液体-液体相变与反常特性

绝大多数物质的液态密度随温度降低而增大,即常见的热胀冷缩现象.但存在一类物质,如水及第四主族的硅、锗等,其液态密度在一定温度范围内随温度的升高而增大,即密度反常现象.此外,该类物质还存在动力学反常(密度越大粒子运动越快)、热力学反常(热力学量的涨落随温度降低而升高)等其他反常特性.这类材料的化学性质千差万别,但却具有相似的物理反常特性.进一步的理论研究发现部分材料具有两种液态,即高密度液态和低密度液态,两者之间存在一级相变.因此,反常特性与液体-液体相变是否有直接关联是一个值得深入研究的课题.本文主要介绍了具有液体-液体相变的一类材料及其反常特性,包括高温高压下氢的液体-液体相变及其超临界现象,镓的反常特性及其与液体-液体相变的关联等.

Liquid-liquid phase transition and anomalous properties

In most of liquids, densities increase as temperature decreases. However, the densities of water and water-like liquids, such as silicon and germanium, are anomalous, which increase as temperature increases. Such substances also show other anomalous behaviors, such as diffusivity anomalies (diffusivities increase as density increases), and thermodynamic anomalies (the fluctuations increase as temperature decreases). The chemical properties of these materials are very different from each other, but they all share similar physical properties. Further studies indicate that most of them have two distinct liquid states, i.e., a low-density liquid and a high-density liquid, and a first order liquid-liquid phase transition (LLPT) between these two liquids. We mainly discuss the anomalous properties of materials each of which has a predicted LLPT and their relations with anomalous behaviors (thermodynamic, dynamic and structural) as those of water and water-like liquids, such as hydrogen and gallium. In particular, we discuss the supercritical phenomenon of the liquid-liquid phase transition of hydrogen, as well as the liquid-liquid phase transition of gallium and its relation with the thermodynamic, dynamic, and structural anomalies. It is found that the liquid hydrogen and gallium both have the LLPT and share similar anomalous behaviors as water and water-like liquids, such as density anomaly, dynamics anomaly, thermodynamic anomaly Since the chemical properties of these materials are very different from those of others having the LLPT, the anomalous behaviors may be common features for substances predicted to have the LLPT.