Atomistic Imaging of Competition between Surface Diffusion and Phase Transition during the Intermetallic Formation of Faceted Particles

Abstract

To explore the ordering mechanism of facet alloy nanocrystals with randomly distributed atoms, we investigate kinetic and thermodynamic behaviors of the ordering phase transition from face-centered cubic Pt3Co nanocrystals to L12-Pt3Co intermetallic nanocrystals. It is observed that the ordering occurs from the surface and then gradually into the interior in a layer-by-layer mode, involving the competition between two kinds of phase transition modes: long-range surface diffusion-induced phase transition (SDIPT) and short-range reconstruction-induced body phase transition (RIBPT). The density functional theory calculations demonstrate that the surface status acts as a pivotal part in the thermodynamics and kinetics of the nanoscale ordering transition. With the development of the controllable heating process, both SDIPT and RIBPT modes can be manipulated as well as the morphology of the final product. This in situ work lays the foundations for potentially realizing shape-controlled intermetallic nanostructures by utilizing the thermal annealing method and makes preparations for the rational design of the surface and near-surface atomic configurations at the atomic scale.

Engineering the degree of concavity of one-dimensional Au–Cu alloy nanorods with partial intermetallic compounds by facile wet chemical synthesis

“…38 For instance, the phase transition of cubic Pt 3 Co nanocrystals from a solid solution to an intermetallic phase via high temperature annealing was investigated using in situ scanning transmission electron microscopy. 39 The results showed that two mechanisms of phase transition exist, resulting in a layer by layer ordering of atomic arrangements from the surface to interior. One is the long-range surface-diffusion-induced phase transition, which begins at relatively low temperature and could induce phase transition at the initial time at a temperature setting of 600 °C.…”

Kinetic diffusion–controlled synthesis of twinned intermetallic nanocrystals for CO-resistant catalysis

“…The interfaces generated from these defects commonly promote the catalytic activity by regulating the specific adsorption, desorption, and activation of molecules (39)(40)(41)(42)(43). To date, synthesis of intermetallic nanocrystals with controlled interface structure remains challenging, partially because of the complex growth and ordering processes (44)(45)(46)(47)(48)(49)(50). Regardless of the alluring performance, it is essential to elucidate the microscopic origin mechanisms of interface in intermetallic nanocrystals and its structure-function relationship.…”

Singular behaviour of atomic ordering in Pt–Co nanocubes starting from core–shell configurations

“…Although the surface-influenced ordering seems useful to control the Pt-Co nanoparticle structure, such ordering has not been observed. 5,19,20 Researchers have conducted annealing experiments of solid-solution particles. In those experiments, the particles had the ordered structure that can be expected from the total composition ratio and bulk phase diagram.…”