Realizing zT of 2.3 in Ge_1−x−ySb_xIn_yTe via Reducing the Phase‐Transition Temperature and Introducing Resonant Energy Doping

Abstract

GeTe with rhombohedral-to-cubic phase transition is a promising lead-free thermoelectric candidate. Herein, theoretical studies reveal that cubic GeTe has superior thermoelectric behavior, which is linked to (1) the two valence bands to enhance the electronic transport coefficients and (2) stronger enharmonic phonon-phonon interactions to ensure a lower intrinsic thermal conductivity. Experimentally, based on Ge Sb Te with optimized carrier concentration, a record-high figure-of-merit of 2.3 is achieved via further doping with In, which induces the distortion of the density of states near the Fermi level. Moreover, Sb and In codoping reduces the phase-transition temperature to extend the better thermoelectric behavior of cubic GeTe to low temperature. Additionally, electronic microscopy characterization demonstrates grain boundaries, a high-density of stacking faults, and nanoscale precipitates, which together with the inevitable point defects result in a dramatically decreased thermal conductivity. The fundamental investigation and experimental demonstration provide an important direction for the development of high-performance Pb-free thermoelectric materials.

Promising and Eco‐Friendly Cu2X‐Based Thermoelectric Materials: Progress and Applications

“…Hong et al reported a peak zT value higher than 2 at ≈580 K. From ≈650 to ≈800 K, the peak zT values of GeTe‐based thermoelectric materials are higher than 1 . Further studies have enhanced the peak zT values of GeTe‐based thermoelectric materials to a level higher than 2 . Under this temperature range (from ≈650 to ≈800 K), other p‐type thermoelectric materials, such as SnSe and higher manganese silicide have also drawn extensive research interests due to either low cost or high performance.…”

Manipulating the Ge Vacancies and Ge Precipitates through Cr Doping for Realizing the High‐Performance GeTe Thermoelectric Material

“…[ 38 ] Therefore, many previous studies for improving thermoelectric GeTe focus on optimizing the carrier concentration. [ 39–45 ] An obvious solution is doping of elements acting as electron donors to decrease the hole carrier concentration. For example, Bi and Sb have been reported to be effective donors to decrease the carrier concentration.…”

Anharmonic stabilization and lattice heat transport in rocksalt β-GeTe

“…A very high zT of 2.3 has been reported in Sb and In co-doped β-GeTe owning to the superior electronic properties and low κ l . 13 It is suggested that the phase transition from the lowsymmetry rhombohedral α-GeTe to the high-symmetry rocksalt β-GeTe plays a crucial role in enhancing thermoelectric efficiency through converging band pockets and suppressing κ l . 2,12,13 Therefore, it is fundamentally important to understand the lattice dynamics and thermal transport in β-GeTe, insight into which may enable further reduction of κ l and enhancement of zT .…”

“…Motived by this point, we perform firsta) Electronic mail: yxia@anl.gov b) Electronic mail: mchan@anl.gov arXiv:1807.08012v2 [cond-mat.mtrl-sci] 6 Sep 2018 principles-based calculations of lattice dynamics and thermal transport properties of β-GeTe at 800 K, near the temperature of optimal experimental thermoelectric performance. 13 To resolve the imaginary phonon modes, we present an effective scheme to account for temperature effect by explicitly including anharmonicity up to 4th order, with a particular focus on temperature-induced anharmonic phonon renormalization (PRN) and four-phonon scattering. Phonon dispersions and atom-projected densities of states for rocksalt β-GeTe computed at 0 K (a) and 800 K (b), respectively.…”