High figure-of-merit and power generation in high-entropy GeTe-based thermoelectrics

Abstract

The high-entropy concept provides extended, optimized space of a composition, resulting in unusual transport phenomena and excellent thermoelectric performance. By tuning electron and phonon localization, we enhanced the figure-of-merit value to 2.7 at 750 kelvin in germanium telluride–based high-entropy materials and realized a high experimental conversion efficiency of 13.3% at a temperature difference of 506 kelvin with the fabricated segmented module. By increasing the entropy, the increased crystal symmetry delocalized the distribution of electrons in the distorted rhombohedral structure, resulting in band convergence and improved electrical properties. By contrast, the localized phonons from the entropy-induced disorder dampened the propagation of transverse phonons, which was the origin of the increased anharmonicity and largely depressed lattice thermal conductivity. We provide a paradigm for tuning electron and phonon localization by entropy manipulation, but we have also demonstrated a route for improving the performance of high-entropy thermoelectric materials.

Tunable quantum gaps to decouple carrier and phonon transport leading to high-performance thermoelectrics

“…Our study here further improves the peak ZT to 2.6 at 673 K and ZT average to 1.6 (323–723 K). Although the recent work reports a higher peak ZT (2.7) and ZT average (1.7) via the strategy of high entropy in GeTe systems 40 , it contains 12% toxic Pb in the cation position, which makes it not comparable with this work in terms of environmentally friendly power-generation applications. Thus the reported thermoelectric performance in this work is competitive for lead-free GeTe-based polycrystal thermoelectrics.…”

Enhanced Thermoelectric Performance of GeTe-Based Composites Incorporated with Fe Nanoparticles

“…And the electronic thermal conductivity ( κ e ), part of the total thermal conductivity ( κ total ), has a positive correlation with σ. Since these coefficients of TE materials are strongly correlated, the optimized methods such as nanostructuring, − solid solution alloying, , band engineering, , and high-entropy alloying are appropriately used to increase the electronic properties and reduce the lattice thermal conductivity ( κ L ) simultaneously and finally improve the thermoelectric properties.…”

“…The κ L of lead-free GeTe TE material (0.85 W m –1 K –1 at 685 K) is not the lowest; however, it undergoes a structural phase transition from rhombohedral GeTe (r-GeTe) to cubic GeTe (c-GeTe) around 690 K and presents a multiband structure, which can be modulated with much freedom for the optimization of performance. − GeTe-based TE materials have the potential to develop into an alternative material to PbTe in the mid-temperature region . The latest research suggests that the ZT was enhanced to 2.7 at 750 K in the high-entropy Ge 0.61 Ag 0.11 Sb 0.13 Pb 0.12 Bi 0.01 Te, benefitting from the increased crystal symmetry and anharmonicity . Single-phase alloys have been well studied with five times the number of publications on multiphase/composite TE materials, but investigating composites is one of the most viable strategies to enhance thermoelectric performance by designing new materials .…”

Synergistic Effect of Work Function and Acoustic Impedance Mismatch for Improved Thermoelectric Performance in GeTe-WC Composite

“…However, pristine GeTe suffers from the intrinsic Ge vacancies that result in a high hole carrier concentration (∼10 21 cm –3 ), high thermal conductivity (∼8 W·m –1 ·K –1 ), and low Seebeck coefficient (∼30 μV·K –1 ) and hence poor zT . Several innovative approaches have been demonstrated in recent times to achieve enhanced thermoelectric performance in GeTe including manipulation of Ge vacancies, band convergence, − crystal structure modification, , resonance-level doping , high-entropy concept, and so forth and are based on the atomic doping strategies. Herein, we demonstrate a novel composite approach that considers the optimized GeTe (Ge 0.87 Mn 0.05 Sb 0.08 Te via band-structure and lattice dynamics engineering) as matrix and tungsten carbide (WC: possesses higher electrical and thermal conductivity than Ge 0.87 Mn 0.05 Sb 0.08 Te) as the second phase.…”