SnSe+Ag_2Se composite engineering with ball milling for enhanced thermoelectric performance

Earth-abundant IV-VI semiconductor SnSe is regarded as a promising thermoelectric material due to its intrinsic low thermal conductivity. In this report, the highly textured SnSe/Ag2Se composites were first designed by solid solution method followed by spark plasma sintering （SPS） and their thermoelectric properties in two directions were investigated, and then, the performance of composites was further optimized with an additional ball milling. The coexistence of SnSe and Ag2Se phases is clearly confirmed by energy-dispersive X-ray spectroscopy （EDX） in transmission electron microscopy （TEM）. After ball milling, the size of SnSe grains as well as the incorporated Ag2Se particles reduces effectively, which synergistically optimizes the electrical and thermal transport properties at high temperature range. As a result, a maximum ZT of -0.74 at 773 K for SnSe ＋ 1.0%AgzSe in the direction vertical to the pressing direction is achieved. Composite engineering with additional ball milling is thus proved to be an efficient way to improve the thermoelectric properties of SnSe, and this strategy could be applicable to other thermoelectric systems.

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.

熵稳定热电材料

Thermoelectric technologies,which generate electricity directly from waste heat,have received considerable attention because of their potential to improve overall energy efficiency[1].The energy conversion efficiency is evaluated by a dimensionless figure-of-merit,defined as ZT=α^(2)σT/κ,whereα,σ,T,andκare the Seebeck coefficient,electrical conductivity,absolute temperature,and thermal conductivity,respectively.