Structure Refinement And Thermoelectric Properties Of Skutterudites

The skutterudite material has a relatively high power factor and excellent mechanical properties.It has great application potential in the field of medium-temperature thermoelectric materials.However,the higher lattice thermal conductivity has certain limitations on the improvement of the thermoelectric value.Therefore,on the basis of ensuring that the electrical properties of the skutterudite material do not decrease,reducing the thermal conductivity of the material can effectively improve the thermoelectric value of the skutterudite material.In this paper,phonon scattering is enhanced by introducing the second phase and scattering the grains to refine the crystal grains,thereby improving the thermoelectric value.Using XRD,SEM,conductivity/seebeck coefficient test system,laser thermal conductivity meter and other test systems,The effect of Si doping on the microstructure and thermoelectric properties of n-type Yb_0.3Co₄Sb₁₂skutterudite and refined grains for p-type Ce_0.45Nd_0.45Fe_3.5Co_0.5Sb₁₂skutterudite was investigated.The research results are as follows:For Si element doping n-type Yb_0.3Co₄Sb₁₂skutterudite,Slurry stripping combined with hot-press sintering preparation of materials.The introduction of Si element makes the conductivity of the material decrease,but the absolute value of the Seebeck coefficient increases,and the power factor slightly increases.In this experiment,the decrease of lattice thermal conductivity and electronic thermal conductivity is the main reason for the improvement of the thermoelectric figure of merit.The decrease in the lattice thermal conductivity is due to the fact that the second phase plays a role in enhancing phonon scattering,and the decrease in the electron thermal conductivity is caused by a decrease in the electrical conductivity due to a decrease in the actual Yb loading amount.When the temperature is 673 K,the thermal conductivity of undoped Si and Si doped 0.1 are 3.66 W m^-11 K^-1and 3.01 W m^-11 K^-1,respectively.At this time,the reduction rate reached 17.76%.The samples with undoped Si and doped 0.1 Si have a thermoelectric figure of merit of 1.14 and 1.32 at823 K,respectively.The improvement of the thermoelectric figure of merit is about15.79%.The introduction of Si element in the Yb_0.3Co₄Sb₁₂skutterudite to form the second phase,on the basis of ensuring that the electrical properties are not reduced,realizes the reduction of the thermal conductivity of the material and improves the thermoelectric value of the material.For the p-type Ce_0.45Nd_0.45Fe_3.5Co_0.5Sb₁₂2 skutterudite,the material was prepared by two processes,namely,melting spin,combined with hot-press sintering,annealing and hot-press sintering.By comparison,it was found that the sample prepared by the stripping process has multi-scale micro-nano structures,and the grain size of the sample is lower than that of the annealing process sample.The electrical properties of the material are not significantly improved,but the smaller grain size results in a greater reduction in the lattice thermal conductivity of the material.At 673 K,the lattice thermal conductivity of the samples prepared by the stripping and the lattice thermal conductivity of annealed samples were 0.53 W m^-11 K^-1and 0.65 W m^-11 K^-1,respectively,and the lattice thermal conductivity decreased by 18.46%.When the temperature is 783 K,the thermoelectric properties obtained by the two processes are1.2 and 1.06,respectively,and the increase rate is 13.2%.