Contrasting the Roles of Cu Interstitials and Sb Substitutions in Regulating Ferroelectric Distortions and Thermoelectric Properties of α-GeTe

α-GeTe has attracted intensive attention recently due to its intriguing ferroelectric distortion as a freedom to engineer thermoelectric properties. However, pristine α-GeTe features overhigh carrier concentration (∼10 21 cm –3 ) that degrades the overall performance. In this study, Sb substitutions and Cu interstitials are employed to neutralize the excess holes in α-GeTe. It is revealed that, while both Sb and Cu dopants serve as effective electron donors, they have notably different influences on the structural parameters of α-GeTe. Cu interstitials exert negligible impact on the ferroelectric distortion of α-GeTe. By contrast, Sb substitutions for Ge tend to improve the structure symmetry and valence band degeneracy. As a consequence, Ge 1– x Sb x Te shows a much enhanced Seebeck coefficient. Meanwhile, Ge 1– x Sb x Te displays lower lattice thermal conductivities than Cu y GeTe, particularly around ambient temperatures, because of the pronounced ferroelectric instability. Ge 0.92 Sb 0.08 Te shows a highest ZT value of ∼1.5 at 723 K, which is ∼60% higher than that of the pristine α-GeTe.