Ultra-low lattice thermal conductivity driven high thermoelectric figure of merit in Sb/W co-doped GeTe

High thermoelectric performance is a material challenge associated mainly with the manipulation of lattice dynamics to obtain extrinsic phonon transport routes, which can make the lattice thermal conductivity ( κ lat ) intrinsically low by introducing multiple scattering mechanisms. The present study shows that the lattice-strain-induced phonon scattering resulting from microstructural distortions in GeTe-based compounds can enable ultralow lattice thermal conductivity. The unusual lattice shrinkage, W interstitials, W nanoprecipitates, and heavy elemental mass, in Ge 0.85 Sb 0.1 W 0.05 Te culminate in an ultralow lattice thermal conductivity of ∼0.2 W m −1 K −1 at 825 K. Microstructural distortions in this Sb/W co-doped GeTe are found to be primarily associated with shorter W–Te bonding owing to the anomalous effect of the higher electronegativity of the W atoms. Furthermore, the increased electrical conductivity ( σ ) resulting from the enhanced vacancy formation caused by W doping and W interstitials synergistically contributes to optimization of the thermoelectric performance ( ZT ) to ∼2.93 at 825 K. The thermoelectric efficiency ( η ) as high as ∼17% has been obtained for a single leg in this composition at an operating temperature of 825 K, with an estimated device ZT value of ∼1.38.