Atomic Local Ordering and Alloying Effects on the Mg₃(Sb_1-x Bi _x )₂ Thermoelectric Material

P Ouyang and MH Yuan and PB Tang and Q Zhang and SH Liu and J Shuai and XG Li, ACS APPLIED MATERIALS & INTERFACES, 15, 37554-37562 (2023).

DOI: 10.1021/acsami.3c07801

Mg-3(Sb1-x Bi x )(2) alloy has been extensivelystudiedin the last 5 years due to its exceptional thermoelectric (TE) performance.The absence of accurate force field for inorganic alloy compoundspresents great challenges for computational studies. Here, we explorethe atomic microstructure, thermal, and elastic properties of theMg(3)(Sb1-x Bi x )(2) alloy at different solution concentrationsthrough atomic simulations with a highly accurate machine learninginteratomic potential (ML-IAP). We find atomic local ordering in theoptimized structure with the Bi-Bi pair inclined to join adjacentlayers and Sb-Sb pair preferring to stay within the same layer.The thermal conductivity changes with the solution concentrationscan be correctly predicted through ML-IAP-based molecular dynamicssimulations. Spectral thermal conductance analysis shows that thecontinuous movement of low-frequency peak to high frequency is responsiblefor the reduction of the thermal conductivity upon alloying. Elasticcalculations reveal that similar to the thermal conductivity, solidsolution alloying can reduce the overall elastic properties at bothMg(3)Sb(2) and Mg3Bi2 ends,while anisotropic behavior is clearly observed with linear interpolationrelationship upon alloying along the interlayer direction and nonlinearityalong the intralayer direction. Although the atomic local orderingshows little effects on the properties of the Mg-3(Sb1-x Bi x )(2) alloy with only two alloying elements, it possesses potentialimportant impacts on multiprincipal element inorganic TE alloys. Thiswork provides a recipe for computational studies on the TE alloy systemsand thus can accelerate the discovery and optimization of TE materialswith high TE performance.

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