Structural-phase transformations in a Cu3Pt alloy during atomic ordering

A complex structural-phase state is revealed by Monte Carlo investigations in a Cu3Pt alloy during the order–disorder transition, which involves atomic ordering and structural transformation. Under thermal cycling of the alloy, its plot for the difference between the free energies per atom in the disordered and partially ordered states has a hysteresis loop. An analysis of the temperature dependences of the difference between configurational energy and combinatorial entropy of a partially disordered state shows that it is the internal energy that plays the leading part rather than the system’s entropy. Under thermal cycling, there is a hysteresis loop in the region of low stability states of the system, the loops being also observed both in the configurational energy plots and those of the combinatorial entropy: under heating and cooling the system is found to be in differing structural-phase states. The region of low-stability states is noted by peculiar domain structure: a so-called tangled domain structure indicating the absence of predominating phases or domains. This tangled domain structure evidences of a thermodynamically indefinite structural state of the system, at which the symmetry of its structural components could be different. The thermodynamic stimuli of a transformation are very few, which results in a wide range of possible structural states observed in the system.