LONG-RANGE VERSUS SHORT-RANGE ORDER IN NI3V AND PD3V ALLOYS

Measurements of the short-range-order (SRO) diffuse scattered intensit y show peaks at the [1 1/2 0] and [100] points in Ni3V and Pd3V, respe ctively, although the stable ground state in both systems (D0(22)) is a [1 1/2 0]-type structure. Mean-field theory predicts [1 1/2 0] SRO i n both materials, in contradiction with experiment for Pd3V. The (100) -type SRO in Pd3V has been explained previously as a non-mean-field ef fect. Via a combination of first-principles total-energy calculations and Monte Carlo simulated annealing, we show that non-mean-field effec ts are insufficient to explain the observed SRO of Pd3V. However, the inclusion of electronic excitations leads to a temperature dependence in the interaction energies which correctly explains both the SRO and phase stability in Pd3V and Ni3V.