A universal signature in the melting of metallic nanoparticles

TL;DR

This paper identifies a universal structural signature in the pair distribution function that signals the melting of metallic nanoparticles across different elements and sizes, providing a measurable and reliable indicator.

Contribution

It introduces a universal, experimentally accessible signature based on the pair distribution function to detect nanoparticle melting, applicable across various metals and configurations.

Findings

Disappearance of the second nearest neighbor peak signals melting.

The relative cross-entropy correlates with caloric curves and indicates a quasi-first order transition.

Method effectively identifies melting temperatures even in complex environments.

Abstract

Characterizing the melting behaviour of monometallic nanoparticles is a great challenge from both the experimental and the theoretical point of view. To this end, we disclose a universal signature based on the cluster's pair distribution function, a measurable quantity from X-ray experimental analysis tools. From a systematic investigation of metallic nanoparticles of different chemical species (Ni, Cu, Pd, Ag, Au and Pt), in a wide size range (146 to 976 atoms), and using both crystalline and five-fold twinned shapes as initial configurations, it emerges that the melting transition is signalled by the disappearance of a peak at the second nearest neighbours in the pair distribution function. To this end, we show that the relative cross-entropy of the pair distribution function between a "cold" and a "hot" reference structure correlates with their caloric curves, thus also presenting a quasi-first order transition at the melting temperature. Finally, we demonstrate the fruitful application of the proposed structural characterization method to identify the melting temperature of nanoparticles in a strongly interacting environment, where low-symmetry solid and melted phases are quasi-degenerate in energy.