Preparation And Properties Of Filled CoSb₃ Based Thermoelectric Materials

With the rapid development of science and technology and global industrialization,the energy crisis has become more serious.Thermoelectric materials have great potential in the utilization of waste heat.The skutterudite CoSb3 based thermoelectric materials have become a promising thermoelectric material system due to their excellent electrical and mechanical properties,but their high thermal conductivity hinders their commercialization.In this paper,a series of Ybx(CoSb2.875Te0.125)4samples were prepared by vacuum melting and spark plasma sintering technology.After the XRD test,it was found that the peak position of the sample shifted to the left with the increase of Yb content,but the x=0.2 sample had a right shift phenomenon compared with the x=0.15 sample.It is speculated that the filling limit of Yb under Te doping is about 0.15?0.2.After Yb filling,the Fermi edge density and carrier concentration are increased,so that the Seebeck coefficient is increased and the conductivity is also increased.With the increase of the Yb filling amount,the scattering point position increases,and the low frequency local resonance generated by the thermal vibration interferes with the phonon transmission in the structure,thereby effectively reducing the lattice thermal conductivity.The ZT value of Yb0.2(CoSb2.875Te0.125)4sample reached 0.96 at most.Based on this,high-energry ball milling,pickling,nano-gold compounding,and annealing processes were improved.The study found that after high-energy ball milling,the lattice thermal conductivity was further reduced by increasing the grain boundary density and reducing the grain size.The high-density grain boundaries and interfaces increase the carrier transport barrier,which increases the Seebeck coefficient.After pickling,the oxide impurities in the sample are effectively removed,the scattering sites are reduced,and the conductivity is improved.The addition of nano-Au is conducive to the carrier transport at the grain boundary and improves the electrical conductivity.After annealing,the thermal expansion coefficients of the impurity phase and the matrix are different,resulting in an increase in porosity Impurity vapors(such as Te)at high temperatures in the pores dissipate a lot of heat,resulting in reduced thermal conductivity,and the thermal conductivity of the sample after annealing is reduced by about 60%.The low thermal conductivity allows the annealed sample to have a ZT value of 1.1 at 773k.PbS and CuS with high crystallinity and grain size around 50nm were synthesized by the water bath method;through testing,it was found that the Seebeck coefficient was improved due to the decrease in carrier concentration after recombination.The octahedral SnTe was prepared by hydrothermal method,and the Yb0.2(CoSb2.875Te0.125)4composite block with different SnTe content was prepared by mechanical ball milling,spark plasma sintering,and it was found that SnTe was not detected by XRD in the composite sample The second phase CoTe and CoTe2 are generated.The second phase increases carrier scattering,filters low-energy carriers,and increases the Seebeck coefficient.The maximum value is-223?V·K-1.Appropriate amount of SnTe compound also has a significant effect on hindering the heat conduction of Yb0.2(CoSb2.875Te0.125)4.The 3%SnTe/Yb0.2(CoSb2.875Te0.125)4 sample obtained a maximum ZT value of 1.18 at 773K.