A metastable state with partially closed regions in Pd₃Al_0.2V_0.8 Alloy

In the kinetic process of the fcc → L1₂ + D0₂₂ phase transition of the Pd₃Al_0.2V_0.8 alloy, the suppression of atomic diffusion in the L1₂ regions during the evolution from the fcc + L1₂ intermediate state occurred under a certain thermodynamic process. Owing to this suppression, the L1₂ regions underwent no L1₂ + D0₂₂ evolution and were closed to atomic exchanges with the fcc regions. As for the fcc regions, the L1₂ + D0₂₂ state indeed formed but the L1₂ chemical composition deviated from that of the L1₂ regions due to a lack of mutual atomic exchange. Such independent evolutions eventually led to a formation of the metastable state with partially closed regions. From the viewpoint of the stochastic process, the L1₂ and fcc regions act as independent closed ensembles with different time averages along the respective probabilistic trajectories during the evolutions. Because the starting state (the fcc single phase) of the phase transition can be regarded as one canonical ensemble, the evolution to the present metastable state indicates a translation from one to two statistical ensembles in one solid state during the phase transition, the trigger for which is the suppression of atomic diffusion in the L1₂ regions.