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

Abstract

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 Cu₂Te leads to “eutectoid” precipitation of CdTe- and Cu₂Te-based nano-phases, which (together with Cu interstitials) can reduce the lattice thermal conductivity from ∼1.0 W m⁻¹ K⁻¹ for pristine SnTe to a remarkably lower level of ∼0.42 W m⁻¹ K⁻¹ for (Sn_0.95Cd_0.05Te)_0.95(Cu₂Te)_0.05 at 823 K. With further valence band convergence by Cd_Sn substitution and carrier concentration optimization by I-doping, we obtained a significantly enhanced figure of merit ZT of ∼1.42 at 823 K in (Sn_0.95Cd_0.05Te)_0.93(Cu₂Te)_0.07-1%I. Interestingly, temperature dependent XRD measurements excluded the dynamic solution of CdTe or Cu₂Te in the SnTe matrix and consequent phonon scattering reinforcement as reported. Overall, our finding of “eutectoid” precipitation of high-density CdTe/Cu₂Te 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.