Thermodynamics of CuPt nanoalloys

• Published in: Scientific reports Vol. 8; no. 1; pp. 9150 - 9
• Main Authors: Rossi, K., Pártay, L. B., Csányi, G., Baletto, F.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 14-06-2018; Nature Publishing Group
• Subjects: 119/118; 639/301/357/354; 639/925/357/354; Approximation; Humanities and Social Sciences; Investigations; multidisciplinary; Nanoparticles; Science; Science (multidisciplinary); Simulation; Solidification; Solids; Thermodynamics
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-27308-1

The control of structural and chemical transitions in bimetallic nanoalloys at finite temperatures is one of the challenges for their use in advanced applications. Comparing Nested Sampling and Molecular Dynamics simulations, we investigate the phase changes of CuPt nanoalloys with the aim to elucidate the role of kinetic effects during their solidification and melting processes. We find that the quasi-thermodynamic limit for the nucleation of (CuPt)
309
is 965 ± 10 K, but its prediction is increasingly underestimated when the system is cooled faster than 10
9
 K/s. The solidified nanoparticles, classified following a novel tool based on Steinhardt parameters and the relative orientation of characteristic atomic environments, are then heated back to their liquid phase. We demonstrate the kinetic origin of the hysteresis in the caloric curve as (i) it closes for rates slower than 10
8
 K/s, with a phase change temperature of 970 K ± 25 K, in very good agreement with its quasi-thermodynamic limit; (ii) the process happens simultaneously in the inner and outer layers; (iii) an onion-shell chemical order - Cu-rich surface, Pt-rich sub-surface, and mixed core - is always preserved.