Order-disorder transformations in the heusler alloy Cd2AgAu

A sequence of order-disorder phase transformations was studied in the alloy Cd-Ag-Au at or near the Heusler alloy stoichiometry Cd2AgAu. Total energy calculations based on an LMTO-ASA Hamiltonian were performed for a series of bcc compounds, from which equilibrium formation enthalpies were computed. A set of effective cluster interactions were fit to these results and then used as input to ternary cluster variation method calculations. The predictions for the B2 to Heusler alloy transition agreed well with experiment, as did the low-temperature portion of an isoplethal section of the ternary phase diagram. Predictions of sublattice occupations indicated a preference of Ag for the Cd sublattice in the phase with B2 symmetry.