Effects Of High Magnetic Fields On The Microstructures And Thermoelectric Properties Of β-Zn₄Sb₃ Bulk Material

is one of the promising intermediate temperature thermoelectric materials. Comparing to the PbTe, β-Zn4Sb3has the advantages such as low cost and non-toxic. More importantly, β-Zn4Sb3 has extremely low thermal conductivity which leads to its excellent thermoelectric performance. Presently, researchers are still focused on finding a way to effectively improve the thermoelectric properties of β-Zn4Sb3. High magnetic field can control the microstructures of materials by utilizing the Lorentz force, magnetic force and magnetic torque. Therefore, it is very likely that thermoelectric properties can be improved by the high magnetic fields. In the work, β-Zn4Sb3 bulk materials were prepared by using the melting and slowing process under high magnetic fields. Moreover, the effects of high magnetic fields on microstructures and thermoelectric properties of β-Zn4Sb3 bulk materials were investigated.In this paper, thermoelectric properties (Seebeck coefficient, resistivity, thermal conductivity, carrier concentration and mobility) were measured. Moreover, phase composition and microstructure were characterized by XRD, SEM-EDS and HR-TEM. Furthermore, effects of high magnetic fields on the Zn vacancy were also studied by using the DSC and Rietveld refinement. Conclusions can be reached as follow:(1) Samples prepared under high magnetic fields had lower resistivity, Seebeck coefficient, thermal conductivity and higher carrier concentration. The highest ZT value (ZTmax= 0.97) was obtained for the B= 8.8 T sample at the temperature of 673 K. Comparing to the sample prepared without magnetic field (Zrmax=0.88), the imposition of high magnetic fields can lead to 10% enhancement of the ZTmax value.(2) Nanovoids uniformly dispersed in the sample which prepared without high magnetic field. With the imposition of high magnetic fields, the nanovoids disappeared. Moreover, Zn-rich nanoparticles with larger size segregated in the grain boundary and Sb-rich nanoparticles with smaller size formed in the grain interior. Besides, the results of DSC and Rietveld refinement showed that the high magnetic field can increase the Zn vacancy.(3) For the samples prepared under high magnetic fields, Zn-rich nanoparticles segregated in the grain boundary. Therefore, carrier concentration in the grain boundary was much higher than that of the grain interior. Thus, carriers will be injected into the grain interior and lead to the increase of carrier concentration of the sample. Moreover, Zn vacancies were increased due to segregation of Zn-rich nanoparticles. Since the Zn vacancy is the origin of the p-type conducting of the β-Zn4Sb3, thus the amount of Zn vacancy can greatly influence the carrier concentration. Based upon the results of DSC and Rietveld refinement, high magnetic fields increased the Zn vacancy of the sample thus lead to the increase of carrier concentration. Furthermore, Zn vacancy is also a kind of point defects which can scatter phonons. Therefore, the increase of Zn vacancy can also contribute to the decrease of thermal conductivity.