Xian-Fen Li

Electrical resistivity of liquid Sn–Sb alloy

An investigation of the temperature dependence of the electrical resistivity (ρ–T) of Sn–Sb alloys is carried out, using the DC four-probe method. A clear turning point is observed in some compositions of the Sn–Sb melt, but not at every composition, at which the resistivity–temperature coefficient increases rapidly. The anomalous variation of the resistivity at certain temperatures for the Sn–Sb melt may be due to the remaining covalent and heterogeneous bonds and also the difference in bonding ability between Sn and Sb atoms, which might yield temperature-induced structure changes in some compositions of liquid Sn–Sb alloys. Besides this, analysis of the composition dependence of the resistivity is also included in this paper.

Hump phenomenon on resistivity–temperature curve in liquid Bi, Sb and their alloys

The electrical resistivities of liquid Bi, Sb, and some of their alloys Pb–Bi, Pb–Sb have been investigated as a function of temperature, and the effect of heating-rate on the turning points of liquid Bi has also been investigated. Obvious and interesting hump phenomena are observed on resistivity–temperature curves of liquid Bi, Sb, and Pb–Bi, Pb–Sb alloys on heating at the temperature far above their liquidus. Moreover, the transition temperature of liquid Bi increases with heating-rate increasing, which shows that this kind of transition is in accordance with kinetic characteristics. However, comparing the heating curve with the cooling one, we found that the anomalous hump phenomenon is irreversible in liquid Bi, Sb, and Pb–Bi, Pb–Sb alloys.

Electrical resistivity of liquid Bi–Sb alloys

The electrical resistivities of liquid Bi–Sb alloys have been measured by DC four-probe method within Bi-rich composition through a wide temperature range. The distinct anomaly of a hump shape was observed on resistivity–temperature (ρndash;T) curves for liquid Bi–Sb alloys on heating at the relatively high temperatures. These anomalies have revealed the temperature-induced liquid–liquid phase transition in Bi–Sb melts. The DSC results for BiSb20wt% alloy further prove the existence of liquid–liquid transition. Measuring the ρ–T curves first on heating and then on cooling we have found that on cooling the ρ–T curve remained linear. It means that the postulated liquid–liquid transition may be irreversible.

Study on temperature dependence of resistivity in liquid In–Sn alloy

The electrical resistivity of liquid In–Sn alloy was measured by a dc four-probe method. In a relatively low-temperature zone above liquidus, resistivity changes discontinuously; only the changing trend is altered, whereas resistivity changes sharply in the high-temperature zone and the changing pattern is completely different from the ones at low temperature. The unusual change of resistivity reflects the alteration of the mean free path L0 of conduction electrons and also the electron transport properties. Consequently, we assume that structural changes might occur in the continuous heating process. Transition temperatures are different for In–Sn melts with various compositions. The resistivity behaviour of eutectic composition is distinguished from others and its transition temperature is the lowest.

THE ELECTRICAL RESISTIVITY OF LIQUID Pb-Bi ALLOY

Different from the conventional liquid theory, experimental evidence suggests that there might be discontinuous liquid-liquid (L-L) structure transitions for some alloys. By the resistivity experiments, it is assumed that a temperature-induced L-L structure transition might occur in liquid lead-bismuth (PbBi) alloy. The electrical resistivity of four compositions for PbBi alloy versus temperature was precisely measured in our experiment. It was found that the resistivity increases linearly with temperature rising in a certain range of temperature above the melting point. During subsequent calefaction, the results obviously showed that a turning point appears in the resistivity-temperature (R-T) curve for every composition at a certain temperature. The turning temperature depends on composition. It can be considered that there is L-L structure transition in some regions of high temperature for PbBi alloy.

Effect of liquid–liquid transition on solidification of Bi–Sb10 wt% alloy

In our previous study, the electrical resistivities of liquid Bi–Sb alloys were measured by DC 4-probe method in a wide temperature range. Their anomalous change with temperature indicated the existence of temperature-induced liquid–liquid transition (LLT) in liquid Bi–Sb alloys. Based on the results of LLT, corresponding solidification experiments have been carried out on the Bi-Sb10 alloy, i.e., the Bi–Sb10 alloys are melted and held at the temperature above and below the LLT respectively, and then cooled from the same temperature. The results of solidifying experiments show that LLT has a significant effect on the solidification behavior and microstructure. The general rule is that the under-cooling degree increases, the solidification microstructure becomes finer, and the obvious change of microstructure morphologies takes place when solidifying from the liquid-experienced LLT.

Temperature-induced liquid–liquid transition process in eutectic Pb–Sn melt explored from kinetic viewpoint

Up to now, there have been few studies of the temperature-induced liquid?liquid structure transition (LLST) kinetics for atomic systems. In this paper, through isothermal and heating experiments, we have investigated the kinetics of the LLST process in Pb?Sn61.9?wt% melt by measuring the electrical resistivity and heat flux. The time evolution of the heat flux and electrical resistivity can be described by the Johnson?Mehl?Avrami model with an Avrami exponent of 3.87, which is an indication of nucleation-growth-type ordering of the nonconserved order parameter. What is more, we have calculated the reaction rate constant KT and apparent activation energy ?E, and deduced the reason for the characteristics of temperature-induced LLST. The result of this research could be beneficial for a further understanding of the essence of LLST.

The abnormal changes of electrical resistivity in liquid Pb–In alloys

Electrical resistivity of liquid lead and indium (Pb–In) alloys with different compositions has been measured using the four-probe method in a large temperature range. Marked turning points on each resistivity–temperature (ρ–T) curve of the liquid Pb–In alloys can be observed far above the liquidus. The unusual variation of the resistivity of Pb–In melts suggests a structural transition of these melts, for resistivity is a sensitive parameter to the structure. Moreover, the DSC experiment of Pb–In melts supports the existence of a liquid–liquid (L–L) structure transition in Pb–In melts. Such a L–L structural transition can be described in terms of the gradual disappearance of atomic bonds corresponding to the crystal structure and/or to a reduction of the size of pre-formed atomic clusters. This implies an increase of disorder in the high temperature melts. The transition temperatures depend on the composition of Pb–In melts and the onset transition temperatures of the intermediate phase (α) Pb–63%In and Pb–70.6%In melts are higher than that of other compositions.

Reversible resistivity–temperature anomalies of liquid Pb–Bi–Sn alloys

The patterns of electrical resistivity of (Pb–Bi56.1)1− x –Sn x alloys, along with liquid Pb–Bi56.1 wt% alloy and pure Pb, Sn and Bi have been investigated as a function of temperature, using the DC four-probe technique. Evident reversible changes are observed on resistivity–temperature curves of different liquid Pb–Bi–Sn alloys, and there are clear turning points both in the heating and cooling process, which are similar to that of liquid Sn. Moreover, the turning temperatures vary with differing compositions of alloys. In the case of the Pb–Bi alloy, however, no reversible changes are observed on resistivity–temperature curves. Since resistivity is one of the physical properties sensitive to structures, it is suggested that there are reversible temperature-induced liquid–liquid transitions in (Pb–Bi56.1)1− x –Sn x alloys, and that Sn plays an important role in the change.

Effects of compound formation on liquid structure in Cu–Sn melts as a function of temperature

Through the theoretical study of concentration-dependent thermodynamic and microscopic functions in some reports, chemical short-range orders (CSROs) have been proved to persist in Cu–Sn melts. However, it is not clear insofar in which concentration and temperature ranges do these CSROs exist in melts, and how they change with temperature. This study investigates the liquid structure with temperature of Cu–Sn alloys by electrical resistivity and DSC. The results show that some CSROs inheriting solid structures bring abnormal transition of resistivity at a temperature hundreds of degrees above the liquidus for all the studied Cu–Sn melt. Especially for the melts with 50 to 70% Cu, there also exist ‘associates’ of unlike atoms, which reduce continuously with increasing temperature after melting and result in negative temperature coefficients of resistivities (TCRs). In the figures of DSC-temperature, some endothermic peaks consistent with the temperatures of resistivity transitions verify these abnormal transitions of liquid structure.