Regensburg 2025 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 12: Materials for the Storage and Conversion of Energy

MM 12.9: Talk

Tuesday, March 18, 2025, 12:30–12:45, H22

Extracting Gibbs free energies from local composition fluctuations in atom probe data — •Parisha Diwan, Jianshu Zheng, Rüya Duran, Guido Schmitz, and Sebastian M. Eich — University of Sttugart

In this work, thermodynamic fluctuation theory which is traditionally used for liquids has been extended to solids by incorporating an additional elastic work component to account for local composition variations, which is not present in liquids. In solids, composition fluctuations are quantified through the relative variance of the composition histogram, which is influenced by the evaluation volume size and interface effects. These fluctuations are key to determining the Gibbs free energy of mixing in solid alloys. The technique most suitable for identifying local composition fluctuations is Atom Probe Tomography (APT), which provides high-resolution, 3D spatial chemical information at the atomic level. This allows for the detection of local composition variations in solid materials, making it an ideal tool for the evaluation of the extended fluctuation theory. The study applies this theory to a Cu-Ni alloy, using experimental APT data and spatial frequency distribution analysis. By comparing the results with existing phase diagram data, the method demonstrates its effectiveness in extracting the Gibbs free energy of mixing from local composition fluctuations in solids. The comparison with the latest CALPHAD depiction of the miscibility gap further supports the reliability of the method, showing that the proposed approach can accurately predict thermodynamic properties in solid alloys based on atomic-scale data.

Keywords: Thermodynamics; Fluctuation theory; Copper Nickel Alloy; Atom Probe Tomography; Phase Diagram