The nature of liquid structures with their changing behaviors remains an unsolved fundamental problem in many fields of science and technology. It has been widely accepted that liquid structures change gradually with temperature and/or pressure. With x-ray diffraction in the melt In-Sn80, however, we have confirmed that a temperature-dependent discontinuous structural change could occur in some binary liquids, which does not fall into any other up-to-date recognized liquid-liquid changes. This finding, together with the recently recognized pressure-induced liquid change, suggests that the conventional view on liquids should be revised.

A first-order liquid-liquid (LL) phase transition as a function of temperature in Pb-Sn melts is suggested by internal friction experiments and verified by differential thermal analysis with an entropy-driven order-disorder mechanism. It differs remarkably with other already found LL phase transitions in some aspects. The findings may throw light on the nature of viscous liquids in condensed state physics and be of significance in materials science. The present work makes a beneficial attempt at exploring internal friction as an experimental method for studying liquids.

With the help of an improved internal friction method, it was found that a peak could appear, as the temperature increased, above the liquidus in each of the internal friction curves of Pb-Bi alloys. The features of this kind of peak are similar to those found during the solid-liquid transition in the same experiments, and in accordance with the characteristics from solid-solid transitions verified by previous investigators. The results suggest that structural changes take place to some extent in the molten alloys as a function of temperature, which have been confirmed by the corresponding calorific peak in a differential scanning calorimeter. This phenomenon might help in understanding the nature of molten alloys and their melting mechanism as well. In addition, the internal friction technique proved to be quite sensitive to liquid structures and effective for studying liquid materials.