Surface-directed and bulk spinodal decomposition compete to decide the morphology of bimetallic nanoparticles

Pankaj, P and Bhattacharyya, S and Chatterjee, Subhradeep (2022) Surface-directed and bulk spinodal decomposition compete to decide the morphology of bimetallic nanoparticles. Modelling and Simulation in Materials Science and Engineering, 31 (015003). pp. 1-10. ISSN 0965-0393

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Abstract

An embedded-domain phase-field formalism is used for studying phase transformation pathways in bimetallic nanoparticles (BNPs). Competition of bulk and surface-directed spinodal decomposition processes and their interplay with capillarity are identified as the main determinants of BNP morphology. Two dimensionless groups are found to reflect this competition and interaction: (a) the ratio of bulk to capillary driving forces ( Δ f ˜ ), and (b) ratio of difference in surface energies to the interfacial energy which relates to the three-phase contact angle (θ). The simulated morphologies, namely, core-shell, Janus and inverse core-shell, are found to cluster neatly into distinct regions of the Δ f ˜ -θ space. To connect phase-field simulations with specific BNP systems, the variation of θ with Δ f ˜ as a function of temperature is computed for Ag-Cu using a CALPHAD approach. The computed Δ f ˜ -θ trajectory for Ag-Cu, when superimposed on the morphology map derived from simulations, enabled the prediction of different morphological transitions as a function of temperature. Therefore, by providing an alternative and efficient approach to connect phase-field simulations with CALPAHD, the study demonstrates a unique computational framework that can assist in tailoring nanoparticle morphology through a variation of processing parameters. © 2022 IOP Publishing Ltd.

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