Temperature Dependence Of Electronic Transport Properties In Sn-(Bi, Pb, In) Melts And The Correlation With Solidification

As well known,the knowledge on liquid structures and properties is closely related to the scientific and technical advance in material processing,liquird physics and other fields.In recent years,the phenomena of liquid polyamorphism bring great interest to relevant realms. More and more evidences suggest that pressure or temperature induced liquid-liquid structure transitions(TI-LLST)could occur in liquids.All these present challenges to our conventional picture of liquid as entity with a continuously varying averaged structure,and provide new breakthrough to further recognize liquid substances.As a new field,the up-to-now studies of liquid polyamorphism have been focused on phenomenology.There are still more works need to be done about the essence and mechanism of liquid polyamorphism,the electronic level of liquid structure transitions etc. Therefore,in this paper,the temperature dependence of electrical resistivity(p-T), thermoelectric power(S-T)and the X-ray diffraction of liquid Pb-Sn,In-Sn,and Sn-Bi alloys were investigated,and the characteristic,mechanism and essence of TI-LLST were studied and discussed with the help of some theories,such as Fiber-Ziman theory and Mott shift.In addition,the effects of liquid-liquid structure transition on the solidification of SnBi alloys were studied also.The major contents and conclusions are as follows.Firstly,the author refitted the experimental equipment and maked it possible to investigate simultaneously the conductivity and the thermoelectric power of liquid alloys. The good agreement of the experimental results with other resorts lets us to believe that it is a valid research method for studying the liquid structures.Secondly,for the first time,the conductivity and the thermoelectric power of liquid InSn,PbSn and SnBi alloys were studied simultaneously.Anomalous phenomena were found to occur with temperature hundreds of degrees above the liquidus,which suggested that the temperature induced liquid-liquid structure transition(TI-LLST)occurred in these alloys.Furthermore,the liquid structure transitions of Pb_(100-x)Sn_x(x=40,61.9,80)are reversible.Thirdly,based on the experimental results,by means of Faber-Ziman theory,the temperature dependence of the density of electronic states N(E_F)and its gradient value dN(E_F)/dE were deduced.The results indicated that the variations of the electronic structures occurred during liquid structure transitions.These contents and results had never been reported before.Fourthly,from the viewpoint of melt structure transition,the solidification behaviors and morphologies of Sn-Bi alloys under different melt overheating treatments were studied.The results showed that melt superheating treatments could refine the solidified structures.The reason is that the melt experienced structure transition becomes more homogeneous and disorder and needs higher degree of supercooling during solidification;besides,with the Bi contents increasing in Sn matrix,the solidified microstructure under the same thermal history becomes finerThe new phenomena,results and regulations reflected in this paper could enrich our knowledge on the mechanism of liquid structure transitions further to reach to the electronic level,provide a new basis for deeper understanding the essence of liquid structure transitions,and are also of significance for promoting the innovation of material processing.