Two-step melting of Na41+

TL;DR

This study measures the heat capacity of Na41+ clusters, revealing a two-peak structure indicating melting and premelting phenomena, contrasting previous findings of a smooth transition due to improved measurement accuracy.

Contribution

The paper introduces a differential nanocalorimetry method that uncovers detailed heat capacity features of Na41+ clusters, demonstrating a two-step melting process.

Findings

Identification of a two-peak heat capacity structure in Na41+

Evidence for melting and premelting transitions in Na41+

Observation of an anti-Mackay to Mackay solid-solid transition

Abstract

The heat capacity of the mass selected Na41+ cluster has been measured using a differential nanocalorimetry method. A two-peak structure appears in the heat capacity curve of Na41+, whereas Schmidt and co-workers [ M. Schmidt, J. Donges, Th. Hippler, and H. Haberland, Phys. Rev. Lett. 90, 103401 (2003) ] observed, within their experimental accuracy, a smooth caloric curve. They concluded from the absence of any structure that there is a second order melting transition in Na41+ with no particular feature such as premelting. The observed difference with the latter results is attributed to the better accuracy of our method owing to its differential character. The two structures in the heat capacity are ascribed to melting and premelting of Na41+. The peak at lower temperature is likely due to an anti-Mackay to Mackay solid-solid transition.