Structural Evolution In Sn-Zn Metallic Liquids

The structure characteristics of metallic liquids have important influence on the structural evolution of materials in the process of solidification,and their following properties.Thus,in recent years,the structural evolution of metallic liquids has gradually become one of hot issues in both condensed matter physics and materials science.The metallic liquids are usually regarded as identical and homogeneous phase,however,many reports confirm that the liquid-liquid transition(LLT)could happen in several metallic liquids by changing external temperature and pressure,accompanied with the changes in electrical resistance,thermoelectric properties,etc,simultaneously.Whether the development of new structural materials or functional materials,it is indispensable to know the structure of such kinds of materials.Therefore,studies on the detailed structural evolution of metallic liquid are of great significance to scientific research and industrial applications.This thesis mainly focuses on Sn-Zn metallic liquids and has following main contents:(1)Temperature-dependent atomistic structural evolution in liquid Sn85Zn15 eutectic alloy is investigated by using in situ high energy X-ray diffraction and ab initio molecular dynamics simulations.We reveal a structural crossover at around 900 K in liquid Sn85Zn15 eutectic alloy,below and above which the liquids exhibit different changes in first peak position shifts on S(q)and G(r)curves,the nearest coordination number and activation energies for self-diffusion.This structural crossover is likely ascribed to the spatial connectivity variation of local clusters.(2)The structure of liquid Sn and Zn in the process of heating and cooling is also studied.Upon heating,a contraction instead of an expansion for the first coordination shell in liquid Sn and Zn is revealed.In the high temperature region,the clusters with smaller coordination number are more likely to exist in liquid Sn and Zn.And the liquid-liquid transition is also observed in liquid Sn,which is not found in liquid Zn but also not the same to that in the liquid Sn85Zn15 eutectic alloy in the whole temperature region.