Pressure-induced superheating of Al nanoparticles encapsulated in Al2O3 shells without epitaxial interface

Quantitative measurements were carried out on the pressure effect of superheating of Al nanoparticles encapsulated in Al2O3 shells without epitaxial interfaces. In situ XRD experiments revealed that encapsulated Al nanoparticles with different particle sizes can be superheated to 7-15 K beyond the bulk equilibrium melting point of Al, and that this is accompanied by a suppressed thermal expansion behavior. A value for the pressure build-up on the Al core due to the constraint of the rigid Al2O3 shell of up to 0.25 GPa was derived from the temperature dependence of the lattice spacing for the superheated samples. The correlation between the measured pressure and superheating verified that the observed superheating is a pressure-induced phenomenon which follows the Clausius-Clapeyron relation. It was demonstrated that substantial superheating can be achieved by a pressure build-up even without confinement of epitaxial interfaces for a metal/ceramic system.