Local Chemical Fluctuation and Lattice Thermal Conductivity of High-Entropy Thermoelectric Materials

High-entropy materials, which consist of multiple elements occupying the same crystallographic site, have emerged as the promising materials for a variety of applications [1,2]. With the mutual interaction of different elements, local chemical fluctuation arises in high-entropy structures and largely enhances the properties of various materials included metallic alloys [3], Li-ion batteries [4], and catalysts [5]. Recently, this high-entropy strategy has also been applied to enhance the performance of thermoelectric materials with the combination of multiple elements [6,7]. The local chemical fluctuation could dampen the propagation of heat-carrying phonons and thus largely reduce lattice thermal conductivity of thermoelectric materials.<br/> <br/>However, these studies of high-entropy materials have lacked the attention on the role of each constituent elements on local chemical fluctuation, which is crucial for tailoring the local chemical fluctuation by selecting specific element. Herein, we have identified the respective contributions of the element characteristics (atomic mass, radius, and electronegativity) on the local chemical fluctuation by determining atomic-scale distributions and concentrations of various elements in GeTe, SnTe and PbTe-based high-entropy thermoelectric materials. The electronegativity is found to have a comparable influence with the mass on the elemental fluctuations while the slight contribution is from the radius. The local chemical fluctuation is further tailored by selecting specific elements to induce large lattice distortion and strong strain fluctuation in the GeTe-based high-entropy materials for lowering lattice thermal conductivity independent of the increased entropy by adding more elements. With the comparison of GeTe-AgSbX (X=Sn, Mn and Pb) high-entropy materials, we have also identified the noticeable contribution of electronegativity difference to the lattice thermal conductivity in addition to the known effect of mass and size differences. Our findings of local chemical fluctuation and lattice thermal conductivity provide the basis for tuning the structure and property of high-entropy materials by selecting specific elements.<br/> <br/><b>References</b><br/>1. George E P, Raabe D, Ritchie R O. High-entropy alloys. Nature Reviews Materials, 2019, 4(8): 515-534.<br/>2. Dragoe N, Bérardan D. Order emerging from disorder. Science, 2019, 366(6465): 573-574.<br/>3. Ding Q, Zhang Y, Chen X, et al. Tuning element distribution, structure and properties by composition in high-entropy alloys. Nature, 2019, 574(7777): 223-227.<br/>4. Sarkar A, Velasco L, Wang D, et al. High entropy oxides for reversible energy storage. Nature Communications, 2018, 9(1): 3400.<br/>5. Yao Y, Huang Z, Xie P, et al. Carbothermal shock synthesis of high-entropy-alloy nanoparticles. Science, 2018, 359(6383): 1489-1494.<br/>6. Jiang B, Yu Y, Cui J, et al. High-entropy-stabilized chalcogenides with high thermoelectric performance. Science, 2021, 371(6531): 830-834.<br/>7. Jiang B, Wang W, Liu S, et al. High figure-of-merit and power generation in high-entropy GeTe-based thermoelectrics. Science, 2022, 377(6602): 208-213.