Effects Of Melt Treatment Of Bi-Te Based Thermoelectric Materials On Microstructure And Property

The Bi-Te based material is one of the optimal materials with the highestthermoelectric property at room temperature among the known thermoelectricmaterials, and it is widely used in the commercial power-generation devices. Toenhance the performance of thermoelectric materials, therefore, one of the main resortsis to ameliorate preparation technologies, for instance, zone melting, spark plasmasintering, microwave sintering, and hot pressing. However, the methods mentionedabove have drawbacks, such as high production cost and complicated productionprocedures. Few people pay attention to the effects of melt status in the preparation ofBi-Te based material on solidification microstructure and thermoelectric property.The temperature dependence of electrical resistivity of molten p-type thermoelectricalloys (BiXSb1-X)2Te3(X=0.3,0.4,0.5) were explored by DC four-electrode methodin this paper. And the possibility of melt structure transition, reversibility, andtemperature ranges were then investigated. Based on this judgement, by means ofthermal analysis, solidification microstructure, X-ray diffraction, energy spectrumanalysis and thermoelectric property measurement, we studied the effect of melt heattreatment on solidification behaviors, resulted structures and thermoelectric property of(BiXSb1-X)2Te3. The main innovative conclusions are summarized as follows:1. The obvious abnormal behaviors appeared on the electrical resistivity vstemperature (ρ-T) curves of molten p-type thermoelectric alloys (BiXSb1-X)2Te3(X=0.3,0.4,0.5) at the heating processes, while the curves became smooth in the followingcooling, which suggest the irreversible temperature-induced melt structure transitionoccurred in the liquid alloys.2. Solidfication thermal analysis and microstructure test indicated that there weretwo phases in the solidified structures of the (BiXSb1-X)2Te3(X=0.3,0.4,0.5) alloys. Forthe melts experienced the melt structure transition, the nucleation and growthundercooling degrees enlarged, the latent heat release rate during the nucleation stageincreased，the strips of intermetallic phase refined and its preferential orientationweakened, the amount of Te based solid solution increased.3. The Seebeck coefficient and electrical resistivity measurements demonstrated thatmelt structure transition had remarkable influences on thermoelectric property. For theBi0.3Sb1.7Te3, Bi0.5Sb1.5Te3alloys experienced the nelt structure transition, the Seebeck coefficient enlarged dramatically and the electrical resistivity reduced, thusthe highest power factor reached8.66×10-3W/(mK2) and6.28×10-3W/(mK2), whichpromoted142%and107%respectively.From above conclusions, the melt status transition in Bi-Te basedthermoelectric material can obviously affected the solidification structure,therefore significantly improved the thermoelectric property. Thus it is of greatsignificance to control the melt status to improve the thermoelectric propertyby utilizing melt treatment.