Optimization of the average figure-of-merit zT in medium-entropy GeTe-based materials via entropy engineering

Entropy engineering has emerged as an effective strategy for improving the figure-of-merit zT by decelerating the phonon transport while maintaining good electrical transport properties of thermoelectric materials.Herein,a high average zT of 1.54 and a maximum zT of 2.1 are achieved in the mid-entropy GeTe constructed by Ag,Sb,and Pb alloying.At room temperature,the mid-entropy GeTe tends to be a cubic structure.And the power factor is improved from 7.7μW·cm^(-1)·K^(-2) to 16.2μW·cm·cm^(-1)·K^(-2) due to the large increase in effective mass and the optimized carrier concentration.The increasing disorder created by heavy and off-centering Ag,Sb,and Pb atoms induces strong mass/strain fluctuations and phonon scattering to decelerate the phonon transport in GeTe.A low lattice thermal conductivity is obtained in the medium-entropy GeTe-based material.Moreover,a GeTe-based thermoelectric cooler is fabricated with the cooling temperature difference of 66.6 K with the hot end fixed at 363 K.This work reveals the effectiveness of entropy engineering in improving the average zT in GeTe and shows potential application of GeTe as a thermoelectric cooler.

Entropy engineering in inorganic non-metallic glass

Advances in developing high entropy alloys and ceramics with improved physical properties have greatly broadened their application field from aerospace industry,public transportation to nuclear plants.In this review,we describe the concept of entropy engineering as applicable to inorganic non-metallic glasses,especially for tailoring and enhancing their mechanical,electrical,and optical properties.We also present opportunities and challenges in calculating entropy of inorganic non-metallic glass systems,correlating entropy to glass formation,and in developing functional inorganic non-metallic glasses via the entropy concept.

Maximizing the scattering of multiwavelength phonons in novel biphasic high-entropy ZrCoSb-based half-Heusler alloys

The thermoelectric(TE)performance of p-type ZrCoSb-based half-Heusler(HH)alloys has been improved tremendously in recent years;however,it remains challenging to find suitable n-type ZrCoSb-based HH alloys due to their high lattice thermal conductivity(κ_(L)).In this work,n-type Zr_(1−x)Ta_(x)Co_(1−x)Ni_(x)Sb HH alloys were firstly designed by multisite alloying.The evolution of the Raman peak proved that alloy scattering,phonon softening,anharmonicity,entropy-driven disorder,and precipitates had a combined effect on decreasingκ_(L)by 46.7%compared to that of pristine ZrCoSb.Subsequently,Hf_(0.75)Zr_(0.25)NiSn_(0.99)Sb_(0.01)was introduced into Zr_(0.88)Ta_(0.12)Co_(0.88)Ni_(0.12)Sb to further suppressκ_(L).Remarkably,the grain size of the biphasic HH alloys was refined by at least one order of magnitude.A biphasic high-entropy HH alloy with y=0.2 exhibited the minimumκ_(L)of∼2.44 W/(m·K)at 923 K,reducing by 67.7%compared to that of ZrCoSb.Consequently,(Zr_(0.88)Ta_(0.12)Co_(0.88)Ni_(0.12)Sb)_(0.9)(Hf_(0.75)Zr_(0.25)NiSn_(0.99)Sb_(0.01))_(0.1)exhibited the highest TE figure of merit(∼0.38)at 923 K.The cooperation between the entropy and biphasic microstructure resulted in multiscale defects,refined grains,and biphasic interfaces,which maximized the scattering of the multiwavelength phonons in HH alloys.This work provides a new strategy for further reducing the grain size andκ_(L)of medium-and high-entropy HH alloys.

Cu_(1.8)S基合金的热电性能和电稳定性增强:熵工程和Cu空位工程

无污染、低成本和高性能Cu_(1.8)S基类液态热电材料受到关注.但是,其过高的本征Cu空位和Cu离子迁移特性限制了其性能和电稳定性的进一步提升.本研究采用机械合金化结合放电等离子体烧结制备了一系列Cu_(1.8)S和Mn_(x)Cu_(1.8)S_(0.5)Se_(0.5)(0.01≤x≤0.06)块体热电材料.随着Se和Mn的引入,体系由低熵Cu_(1.8)S(0.4R^(*))转变为中熵MnxCu_(1.8)S_(0.5)Se_(0.5)(1.2R^(*)).构型熵的增加不仅提高了体系的结构对称性,MnxCu_(1.8)S_(0.5)Se_(0.5)室温下呈立方相结构,还增大了Mn的固溶度.高浓度Mn固溶有效填补了过高的本征Cu空位,降低了载流子浓度,优化了能带结构,提升了电输运性能.熵工程一方面增大了Cu离子迁移势垒,抑制Cu离子迁移.750 K下,即使电流密度达到24 A cm^(-2),Mn_(0.03)Cu_(1.8)S_(0.5)Se_(0.5)的电阻也几乎没有变化,显示出优异的电稳定性;同时可降低声速,软化晶格,降低晶格热导率.Mn_(0.06)Cu_(1.8)S_(0.5)Se_(0.5)的块体样品在773 K时获得最大ZT值0.79,相较于初始样品提高了两倍.结果表明熵工程结合Cu空位工程是提升Cu_(1.8)S基热电材料性能的有效策略.