The Effect Of Electric Field On The Microstructure And Thermoelectric Performance Of Bi-Sb-Te And Mg-Si-Sn

Facing the worldwide energy crisis and environmental pollution which seriously threaten the survival and development of mankind, researchers from all over the world are working at exploring alternatives to fossil energy. For our country, development of new and renewable energy has been established as national strategy in the "twelfth five-year plan". As a promising green energy resource, thermoelectric conversion technology has been given great attention.Thermoelectric materials are kind of functional material which can convert heat to electricity directly or reversely. Due to the advantages such as small-size, high-reliability, long-lifetime and pollution-free, thermoelectric materials are of interest for applications as cooling devices and power generator used in craft or recycling of the industrial waste heat.Characterized by the applying of electric current to assist or activate the sintering process, faster heating rate and lower sintering temperature over conventional sintering methods, electric current activated pressure assisted sintering (FAPAS) technology has been introduced into the preparation of thermoelectric materials and has been proved to be helpful of acquiring better thermoelectric performance. However, the intrinsic role of electric current in the sintering process of thermoelectric materials needs to be further explored.In the present study, the FAPAS process was modified. Different processes were applied in the sintering of Bi1.2Sb4.8Te9 and Mg2Sio.8Sno.2 thermoelectric materials. Finite element analysis was used to investigate the distribution of electric current and temperature in the sintering processes. The effects of electric current on the microstructure and thermoelectric performance were explored.The results demonstrate that the applying of electric current in the sintering process can significantly improve the uniformity and density of Bi1.2Sb4.8Te9 and Mg2Si0.8Sn0.2 thermoelectric materials. When applying current of high intensity, preferred orientation of grains was observed in the Bi1.2Sb4.8Te9 sample. For the Mg2Sio.8Sno.2 samples, the applying of electric current in the sintering process can promote the formation of solid solution and form river pattern in the cross section parallel to the current direction, which indicate that the applying electric current in the sintering process could enhance the mass migration along the current direction.Moreover, positive effect of applying electric current in the sintering process of Bi1.2Sb4.8Te9 and Mg2Si0.8Sn0.2 thermoelectric materials on the electrical properties has also been confirmed. For Bi1.2Sb4.8Te9, applying electric current in the sintering process can contribute to acquiring both higher electric conductivity and Seebeck coefficient. By applying high intensity of electric current in the sintering process, both high electrical properties and low thermal conductivity could be acquired. The maximum ZT values of the samples applied with none, low intensity and high intensity of electric current are 0.46,0.48 and 0.57, respectively. For Mg2Sio.8Sno.2, applying electric current in the sintering process can contribute to acquiring much higher electric conductivity and power factor. The power factor of the samples applied with low and high intensity of electric current are higher by a factor of 1.17×10-3 Wm-1 K-2 and 1.28×l0-3 W m-1K-2 than the sample applied with none electric current.