Doping Modification And Thermoelectric Performance Optimization Of SnTe-based Alloy

Group IV-VI compound SnTe alloy has non-toxic elements,good mechanical properties and simple preparation process.It is a kind of environment-friendly middle-temperature thermoelectric material with great application potential.However,the intrinsic carrier concentration of SnTe alloy is relatively high,and the energy offset between the L-band and the?-band is relatively large,resulting in a small low-temperature Seebeck coefficient,high lattice thermal conductivity,and poor thermoelectric performance.In this paper,energy band engineering and multi-scale defect control are used to improve the power factor of SnTe alloy and reduce the lattice thermal conductivity.Using smelting-quenching-annealing process,combined with hot pressing sintering to prepare samples,using X-ray diffractometer,scanning electron microscope,transmission electron microscope,electrical performance parameter testing instrument,laser thermal conductivity meter,Hall effect measurement system and other equipment research the effect of co-doping Bi-Mn and Sb-Mn at the Sn site on the phase composition,microstructure and electrothermal transport characteristics of SnTe alloys.The band structure and microstructure analysis and the Debye-Callaway model are used to find out the electrothermal transport mechanism,reveal the doping modification mechanism.The study found that smelting-quenching-annealing process introduces high-density dislocations in the Sn_1-3xBi_xMn_2xTe alloy,and at the same time,Mn doping reduces the solid solubility of Bi in the SnTe alloy.Bi is mainly precipitated in the form of the elementary second phase,with a size between a few hundred nanometers and a few microns.Mn doping makes SnTe alloy energy bands converge,increases energy valley degeneracy,and improves the alloy's Seebeck coefficient;At the same time,point defects and high-density dislocations enhance the scattering of phonons and reduce the alloy's lattice thermal conductivity.The average power factor and average ZT value of Sn_0.85Bi_0.05Mn_0.1Te alloy in the range of 300 K-873 K are 16.36?Wcm^-1K^-2 and0.72,respectively.Compared with undoped SnTe alloy,the increase was 57.5%and 213%respectively.The research results show that the co-doping of Sb-Mn makes the Sb-rich nano-second phase formed in the Sn_1-3xSb_xMn_2xTe alloy,which enhances phonon scattering and reduces the mean free path of phonons.The lattice conductivity of Sn_0.76Sb_0.08Mn_0.16Te alloy at 873 K reduces to 0.54 Wm^-1K^-1.At the same temperature,with the increase of doping content,the electrical conductivity and thermal conductivity of Sn_1-3xSb_xMn_2xTe alloy decrease,and the carrier concentration and Seebeck coefficient increase.When x=0.06,the average power factor and average ZT values of the alloy in the range of 300 K-873 K are about 18.75?Wcm^-1K^-2 and 0.73,respectively,at arm length L=2mm,and the temperature at the hot and cold ends are 300 K and 873 K,respectively,the theoretical maximum output power density and conversion efficiency of the alloy are 7.67 Wcm^-2 and 11.29%,respectively.