Realizing high average zT in GeTe through band modulation and suppressing Ge vacancies

Abstract

<p>GeTe is regarded as an excellent thermoelectric material, while its intrinsically high hole concentration impedes its further enhancement in thermoelectric performance. In this work, we introduce a two-step strategy by Bi and Y co-doping and Pb alloying to optimize the thermoelectric properties of the GeTe compound. Aliovalent Bi doping on the Ge site is found to effectively reduce the hole concentration, and a small substitution of Bi by Y atoms can further increase the effective mass, resulting in a high thermoelectric figure of merit (<em>zT</em>) of ∼ 1.92 at 723 K. Alloying Pb with high concentration elaborately decreases the carrier concentration to around 1.09 × 10²⁰ cm⁻³, leading to an enhancement of Seebeck coefficient. In addition, Pb alloying maintains stable carrier mobility, contributing to a high power factor. PbTe alloying induces a strong point defect scattering and strain field fluctuation, leading to a low lattice <a href="https://www.sciencedirect.com/topics/physics-and-astronomy/thermal-conductivity" title="Learn more about thermal conductivity from ScienceDirect's AI-generated Topic Pages">thermal conductivity</a>. Benefiting from the synergistically optimized effects of Bi and Y co-doping and Pb alloying, a peak <em>zT</em> of ∼ 2.26 at 723 K and an average <em>zT</em> of 1.64 over 300–773 K are realized in Ge_0.8Pb_0.15Bi_0.04Y_0.01Te.<br></p>