Simulation of Size Effects upon Phase Transformations in Submicrometer Particles of an Au–Pt–Pd Alloy

Size effects are observed in phase equilibria in micro- and nanoparticles. They are mapped in the phase diagrams as shifts of characteristic lines and points. Here, these effects are simulated and mapped for ternary systems. The influence of the alloy composition on the region of existence of core–shell states is simulated for Au–Pt–Pd solid solution particles 250 nm in radius by the chemical thermodynamic methods. It is shown that the region of layering of this solution decreases and is separated due to the competition of the core–shell states with the segregation of Pt in the core or in the shell phases. The conoids of stable and metastable equilibrium core–shell states are built in the phase diagram. The characteristics of these states (the composition of existing solutions and the core phase radius) are presented. The regularities described in this report are topical when considering the catalytic activity of Au–Pt–Pd alloy particles.