Preparation And Properties Study Of BiCuSeO And Cu₃SbSe₄ Based Thermoelectric Materials

Thermoelectric materials are functional materials based on the thermoelectric effect,using the movement of carriers（holes or electrons）inside the material to achieve the conversion between thermal and electrical energy,and have broad application prospects in fields such as thermoelectric temperature difference power generation and solid state refrigeration.In recent years,the application of thermoelectric materials for industrial waste heat recovery and thermal management has received a lot of attention from researchers due to the energy crisis and increasing environmental pollution.The natural superlattice structure of BiCuSeO and the typical ternary Cu-based compound Cu₃SbSe₄ have the advantages of being earth-rich in constituent elements,low cost,non-toxic and environmentally friendly,both of which are very promising materials for thermoelectric conversion with potential applications today.The low intrinsic conductivity due to the low carrier concentration limits the development and utilisation of BiCuSeO and Cu₃SbSe₄.Therefore,it is of great importance to carry out research on BiCuSeO and Cu₃SbSe₄thermoelectric materials.In view of this,BiCuSeO and Cu₃SbSe₄ were selected for this thesis,and BiCuSeO-based and Cu₃SbSe₄-based thermoelectric materials were systematically investigated through experiments.Multi-scale defects such as point defects,dislocations and grain boundaries were introduced within both materials by means of multi-element doping to achieve synergistic optimisation of power factor and lattice thermal conductivity,ultimately leading to a jump in thermoelectric properties.The main research elements and results are as follows:（1）To investigate the effect of Al/La/Sb/Y/Ca multi-element co-doping on the microstructure and thermoelectric properties of BiCuSeO.Bi_1-3x-y-zAl_xLa_xSb_xY_yCa_zCuSeO ceramic samples were prepared by high-energy ball milling and cold isostatic pressing methods.The doping of Al/La/Sb/Y/Ca resulted in a significant increase in the carrier concentration of the system,which led to an increase in conductivity,a decrease in Seebeck coefficient and an increase in power factor.The multi-element doping leads to a complex material microstructure,resulting in a reduction in the lattice thermal conductivity of the system from 0.45 Wm^-1K^-1 to 0.23 Wm^-1K^-1（773 K）.Further increase in Ca element doping significantlyincreasedthecarrierconcentrationofthe Bi_0.92-xAl_0.02La_0.02Sb_0.02Y_0.02Ca_xCuSeO system,obtaining a larger power factor.At 773 K,the ZT_max of the Bi_0.82Al_0.02La_0.02Sb_0.02Y_0.02Ca_0.10CuSeO sample was～1.24,nearly five times that of the BiCuSeO sample（0.25）.The experimental results show that Ag/Fe and Ag/Bi double doping achieves a simultaneous increase in conductivity and Seebeck coefficient.（2）A series of Cu₃SbSe₄ ceramic samples were prepared by solid-phase synthesis（vacuum melting+cold isostatic pressing）and the effects of Bi/Fe,Ag/Fe,Ag/Bi double-doping and Ag/Bi/Fe co-doping on the thermoelectric properties of Cu₃SbSe₄ were investigated.At the same time,doping reduces the grain size,introduces multi-scale defects,modulates the phonon mean free range and reduces the lattice thermal conductivity of the material.At 573 K,the ZT maximum for the Cu_2.85Ag_0.15Sb_0.985Bi_0.015Se₄ sample was 0.38.Further Pb replacement of Sb elements was used to enhance the thermoelectric properties of Cu_2.85Ag_0.15Sb_0.985-xBi_0.015Pb_xSe₄samples.At 573 K,the ZT value for the Cu_2.85Ag_0.15Sb_0.935Bi_0.015Pb_0.05Se₄ sample was a maximum of 0.46,which was 3.3 times higher than that of Cu₃SbSe₄（～0.14）.