Experimental determination of pair interaction energies in a CoPt3 single crystal and phase-diagram calculations

The short-range order in a CoPt3 single crystal at 1083 K was measured usin g neutron diffuse scattering in the (100) and (110) reciprocal planes. The data were used in conjunction with the inverse cluster variation method in order to extract the first four and the sixth effective pair interaction en ergies. The interactions obtained from the experimental short-range order i ntensities are used to calculate the Pt-rich side of the phase diagram usin g the cluster variation method, the order-disorder transition temperature a t the stoichiometric composition by Monte Carlo simulations, and the unrela xed antiphase boundary energies. The agreement with experimental data is ex cellent. Comparison of the CoPt3 pair energies with those similarly obtaine d in Co3Pt by other authors shows an important dependence of the nearest-ne ighbor pair interaction with concentration.