The role of surface oxygen chemisorption on impurity states and electron localization in n-type PbTe: Ar-protected grinding as a remedy for tripling ZT

Abstract

Optimizing the thermoelectric performance of n-type PbTe is crucial for developing practical PbTe-based devices. Ubiquitous air exposure during processing severely degrades its carrier concentration and electrical properties, yet the underlying mechanism remains unclear. Combining first-principles calculations with cryogenic transport measurements, we reveal that mechanical processing triggers oxygen chemisorption on fresh PbTe surfaces, forming detrimental X_Pb + O_Te + V_Pb (X = Bi/Sb) defect complexes that fundamentally modify the electronic structure. Pronounced charge localization at dopant sites and adjacent Te atoms suppresses the orbital hybridization between the dopant atoms and PbTe, shifting the impurity level toward the valence band. This detrimental electronic renormalization markedly reduces the carrier concentration and carrier mobility. For Sb-doped PbTe under oxidation, strong Sb–O bonds “lock” valence electrons, disrupting the original Sb–Te hybridization and resulting in degraded carrier mobility. In contrast, the weaker tendency of Bi to hybridize with O preserves its favorable electronic structure upon air exposure. By eliminating oxygen adsorption through inert atmosphere processing, we significantly enhance the hybridization of Sb-5p/Bi-6p with Pb-6p and Te-5p, shifting the energy levels toward the conduction band minimum. Consequently, oxidation-free Pb_0.995Sb_0.005Te-Ar achieves a ZT_max of ∼1.3 and ZT_ave of ∼0.84, doubling the performance of air-exposed samples (ZT_max ∼ 0.45; ZT_ave ∼ 0.24).