Study On The Enhancement Mechanism Of Energy Band And Microstructure Regulation On The Thermoelectric Performance Of Cu_1.8S Bulk Materials

Thermoelectric material is a new type of energy material that enable direct conversion between heat and electricity.Nowadays,traditional energy sources are drying up,the greenhouse effect and environmental pollution need to be controlled in the meantime.Thermoelectric devices with thermoe lectric materials as the core components possess lots of advantages like stable,no moving parts,no noise,no pollution,which owns broad application in industrial waste heat recovery,waste heat power generation and semiconductor refrigeration.Therefore,the development of thermoelectric materials attracts extensive attention currently.The copper sulfide,a kind of medium-high temperature thermoelectric materials,was studied in this paper.Compared with the traditional high-performance thermoelectric materials,it possesses the advantages of environmental friendliness,low toxicity,low price of raw material and wide element distribution.Whereas the thermoelectric performance of copper sulfide materials still needs to be improved.This paper mainly focuses on the p-type Cu_1.8S thermoelectric material,combining with mechanical alloying?MA?and spark plasma sintering?SPS?techniques to prepare C u1.8S-based polycrystalline bulk thermoelectric materials.The thermoelectric properties of C u1.8S materials have been optimized through band structure and microstructure adjustment by introducing other sulfides.O n the one hand,the doping has been achieved through introducing sulfides materials for improving carrier concentration and adjusting band structure.O n the other hand,the microstructure of Cu_1.8S has been also changed by adding sulfides,which results in introducing phonons scattering centers to reduce the thermal conductivity.The thermoelectric performance has been enhanced as last.At present,few studies has been proved on the thermoelectric properties of C u1.8S material composition.There is still a lack of theoretical research on how and which materials to introduce in C u1.8S for improving thermoelectric performance.More experimental results sho uld be done to assist to complete the database.In this paper,by directly adding other second phase of sulfide in the MA process,the Na2 S,core-shell structure Bi/Bi2S3,Pb S,In2S3 doped Cu_1.8S materials was prepared.The effects of various sulfides on the band structure and microstructure adjustment of Cu_1.8S materials were studied,and the enhancement mechanism of thermoelectric properties was explored.According to the experimental results,the porous C u1.8S bulk material could be synthesized by introducing 2 wt% Na2 S,the thermal conductivity is thus significantly decreased.The ZT value reaches 0.77 at 773 K,which is higher than that of p-type Cu_1.8S material.In addition,benefiting from the energy filtering effect by doping core-shell structure Bi/Bi2S3,the Seebeck coefficient is optimized and ZT value of the Cu_1.8S material reaches 0.77 at 723 K.Besides,the introduction of Pb S in C u1.8S introduced point defects and chain-like nanopores,which resulted in a ZT value of 1.1 for the material at 773 K.We also found that the introduction of In2S3 not only enables the In doping of Cu_1.8S,but also generate the special nanostructure.Finally,the ZT value of the material reaches 1.4 at 773 K,which is 2.9 times higher than that of the pure Cu_1.8S.