ORDER AND DISORDER IN NI3V - EFFECTIVE PAIR INTERACTIONS AND THE ROLEOF ELECTRONIC EXCITATIONS

In situ neutron diffuse scattering experiments were performed on disor dered Ni3V. Effective pair interactions (EPI) were deduced from the me asured short-range order parameters. The EPI were used to predict succ essfully the disordering temperature and the temperature dependence of the excess free energies of two different antiphases in the ordered p hase. We also computed the energy difference between DO22 and L1(2): o ur result is eight times lower than found by electronic structure calc ulations at 0 K. This discrepancy is partly due to electronic excitati ons.