Investigation On Properties Of SnTe Based Thermoelectric Nanocomposites Prepared By In-Situ Reaction Method

Thermoelectric material is a clean and renewable new energy material that can directly convert electric energy into heat energy.It has broad application prospects in the field of waste heat utilization.PbTe-based compounds have long been considered as the leading thermoelectric materials for the mid-temperature,but the toxicity of Pb limits its wide application.Due to the non-toxic and rich elements and similar crystal structure and band structure with PbTe,SnTe compounds are considered to be a promising alternative material for the mid-temperature.However,its ultrahigh carrier concentration and the large thermal conductivity leads to a low ZT value of SnTe.Thereby,in this thesis,through the point defect engineering and nanostructure design,the disproportionation reaction of SnO and the addition of Cu₂Se are applied to regulate the carrier concentration and lattice thermal conductivity of SnTe,and finally a significant enhancement of the thermoelectric performance of SnTe compound have been achieved.The main contents and results of the investigations are summarized as follows:The effect of SnO addition on the phase composition,microstructure and thermoelectric properties of SnTe has been studied.The SnTe-xmol%SnO samples were prepared by the high-temperature vacuum melting method combined with ball milling and hot-pressing sintering process.The Sn self-doping and the in-situ composite of SnO₂nanophase was realized simultaneously by the disproportionation of SnO during the process of the hot-press sintering.On the one hand,the self-doping of Sn significantly reduces the carrier concentration and electron thermal conductivity,and increases the power factor.On the other hand,in-situ generated SnO₂ nanoparticles are dispersedly distributed on the grain boundaries,leading to the multiscale phonon scattering and the reduced lattice thermal conductivity.When the content of SnO is 6 mol%,the ZT value of SnTe reaches 0.96 at 873K,a¹00%enhancement compared with that of the pristine SnTe.The influence of Cu₂Se addition on the phase composition,microstructure and thermoelectric properties of SnTe has been investigated.The?SnTe?_1-x?Cu₂Se?_x samples were prepared by the high temperature vacuum melting-quenching method and hot pressing sintering process.The in-situ composite of Cu₇Te₄ nanophase was realized by the introduction of Cu₂Se.Cu₂Se and SnTe undergoes a displacement reaction during high-temperature vacuum melting,in which Se^2-replaces Te^2-atoms,and a small amount of Cu⁺replaces Sn²⁺,in-situ generating Cu₇Te₄ nanoparticals are dispersedly distributed along the grain boundary.These nanoparticles together with a large amount of the Se_Te and Cu_Sn'point defects and the stacking faults significantly reduced the lattice thermal conductivity of the samples,approaching the amorphous limit of SnTe.As a result,the maximum ZT value of1.02?⁸0%improvement compared with that of the pristine SnTe?at 873 K is achieved for the sample?SnTe?_0.97?Cu₂Se?_0.03.