The Improvement Of The Performance Of SnTe-Based Thermoelectric Materials Through Adjusting The Energy Band Structure And Phonon Scattering

At present,the contradiction between energy supply and ecological environment is more and more prominent,vigorously developing green energy is an effective measure to solve this contradiction.As a kind of green energy material,thermoelectric material has attracted more and more attention because of its ability to convert waste heat directly into electricity.PbTe,as a kind of thermoelectric material with high performance,has been successfully applied in some fields.However,due to the threat of Pb element to the environment,it has been hindered in the wide range of popularization.As a lead-free thermoelectric material,SnTe has attracted interest in recent years because of its similar lattice and band structure to PbTe.However,intrinsic SnTe shows poor thermoelectric performance.The main reasons can be attributed to:first,due to the presence of the inherent Sn vacancy,it has high carrier concentration(1020?1021cm-3),which leads to a low Seebeck coefficient and a high electron thermal conductivity.Second,Small band gap(0.18eV at 300 K)and large energy separation(0.35eV at 300 K)between the light and heavy valence bands in SnTe material,make the dual-polarization phenomenon appear too early and the heavy valence bands are difficult to participate in the thermoelectric transport.In view of the above shortcomings,the band structure and phonon scattering are adjusted by doping elemental elements and nano-alloys to improve the performance of SnTe based thermoelectric materials.The specific research work of this paper is as follows:1.The effect of co-doping of Pd-In on the properties of SnTe based thermoelectric materials was studied.The results show that the existence of Pd can introduce valence band convergence effect,and the existence of In elemental elements can introduce energy level resonance effect in the matrix.The co-doping of Pd-In can improve the thermoelectric performance of SnTe by adjusting the band structure.In addition,the effect of local phase transition on the thermal conductivity of materials is also revealed by neutron scattering and synchrotron radiation experiments.Finally,the maximum ZT value of sample Sn0.98Pd0.025In0.025Te reached 1.51 at 800K.2.The effect of co-doping of MgAgSb and In elemental elements on the properties of SnTe was investigated.For SnTe,MgAgSb is a special alloy.The diffusion of Mg,Ag,and Sb elements can introduce valence band convergence into the matrix to optimize the electrical properties of the material.Except for band convergence,any of the diffused elements from MgAgSb could enter into the Sn vacancies and reduce the hole concentration.Thus,the combination with In elemental elements can introduce a complete band engineering to adjust the band structure in SnTe.In addition,the size distribution of the MgAgSb nano-alloy ranges from several nanometers to several micrometers,which can introduce full-scale phonon scattering to reduce the lattice thermal conductivity.Finally,the maximum ZT value of sample Sn1.02In0.025Te-3%MgAgSb reached 1.41 at 835K.Moreover,the doping of nano-alloy can effectively improve the mechanical properties of SnTe and further increase their working temperature peak,which is of great significance to the practical application of materials3.The effect of the core-shell structure formed by BiCuSeO nano-alloy doping on the properties of SnTe was studied.The results show that the BiCuSeO nanoalloy in SnTe substrate forms a SnO2 coating layer at the interface during the high-temperature solid-phase reaction process,thus forming the BiCuSeO@SnO2 core-shell nanostructure.The BiCuSeO@SnO2 core-shell nanostructure leads to a large number of heterogeneous interfaces,which can introduce multiple potential barriers to enhance the energy filtering effect.Compared with the undoped samples at room temperature,the enhanced energy filtering effect can significantly improve the hall mobility and significantly reduce the carrier concentration.In addition,the core-shell nanostructure act as a scattering center for phonons to reduce lattice thermal conductivity.Finally,the maximum ZT value of the Sn1.03Te 5%BiCuSeO sample reached 1.21 at 835K.