Eutectoid nano-precipitates inducing remarkably enhanced thermoelectric performance in (Sn1-xCdxTe)1-y(Cu2Te)y

Due to its similar crystallographic and electronic band structure to PbTe, SnTe becomes a natural alternative to PbTe for promising mid-temperature thermoelectric power generation and refrigeration. The bottleneck which restricts the thermoelectric performance of SnTe lies mainly in its relatively high lattice thermal conductivity. In this work, we found that co-doping SnTe with Cd and CuTe leads to "eutectoid" precipitation of CdTe- and CuTe-based nano-phases, which (together with Cu interstitials) can reduce the lattice thermal conductivity from ∼1.0 W m K for pristine SnTe to a remarkably lower level of ∼0.42 W m K for (SnCdTe)(CuTe) at 823 K. With further valence band convergence by Cd substitution and carrier concentration optimization by I-doping, we obtained a significantly enhanced figure of merit ZT of ∼1.42 at 823 K in (SnCdTe)(CuTe)-1%I. Interestingly, temperature dependent XRD measurements excluded the dynamic solution of CdTe or CuTe in the SnTe matrix and consequent phonon scattering reinforcement as reported. Overall, our finding of "eutectoid" precipitation of high-density CdTe/CuTe nano-phases, as strong scatters for mid-frequency heat-carrying phonons, might shed light on future studies on reducing lattice thermal conductivity in SnTe and related thermoelectric material systems.