Melting of embedded Pb nanoparticles monitored using high-temperature in situ XRD

Nanometer-sized Pb particles were embedded in Al matrices using ball-milling and melt-spinning techniques. The melting behavior of embedded Pb particles was monitored using high-temperature in situ X-ray diffraction (XRD) around the equilibrium melting temperature of Pb. Pb particles in ball-milled samples formed incoherent interfaces with Al and melted at temperatures below its equilibrium melting point, whereas those with coherent interfaces produced by melt spinning could be much superheated. In both cases, analysis of XRD data indicated that melting took place when the root-mean-square displacement of Pb atoms reached about 10% of their nearest-neighbor atomic distance, suggesting the applicability of the Lindemann melting criterion to nanocrystals. The atomic vibration amplitudes and characteristic Debye temperature of the embedded Pb particles have also been deduced from XRD data and found to vary with their interfacial structures, which is suggested to be the intrinsic reason for the influence of interface on melting.