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HL: Fachverband Halbleiterphysik

HL 33: 2D Materials and Heterostructures: Optoelectronics

HL 33.4: Talk

Wednesday, March 20, 2024, 15:45–16:00, EW 201

High-entropy thermoelectrics: what is the role of metavalent bonding? — •Nan Lin¹, Dongwang Yang², Yuan Yu¹, and Matthias Wuttig¹ — ¹Institute of Physics (IA), RWTH Aachen University, 52056 Aachen, Germany — ²State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China

The design principle of high-entropy (HE) thermoelectrics is still elusive because forming a solid solution is the prerequisite to enhance the configurational entropy. Typical HE thermoelectrics have been mainly realized in chalcogenides such as PbTe and GeTe, etc. Interestingly, these chalcogenides also show an unconventional chemical bonding mechanism, termed metavalent bonding (MVB). Is there a strong coincidence of correlation between HE thermoelectrics and MVB? To answer this question, we designed PbQ-AgBiQ2 (Q = S, Se, Te) samples to study their microstructures and bonding mechanisms, as well as thermoelectric properties. We observe no obvious phase separations in these alloys. Atom probe tomography measurements also confirm the abnormal bond-breaking behavior, corroborating their bonding mechanism. Moreover, the maximum optical absorption decreases from Q = Te to Q = Se and then to Q=S due to the increased charge transfer. This also leads to the weakening of MVB. The thermoelectric properties decrease with increasing the charge transfer numbers from tellurides to sulfides. This work indicates that mixing metavalently bonded solids with a controlled degree of charge transfer could be an important avenue for designing HE thermoelectrics.

Keywords: High-entropy alloys; Thermoelectric materials; Metavalent bonding; Charge transfer