Phase-Field Modeling of Phase Transformations in Platinum-Based Alloy Nanoparticles

Abstract

A phase-field model that describes the phase decomposition and phase transformations inside platinum-based alloy nanoparticles is developed to elucidate the effects of particle size, alloy composition, and heat-treatment temperature on the microstructure formation. FePt, CoPt, NiPt, CuPt and IrPt binary alloy nanoparticles with diameters of less than 10 nm are investigated. The calculation results clearly show that surface segregation and atomic ordering are sensitive to the alloy components and particle size, and that the equilibrium nanostructure obtained varies according to the balance between the surface energy and chemical interaction between atomic components. Platinum-based alloy nanoparticles are expected to find applications as electrocatalysts in polymer electrolyte fuel cells. Thus, the proposed phase-field approach demonstrates its usefulness for the control of the radial distributions of each alloying component within a nanoparticle, leading to improvements in the activity and durability of the catalyst and reducing the required amount of platinum loading.

Nanostructure-induced L10-ordering of twinned single-crystals in CoPt ferromagnetic nanowires

“…The ordering mechanism in nanostructured CoPt and FePt has been studied theoretically and experimentally in terms of free surface, surface segregation, surface diffusion, defect, size, and shape. 107–128 For example, L 1 0 -ordering has been found to proceed more quickly at the free surfaces than at the core of the nanostructures. 120,124 Surface segregation of Pt has been found to regulate the stoichiometry of the inner layers below the top surface, leading to affect the atomic ordering of the core of the nanostructures.…”

Development of hybrid model for modeling of diffusion phase transformation

“…Modeling of phase transformations is just beginning to be widely used, and because of the diversity and complexity of this type of process, only very limited variations of the transformations and conditions of their occurrence are considered. Main tools for modeling of phase transformations are CA (An et al , 2014; Halder et al , 2014), finite difference method (Singh, 2015; Wang et al , 2013) and phase field method (Malik et al , 2013; Yamakawa et al , 2013; Zhao et al , 2017; Zhu et al , 2015). Nowadays, existing models consider only separate parameters of processes or their separate stages.…”