| In the 21 st century,with the increasing global energy demands and the growing environmental problems,the governments are actively looking for more new clean energy resources and researching for new energy conversion technologies.Among them,the thermoelectric technology is a good way to convert thermal energy to electric energy by the Peltier effect and the Seebeck effect.Thermoelectric device has high reliability,small size,no noise,no pollution,no moving parts etc,so that it becomes eye-catching research field of the world in recent years.The core of thermoelectric conversion technology is to explore thermoelectric materials with high conversion efficiency.Among them,In4Se3 based-compounds are new promising low-dimensional thermoelectric materials.Because its layered structure characteristics lead to low thermal conductivity,In4Se3 based-compounds potentially achive high thermoelectric performance.According to the work by Jong-Soo Rhyee,a South Korea scientist,in2011,the ZT value of the In4Se3-xClx single crystal on the b-c plane has reached 1.53 at698 K by enhancing the carrier concentration and mobility.However,the synthesis process of single crystal is complicated and expensive,and the product has obvious anisotropy.Moreover,it is easy to dissociate along the interlayer,resulting in poor mechanical properties which is not conducive to the future industrial market.In 2013,Wu achieved the high performance of polycrystalline In4SnxPbySe3 by co-doping Pb/Sn,and the optimal value ZT is 1.4 at 733 K.Therefore,to further investigate the thermoelectric propertices of In4Se3 polycrystalline is very meaningful.However,the key parameters of thermoelectric performance such as the thermal conductivity ? ?electric conductivity ? and power factor PF are strongly coupled,which is not conducive to the optimization of ZT value.Therefore,the independent tuning of thermoelectric parameters is an effective method to further optimize the thermoelectric performance.In this work,we adopted the single doping and co-doping elements to synthesize In4Se3 polycrystalline ingot by solid reaction solution combined with the method of spark plasma sintering(SPS).Then the thermal and electrical transport performance were tested,and the thermoelectric properties of In4Se3 system were analyzed by XRD and SEM combining with electronic structure calculation.We have investigated the effects of different dopants on the thermoelectric properties of In4Se3 system.Finally,the thermoelectric parameters can be preliminary independently tuned and we realize the improvement of thermoelectric performance.The main work as follows:(1)In4Se3 bulk material was successfully prepared by solid reaction synthesis method combined with spark plasma sintering(SPS).The XRD pattern analysis showed that the obtained samples were pure-phase materials.Band structure calculation indicated it is a narrow gap semiconductor with gap about 0.4ev.The microstructure characterization by scanning electron microscopy(SEM)shows that it has layered structure.The thermoelectric properties test shows that it is an n-type semiconductor material with a low thermal conductivity.At 720 K,the ZT value reaches 0.65,which indicates that the In4Se3 material has both potential research significance and application value in the middle temperature region.(2)In4-xCexSe3(x =0,0.03,0.06,0.1)was successfully synthesized by solid reaction synthesis and spark plasma sintering(SPS)technology,and the samples were measured for thermoelectric properties.The thermal conductivity of the material is further reduced,and the Seebeck coefficient and the electrical conductivity do not change at all.The independent tuning of the thermoelectric parameters is realized,which lays the foundation for the follow-up experimental research.(3)In4-xCexPb0.01Se3(x=0.03,0.06,0.08,0.1)was synthesized by solid reaction synthesis and spark plasma sintering(SPS)technology on the basis of In4-xCexSe3(x=0.03,0.06,0.08,0.1),and the quantitative of the Pb element was doped in the In4-xCexSe3.Under the Ce and Pb co-doping,the low thermal conductivity of the In4-xCexPb0.01Se3 material is kept.At the same time,the conductivity and power factor are greatly improved.Finally,the ZT value reaches 1.1 at 710 K,achieving 67%enhancement compared with pristine In4Se3 materials. |
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