Tsai, Yi FenYi FenTsaiChao, Ying ChunYing ChunChaoHsing, Cheng RongCheng RongHsingWang, Kuang KuoKuang KuoWangTung, Yung HsiangYung HsiangTungYang, Chun ChuenChun ChuenYangChen, Sinn WenSinn WenChenSnyder, G. JeffreyG. JeffreySnyderHUNG-WEI YENWei, Ching MingChing MingWeiWei, Pai ChunPai ChunWeiHSIN-JAY WU2024-01-292024-01-292024-02-1513596454https://scholars.lib.ntu.edu.tw/handle/123456789/639157This study investigates the structure, microstructure, and transport properties of off-stoichiometric GeTe (off-GeTe). In a narrow range of 50–53 at% Te, both the rhombohedral a-GeTe and orthorhombic g-GeTe phases coexist. Despite their similar chemical composition, GeTe and off-GeTe alloys exhibit distinct microstructural and thermal/electronic properties. Theoretical density functional theory (DFT) calculations were employed to verify that changes in the Ge/Te ratios influence the concentration of Ge vacancies, leading to a significant alteration in transport properties despite minor variations in chemical compositions. The off-GeTe alloy, which is free of Ge precipitates, displays defective domain boundaries, showcasing a non-typical herringbone nanostructure that is unprecedented for GeTe-based materials. Notably, the phase transition temperature of off-GeTe, at 620K, differs from its peak zT temperature of 698K. Moreover, a TE device incorporating off-GeTe demonstrates superior interfacial stability and higher energy conversion efficiency compared to its stoichiometric GeTe counterpart. Consequently, off-GeTe demonstrates superior TE performance and enhanced interfacial stability compared to stoichiometric GeTe. The addition of Sb to off-GeTe further improves its potential for TE applications by lifting the single-leg conversion efficiency greater than 3%.Defective domain boundaries | Off-stoichiometric GeTe | Theoretical density functional theory (DFT) | Thermoelectric[SDGs]SDG7journal article10.1016/j.actamat.2023.1196442-s2.0-85181777258https://api.elsevier.com/content/abstract/scopus_id/85181777258