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, Tot al energy calculations based on an LMTO-ASA Hamiltonian were performed for a series of bcc compounds, from which equilibrium formation entha lpies were computed, A set of effective cluster interactions were fit to these results and then used as input to ternary cluster variation m ethod calculations, The predictions for the B2 to Heusler alloy transi tion agreed well with experiment, as did the low-temperature portion o f an isoplethal section of the ternary phase diagram, Predictions of s ublattice occupations indicated a preference of Ag for the Cd sublatti ce in the phase with B2 symmetry.