Local order and thermodynamics of low-melting Gallium alloys

Liquids are omnipresent in our daily lives and are at the basis for many processes in biology, industry and the production of goods. One group of liquids are the melts of metallic elements and their mixtures, also known as liquid alloys. We often think of liquids as uniform and without internal structure, but it was found that the atoms or molecules in many liquids can show unexpected, non-random arrangements at the nanometer scale. In this behavior they disobey traditional conceptions of the mechanism of the liquid-to-solid freezing transition. Liquid alloys containing the element gallium can show freezing points below room-temperature while remaining liquid up to 1500 C. They are attractive as alternative heat-transfer medium in power plants, as batteries electrodes, in microfluidics and other emergent applications. It is hardly investigated how the atoms in these liquid alloys interact, which is key to an understanding of their properties and for the development of next- generation liquid alloys with superior properties. In this project I will investigate how atoms in liquid gallium alloys interact, which local order can be found on the atomic scale and how one can relate this order to their macroscopic properties. Three systems with increasing complexity, the gallium-indium, the gallium-iodine and the gallium-indium-tin system will be investigated using X-ray and neutron diffraction techniques. The obtained data will be analyzed with state-of-the-art computational structure analysis algorithms like the Empirical Potential Structure Refinement method or reverse- Monte-Carlo approaches. Measurements of vapor pressure, viscosity and thermal behavior will complement the characterization. After gaining a deeper understanding of these three systems, a model will be built based on published data to generalize the relation between atomic scale and macroscopic properties, with the potential of property prediction and more streamlined alloy development for novel applications. For this work I will join the group of Prof. Christoph Salzmann at the University College London, who is a leading expert in the structure analysis and modeling of liquids and disordered materials. I will complement his expertise with my knowledge on the chemistry and physics of metals and intermetallic compounds. In the return phase at the University of Vienna, my newly acquired knowledge will enrich the pools of methods in the group of Prof. Hans Flandorfer and pave the way to strengthen the development of this future research branch in Austria.

In this project, the short-range order in liquid Ga-In alloys was investigated. In the binary Ga-In system, an atomistic structure model was established by a combination of x-ray and neutron diffraction. The results indicate that there are no preferred interactions between atomic species in this liquid alloy system and that the short range order is dominated by size mismatch. This contradicts theoretical studies which predict a charge transfer between Ga and In. In the Gallium-iodine system, a new glass with composition Ga2I3.17 was discovered which displays high ionic conductivity. Furthermore, several liquid molten salts have been investigated and properties of the halogen bond have been characterized.