P-type PbTe is one of the most representative high-performance thermoelectric materials, while the conversion efficiency of the fabricated module is limited by the relatively low zT of n-type PbTe. Here, we report the optimization of Cu-doped n-type PbTe by tuning the ionic migration energy, aiming for the high-efficiency and robust modules. It is revealed that the strategy of lattice contraction, achieved by Ge/Se co-doping, preserves the excellent carrier mobility from interstitial Cu and suppresses the unstable transport at high temperature. In the optimized sample of Pb_0.94Ge_0.06Cu_0.02Se_0.04Te_0.96, a superior average zT (300–823 K) of 1.04 and a high peak zT of 1.45 at 823 K are obtained. A remarkable conversion efficiency of 10.5% at a temperature difference of 500 K is achieved in the fabricated PbTe-based module.

Cobalt oxide, as one of the most fascinating examples of correlated electronic system, exhibits several exotic transport characteristics, such as superconductivity, charge ordering, and topological frustration. In this study, we are reporting the observation of another intriguing transport phenomenon in calcium cobaltates. Specifically, under a large magnetic field of 7 T, we observed an anomalously enhanced thermal conductivity that was accompanied with a largely suppressed thermopower. This observation reveals a hitherto undiscovered correlation between the two transport factors. Within the premise of Heisenberg model, we have shown that the observed experimental results can be explained consistently only if the magnon excitation is taken into account. Our study offers an insight into the puzzling origin of large thermopower observed in layered cobaltates and provides a specific strategy for further optimization of thermopower.