Phase stability of Ag–Sn alloy nanoparticles

• The phase diagram of Ag–Sn nanoparticles (NPs) is presented.
• The calculated phase diagram agrees well with the experimental data.
• The eutectic temperature decreases as the particle size decreases.
• The eutectic composition moves to the Sn-rich side as the particle size decreases.

Nanoparticles often possess phase stabilities that differ from those of bulk materials, as a result of their large surface-to-volume ratio. Park and Lee suggested that the phase diagram of metallic nanoparticles can be calculated using the CALPHAD method through the introduction of the size effect. Based on Park and Lee’s model, the thermodynamic parameters for the Ag–Sn nanoparticle system (pure Ag and Sn, the intermetallic compound Ag3Sn, and liquid and solid solutions (fcc, hcp, and bct)) were optimized as a function of temperature, composition, and the size of the nanoparticle. The phase stability of the Ag3Sn nanoparticles was affected by the selection of the surface tension value for Ag3Sn; however, the eutectic temperature and composition are not affected by the phase stability of the Ag3Sn nanoparticles. When the size of the nanoparticles is decreased, the eutectic temperature decreases, and the eutectic composition approaches the Sn-rich corner. The present results exhibited a reasonable agreement with the reported experimental data.