Effect of Shape on Solid-Liquid Phase Changes of Xe Precipitates in An Al Matrix

It is well known that rare-gas Xe atoms embedded in a crystalline Al matrix form precipitates having cuboctahedral shapes bounded by ﹛100﹜ and ﹛111﹜ surfaces1. Below a certain critical size, Xe precipitates are observed to be solid, even at room temperature. This is a result of the Laplace pressure, which is inversely proportional to the radius of the precipitate. Donnelly et al. reported that the critical size of Xe solidification was expected at 4nm in radius at room temperature. Using high-resolution transmission electron microscopy, it is possible to observe these particles directly. It has been demonstrated that under off-Bragg conditions, the Al lattice fringes are minimized whereas the Xe lattice fringes are maximized. From such observations, it was confirmed experimentally that the average critical size of Xe precipitates is around 4 to 5nm in radius. However, much larger Xe precipitates are sometime observed to remain solid.