基于熵工程及SHS动力学的BiAgSeS本征低热导率起源探究

Unveiling the Intrinsic Low Thermal Conductivity of BiAgSeS through Entropy Engineering in SHS Kinetic Process

探索热电材料的超快速制备技术并优化其性能具有重要意义。本研究通过自蔓延高温合成技术快速制备得到BiAgSeS化合物。动力学过程研究表明,Bi熔化是激活并触发原料混合物发生自蔓延反应的关键,非平衡过程中产生的高浓度纳米及原子尺度应力应变区与螺旋位错为材料生长提供了永不消逝的台阶源,并在材料等离子体活化烧结致密化过程中进一步主导晶粒长大,最终在材料晶界处留下大量纳米孔洞。相比于传统熔融法结合等离子体活化烧结技术,本技术制备的材料的电导率略有提高,晶格热导率则下降约6%,最终材料ZT值在整个温区均有提高,并在773 K时取得最大值0.5。

It is of great significance to find the ultra-rapid preparation technology of materials and realize the optimization of electroacoustic transport properties in the research of thermoelectric materials.In this study,BiAgSeS compounds were successfully prepared by self-propagating high temperature synthesis(SHS),of which the kinetic process was systematically studied.It is found that the melting of Bi is the key to activate and initiate SHS reaction.In addition,the high concentrations of nano-and atomic-scale strain field regions,and screw dislocations produced in the non-equilibrium SHS process provide an everlasting step source for material growth and make the grains possess the layered structure.In the process of material densification,the step source continues to play a role in dominating grain growth,and thus leaving nanopores at the grain boundary.Because of these defects,compared with samples via melting-quenching(MQ)combined with plasma activated sintering(PAS),the SHS+PAS samples can slightly increase the electrical conductivity and significantly reduce the lattice thermal conductivity by~6%.Finally,the thermoelectric properties are optimized,and the ZT is improved in the whole temperature range with the maximum value of 0.5 obtained at 773 K.