Structural Transformations in Bimetallic Ni–Ag Nanoparticles with Janus Structure

Structural transformations in Ni–Ag bimetallic nanoparticles sized 5 nm were investigated after a cycle of sequential phase transitions corresponding to melting and crystallization. The initial configuration of the Ni–Ag bimetallic nanoparticles corresponded to a Janus structure. Two alternative methods — molecular dynamics and Monte Carlo methods — were used to simulate the thermally induced effects. The tight binding potential was used as the intermolecular interaction potential. It was shown that for Ni–Ag bimetallic nanoparticles, surface segregation of Ag atoms is characteristic, and specific features of the segregation behavior of Ag atoms at different concentrations were identified. The obtained regularities are compared with the experimental results for Ni–9 wt. % Ag nanoparticles synthesized by the method of electric explosion of wires, which is characterized by the formation of particles with a "core–shell" structure. Based on the analysis of calorimetric curves of the potential part of the specific internal energy, hysteresis of the melting and crystallization temperatures was revealed, allowing for the estimation of the starting and finishing temperatures of the corresponding phase transition, as well as determining the thermal stability intervals. In addition, it was found that with an increase in the number of nickel atoms in the composition of the particles, the width of the hysteresis of the melting and crystallization temperatures increases.