Crystallization and short-range order of high-entropy materials (HEMs) by molecular dynamics (MD) simulations. (T)

ΕΠΙΒΛΕΠΩΝ : ΕΙΡΗΝΗ ΓΟΥΔΕΛΗ, Αναπλ. Καθ. Χημ. Μηχ. Παν/μιο Πατρών (πληροφορίες: eirini.goudeli@unimelb.edu.au)

Non-equilibrium nanomaterials are rapidly emerging owing to their unparalleled catalytic, electrochemical and sensing properties. By accessing compositions and crystal phases unattainable under equilibrium conditions, they can unlock potential for advanced materials in catalysis, healthcare, and energy applications, outperforming conventional equilibrium materials. These otherwise unattainable non-equilibrium nanostructures can be captured in flame synthesis methods those by kinetically “trapping” them upon rapid heating-cooling. Little is known, however, about the role of operating conditions and reactor design on crystal phase formation and compositional homogeneity. 

This project atomistic-level simulations would be used to explore how multi-metallic high entropy materials (HEMs) with well-controlled nanostructured characteristics form in flames. Amorphous multicomponent nanoparticles would be generated upon extreme heating to mimic nanoparticle formation at the high temperature region of the flame. A Fe/Co/Ni/Mo/Cu composition would be used as a model HEM, upon validation of available interatomic potentials [1]. 

The crystallization of these nanoparticles would be simulated by molecular dynamics (MD) simulations upon cooling at different target temperatures. The effect of temperature history on the kinetic trapping of high entropy alloys would be explored by XRD calculations of the MD-obtained atomic trajectories, Steinhardt parameters [2], and disorder variable [3] analysis to quantify the local crystalline structure. Distinct crystallization pathways that may occur depending on the cooling rate will be investigated, as demonstrated by such simulations for Au (Fig. 1) [4].

The role of process conditions on atomic mixing would also be explored, identifying conditions that lead to good atomic-scale mixing versus segregation, for a range of atomic compositions. The short-range order and potential non-random local bonding would be described by radial distribution function calculations and bond length distribution analysis. These metrics would be also used to determine metal-oxygen bond lengths within high-entropy oxide nanoparticles, aiming to reveal the mechanism by which oxygen vacancies affect the nanostructure. This project will contribute to the rational design of truly new non-equilibrium nanostructured materials by advancing the knowledge base of their formation by a proven scalable synthesis technology. A systematic investigation of process conditions affecting structural, compositional, and physical properties of HEMs will establish structure-property relationships, essential for process scale-up and industrial exploitation.