A statistical-thermodynamic modeling of behavior and properties in thin-film intermetallic L12-structures

A statistical-thermodynamic model based on a defect correlation model (DCM) is proposed for the description of ordering phenomena and thermodynamic behavior in nano-crystalline thin-film materials with L12-structure, taking into account the presence of vacancies and anti-structure atoms in the structure. It includes a description of both long-range ordering and short-range ordering. Adjustable parameters for the model are the interaction energies between nearest neighbors for which limited information is available in the literature. The variation of defect concentrations, ordering tendency and thermodynamic activities as a function of the number of monoatomic layers, temperature and composition is derived. The theoretical results are tested with experimental data for the bulk intermetallic phases Ni3Ga and Ni3Al. In Ni3Ga, the bulk behavior is approached with approximately 300 layers, whereas in Ni3Al, this happens already with approximately 100 layers.