation. These phenomena introduce new degrees of freedom for tuning TE performance. However, traditional microstructural studies have mainly concentrated on dislocations, nanoprecipitates, and grain boundaries, but the intricate role of chemical fluctuations is often overlooked. Additionally, the multiscale nature of chemical fluctuations, spanning from atomic to microscale, complicates the further analysis.
In this work, the authors synthesized a series of high-entropy (Mg0.94-nYb0.26Sr0.26Znm)(MgnCd0.69Zn0.69-mNax)(Sb1.74Ca0.26) single-phase materials with homogeneous elemental distribution at the microscopic scale. Employing a suite of advanced characterization techniques, they unveiled the precise atomic occupancy of various elements within the high-entropy structure, notably the anomalous positioning of cationic Ca at the anionic Sb site. They discovered atomic to nanoscale chemical fluctuations that, despite the compositional disparities, maintain a coherent atomic lattice. These fluctuations, along with the unusual atomic occupations, lead to an exceptionally low lattice thermal conductivity akin to that of amorphous materials. Combining the optimized carrier concentration and well-maintained carrier mobility, the authors ultimately achieved a high zT value of 1.2 at 750 K, outperforming most previously reported AB2Sb2-type Zintls. This study underscores that the atomic to nanoscale chemical fluctuations are the crucial catalyst for the enhanced thermoelectric performance in high-entropy materials.
This work was supported by the National Outstanding Youth Program, National Natural Science Foundation of China, and Shanghai Pilot Program for Basic Research-Chinese Academy of Science, Shanghai Branch.
The paper link is as follows:
https://www.science.org/doi/10.1126/sciadv.adt6298
Fig. 1. High-performance Zintl phase TE materials with chemical fluctuations. (A) Schematic diagram of atomic to nanoscale chemical fluctuations in high-entropy materials. (B) Room temperature lattice thermal conductivity κL as a function of configuration entropy ΔS for our high-entropy sample (Mg0.94-nYb0.26Sr0.26Znm)(MgnCd0.69Zn0.69-mNax)(Sb1.74Ca0.26). The dashed red line denotes the theoretical lattice thermal conductivity calculated through the Callaway Model. (C) Figure of merit zT at 750 K as a function of configuration entropy ΔS. The reported data of p-type Mg3Sb2-based multicomponent samples are included for comparison.
Fig. 2. Chemical fluctuations at the nanoscale of high-entropy materials. (A) Three-dimensional reconstruction mappings obtained from the APT technique for the [(Mg0.25Yb0.25Ca0.25Sr0.25)(Mg0.33Zn0.33Cd0.33)2]1.17Na0.013Sb2 sample, illustrating the variations in concentrations of the Mg, Yb, Sr, Ca, Cd, Zn, Na and Sb elements. (B) High-angle annular dark field (HAADF) image and corresponding EDS mapping. (C) Relative content of different elements of the dark region I, grey region II, and white region III marked in (B). The red dashed line denotes the relative average content of each element. (D) Enlarged HAADF image. (E) Fast Fourier transformed (FFT) images of the three different regions in (B).
Fig. 3. Chemical fluctuations at the atomic scale in high-entropy materials. (A) Atomic-resolution HAADF-STEM images of high-entropy (Mg0.94-nYb0.26Sr0.26Znm)(MgnCd0.69Zn0.69-mNa0.013)(Sb1.74Ca0.26) sample. (B) Corresponding atomic structure model of Zintl phase AB2Sb2. (C) Atomic-resolution STEM-EDS mappings of various elements. Atomic structure model of AB2Sb2 is added in the upper right corner of each figure to calibrate the atomic occupations.
Fig. 4. Electrical and thermal properties of high-entropy materials. (A) Low-temperature lattice thermal conductivity κL as a function of temperature for (Mg0.94-nYb0.26Sr0.26Znm)(MgnCd0.69Zn0.69-m)(Sb1.74Ca0.26) sample. The data of Mg3.2Sb1.195Bi0.795Te0.01, single-crystal Mg3Sb2, crystalline SiO2, and amorphous SiO2 are included for comparison. (B) Contributions from various phonon scattering mechanisms to the lattice thermal conductivity κL. U, B, P, and NP denote the phonon–phonon Umklapp process, grain boundary scattering, point defect scattering, and nanoparticles scattering, respectively. (C) Carrier mobility μ and (D) carrier concentration p as functions of Na content x for (Mg0.94-nYb0.26Sr0.26Znm)(MgnCd0.69Zn0.69-mNax)(Sb1.74Ca0.26), where x = 0, 0.006, 0.01, 0.013, 0.015, and 0.02. Reported data of Mg3-xNaxSb2 are included for comparison.
Author: Haotian Gao