Leverage between Spinodal Fluctuations and Athermal Transformation in Dilute PbTe Alloying GeTe Thermoelectrics

Tellurium-based chalcogenides have taken the lead at mid-temperature thermoelectric (TE) generators since the 1960s. Most electron- or hole-doped chalcogenides outshine the other TE alloys above 700 K as they stabilize in a cubic structure. Although the rocksalt-type TE alloys with high-dose dopants show promising TE performance, their structural stability could be a concern when exposed to a large thermal gradient atmosphere. This issue has become more severe for GeTe-based phase-change alloys whose volumetric mismatch and discontinuous transport properties could be magnified upon heavily doping. Hence, dilute impurity doping provides a rational pathway for designing thermally robust and high-performance GeTe-based alloys. In this regard, phase diagram engineering probes the leverage between the diffusion-driven spinodal decomposition and diffusion-less athermal transformation, which fulfills the microstructure evolution and enables the decoupling between the reduced lattice thermal conductivity κL and enhanced power factor PF= S2 ρ -1. In this work, a synergy between dilute impurity doping and microstructural engineering yields an ultralow lattice thermal conductivity κL < 0.5 Wm-1K-1 and a peak zT of 1.1. at 648 K in a light-doped Pb0.05Ge0.95Te.