Effects Of High Magnetic Fields On The Microstructures And Thermoelectric Properties Of Zinc Rich And Indium Doped ?-Zn₄Sb₃ Based Bulk Materials

Owing to its low thermal conductivity and a relatively high figure of merit,?-Zn4Sb3 has a wide application prospect in the field of intermediate-temperature thermoelectric materials.However,the figure of merit of ?-Zn4Sb3 are poor,it can not satisfy the needs of contemporary applications.Therefore,how to improve the thermoelectric properties of?-Zn4Sb3 has aroused widespresd interest.Elements doping and introducing the second phase can adjust the carrier concentration and mobility of materials,which are the effective strategies to improve materials'thermoelectric properties.In addition,it is well known that the microstructure of the materials can also affect their thermoelectric properties greatly.The high magnetic fields(HMFs)can affect the solute flow,solute element distribution,microstructure and so on by utilizing the Lorentz force,magnetization force,magnetic moment and magnetization energy,and it is expected to improve the performances of the thermoelectric materials.In this paper,In-doped and Zn-rich ?-Zn4b3 based thermoelectric materials were prepared by melt-cooling under HMFs.The effect of HMFs on microstructure and thermoelectric properties of Zn-rich and In-doped ?-Zn4Sb3 based thermoelectric materials were investigated.In this paper,phase composition and microstructure of the prepared ?-Zn4Sb3 based bulk materials were analyzed by metallographic microscope,X-ray diffraction analyses(XRD),Scanning electron microscopy-energy dispersives spectrometer(SEM-EDS)and Differential Scaunning Calorimetry(DSC),etc.Moreover,the thermoelectric properties(Seebeck coefficient,resistivity,thermal conductivity,carrier concentration and carrier mobility)of?-Zn4Sb3-based bulk materials were measured by using Seebeck coefficient/resistivity test equipment,Laser thermal conductivity and Hall effect tester.The conclusions are as follows:(1)Effects of HMFs on the microstructures and thermoelectric properties of Zn rich?-Zn4Sb3 based bulk materials:Zn-rich ?-Zn4Sb3 was composed of Zn4Sb3 and Zn,Zn was dispersed in the ?-ZnSb3 phase matrix,It is interesting that the HMFs can increased the dispersion of the Zn-rich phase in the ?-Zn4Sb3 matrix.After application of HMFs,the c axis was oriented parallel to the direction of the magnetic field.DSC results indicated that phase transition from ? to a transition shifted to a higher temperature.The Seebeck coefficient of lat%and 2at%Zn-rich ?-Zn4Sb3 decreased after applying HMFs,while 3at%Zn-rich?-Zn4Sb3 increased;furthermore,all of these samples prepared under HMFs had lower resistivity and thermal conductivity regardless of the Zn content.In general,HMFs had an effect of increasing the ZT value.The ZT value of the 2at%Zn-rich ?-Zn4Sb3 sample at 673K was 0.78 in the case of B=11.5T,an increase of 43.4%,compared to 0.54 under the magnetic field B=0T.(2)Effect of HMFs on the microstructures and thermoelectric properties of In doped?-Zn4Sb3 based materials:for the In-doped(X=0.005,0.02)?-Zn4Sb3 materials,the detection results showd that the samples were composed of Zn4Sb3 and Zn The Raman scattering results indicated that the application of HMFs enhanced the whole spectrum significantly and the spectrum shifted to the left.A high Seebeck coefficient of all the In-doped samples was obtained after the HMFs was applied,and also the resistivity.It made a result that the power factor of X=0.005 samples decreased while increased for the X=0.02 samples.(3)Effects of Zn-rich and In-doping on ?-Zn4Sb3:both Zn-rich and In doping can affect the carrier concentration and carrier mobility and then affect the electrical properties of the?-Zn4Sb3 deeply.Moreover,as a point defect in the crystal structure,the phonons can be effectively diffused to affect the thermal properties of the material In general,thermal conductivity and resistivity decreased with the increase of Zn content.Doping In increased the Seebeck coefficient and decreased the resistivity.The results of DSC show that In doping might restrain the transformation from ? phase to a phase.Morever,under the same HMFs,the power factor of all In-doped samples was higher than that of single-phase samples.