Continuous melting and thermal-history-dependent freezing in the confined Na-K eutectic alloy

TL;DR

This study uses 23Na NMR to reveal that melting and freezing in confined Na-K eutectic alloy are continuous and depend on thermal history, challenging existing theories of phase transitions in nanoscale confinement.

Contribution

The paper demonstrates that melting and freezing in confined Na-K alloys are continuous processes influenced by thermal history, prompting a revision of theoretical models.

Findings

Melting of Na2K nanoparticles is a continuous process.

An intermediate stable state exists during melting.

Freezing can be sharp or continuous depending on initial cooling temperature.

Abstract

23Na NMR studies of the Na-K eutectic alloy embedded into porous glass with 7 nm pores showed that melting of Na2K confined nanoparticles is a continuous process with smooth changes in the Knight shift of a narrow resonance line and nuclear spin relaxation between those in the crystalline and liquid states. The intermediate state which occurs upon melting is stable and more favorable than the liquid state. The inverse freezing transformation can be sharp as at a first order transition or continuous depending on the initial temperature of cooling. The results suggest revision of theoretical predictions for the melting and freezing transitions in confined geometry.