Enhanced thermoelectric performance and mechanical strength in GeTe enable power generation and cooling

Finding a real thermoelectric(TE)material that excels in various aspects of TE performance,mechanical properties,TE power generation,and cooling is challenging for its commercialization.Herein,we report a novel multifunctional Ge0.78Cd0.06Pb0.1Sb0.06Te material with excellent TE performance and mechanical strength,which is utilized to construct candidate TE power generation and cooling devices near room temperature.Specifically,the effectiveness of band convergence,combined with optimized carrier concentration and electronic quality factor,distinctly boosts the Seebeck coefficient,thus greatly improving the power factor.Advanced electron microscopy observation indicates that complex multi-scale hierarchical structures and strain field distributions lead to ultra-low lattice thermal conductivity,and also effectively enhance mechanical properties.High ZT0.6 at 303 K,average ZTave1.18 from 303 to 553 K,and Vickers hardness of200 Hv in Ge0.78Cd0.06Pb0.1Sb0.06Te are obtained synchronously.Particularly,a 7-pair TE cooling device with a maximumΔT of45.9 K at Th=328 K,and a conversion efficiency of5.2%at Th=553 K is achieved in a single-leg device.The present findings demonstrate a unique approach to developing superior multifunctional GeTe-based alloys,opening up a promising avenue for commercial applications.

Effect of group-3 elements doping on promotion of in-plane Seebeck coefficient of n-type Mg_(3)Sb_(2)

Mg_(3)Sb_(2)-based alloys are promising thermoelectric materials with a reasonably low thermal conductivity.However,their electrical transport property is usually limited by the low carrier concentration.Mg_(3)Sb_(2) has a multi-valley conduction band with a six-fold degeneracy,benefiting n-type thermoelectric performance.Recently,n-type Y-doped Mg_(3)Sb_(1.5)Bi_(0.5) and Sc-doped Mg_(3)Sb_(2)-Mg_(3)Bi_(2) alloys show a large figure of merit(ZT).In this paper,the doping effect of group-3 and chalcogen elements on the electronic structures and electrical transport properties of Mg_(3)Sb_(2) was investigated via the first-principles calculations.Chalcogen elements have a slight effect on the electronic structure,and Te-doped Mg_(3)Sb_(2) shows better normalized power factors in both the out-of-plane and in-plane directions,compared to the Sdoped and Se-doped systems.Distinctly different doping effects appear in Mg_(3)Sb_(2) doped with group-3 elements.A increased density of states near the bottom of the conduction band can be induced by Sc or Y.Sc-doped and Y-doped Mg_(3)Sb_(2) show higher normalized power factors along the in-plane direction than those doped with chalcogens.

Pressure effects on the electrical transport and anharmonic lattice dynamics of r-GeTe:A first-principles study

Various strategies for thermoelectric material optimization have been widely studied and used for promoting electrical transport and suppressing thermal transport.As a nontraditional method,pressure has shown great potential,as it has been applied to obtain a high thermoelectric figure of merit,but the microscopic mechanisms involved have yet to be fully explored.In this study,we focus on r-GeTe,a lowtemperature phase of GeTe,and investigate the pressure effects on the electronic structure,electrical transport properties and anharmonic lattice dynamics based on density functional theory(DFT),the Boltzmann transport equations(BTEs)and perturbation theory.Electronic relaxation times are obtained based on the electron-phonon interaction and the constant relaxation time approximation.The corresponding electrical transport properties are compared with those obtained from previous experiments.Hydrostatic pressure is shown to increase valley degeneracy,decrease the band effective mass and enhance the electrical transport property.At the same time,the increase in the low-frequency phonon lifetime and phonon group velocity leads to an increase in lattice thermal conductivity under pressure.This study provides insight into r-GeTe under hydrostatic pressure and paves the way for a high-pressure strategy to optimize transport properties.