Observation of ion-induced alloy phase formation in an immiscible YTa system

Abstract

Amorphization was achieved by room temperature 200 keV xenon-ion mixing in an immiscible YTa system, which has a positive heat of formation exceeding +40 kJ/mol. In addition, three new metastable crystalline phases, i.e., an fee phase (fee-I) in Y-rich films, an hep and another fee phase (fee-II) in Ta-rich films, were observed at different ion mixing stages. To give a possible explanation to these anomalous alloying behaviors, a Gibbs-free-energy diagram of the system was calculated based on Miedema's model of heat of formation and a method suggested by Alonso. The free energy of the YTa multilayered films containing excess interfacial free energy was also estimated and added into the diagram. It was found that the excess interfacial free energy stored in the multilayered films could increase the initial energetic state of the multilayers and therefore played an important role in ion-induced alloying in this immiscible system.