Thermoelectric Properties Of SnTe Based Materials Controlled By Doping And Nanocomposite

Thermoelectric materials have the advantage of reversible conversion between heat and electricity,and are widely studied by researchers.Among the thermoelectric materials in the middle temperature region,Pb Te alloy materials have higher thermoelectric value and better thermoelectric performance,but its large-scale application is hindered by factors such as poor stability of Pb Te at high temperature and environmental pollution caused by Pb volatilization.Researchers found Sn Te alloy and Pb Te crystal structure of the alloy,the same type of Na Cl cubic rock salt structure,at the same time,the band structure similar,therefore the thermoelectric performance of Sn Te base material is also good,and Sn Te environmentally friendly,non-toxic harmless,and lower cost,become a kind of potential environmental friendly and performance of thermoelectric materials,Researchers are increasingly concerned.Due to the intrinsic Sn vacancy in Sn Te crystal,the concentration of hole carriers in its lattice is very high,resulting in high electronic thermal conductivity and low Seebeck coefficient,so the thermoelectric performance of Sn Te alloy is poor.Process in this paper,the operation is simple and controllable step is opposite with the preparation of the discharge plasma sintering process,the first step to the introduction of low content and non-toxic Ge and Bi doped double elements,carrier energy band engineering and engineering to improve the electrical transport properties of Sn Te,reduce the electron thermal conductivity,heterogeneous atoms can affect the microstructure,introduced at the same time,The thermal conductivity of Sn Te alloy was reduced,and the thermoelectric properties of Sn Te alloy were comprehensively optimized.In the second step,Ag Bi Te₂ nano phase was introduced into the Sn Te double-doped system,and phonon engineering was used to enhance phonon scattering in various frequency bands in the lattice,so as to further optimize the performance of Sn Te thermoelectric materials.The main conclusions of this paper are as follows:（1）Ge and Bi dual-element doped Sn Te bulk sample materials were prepared by one-step solid-state reaction and discharge plasma sintering with simple operation and controllable process.By doping Bi element,Sn²⁺is replaced by Bi³⁺ion,and the excess electrons carried by Sn2+can compensate for the higher intrinsic level of tin holes,reduce the carrier concentration,improve the band structure of the sample,and improve the Siebeck coefficient and power factor.Ge and Bi element doping will introduce a large number of diatomic point defects,which can better inhibit carrier migration,enhance the local force of phonon,and promote the reduction of lattice thermal conductivity.The thermoelectric performance of Sn Te material was improved by optimizing the material from both electrical and thermal aspects.At 873K,the thermoelectric optimum value of Sn_0.92Ge_0.04Bi_0.04Te sample reached 0.83,which was greatly improved compared with 0.33 of pure Sn Te.（2）On the basis of the above work,the preparation process of one-step solid phase reaction and spark plasma sintering,which is simple and controllable,is continued to introduce the second phase of silver-rich nanometer Ag Bi Te₂ into the Sn_0.92Ge_0.04Bi_0.04Te double-doped system.The study shows that the introduction of the second phase of nanometer Ag Bi Te₂,The Ag element further regulates the band structure of the sample material,and the point defect and Ag Bi Te₂ nanometer second phase enhance the phonon scattering of each frequency band in the lattice,greatly reducing the lattice thermal conductivity of the material,realizing the cooperative optimization of the thermoelectric properties of Sn Te material,thus greatly improving the thermoelectric properties of Sn Te material.This makes it possible for the wide application of environmentally friendly high-performance Sn Te thermoelectric materials.