Nonequilibrium transitions in driven AB3 compounds on the fcc lattice: A multivariate master-equation approach

We studied the order-disorder transition in an Ising-type alloy on a fcc lattice with AB3 stoichiometry with atomic exchanges due to two competing processes: thermally activated jumps and ballistic jumps, as, for example, is the case under irradiation with high-energy particles. The latter favor disordered configurations, while the former tend to restore a certain degree of order. The state of order is described by a four-dimensional parameter, the occupation of the four simple cubic sublattices into which the fcc lattice may be decomposed. In a mean-field approximation the kinetic equations for the evolution of this order parameter can be found. For a stochastic description, the master equation for the probability of a given state of order is approximated using Kubos ansatz. The resulting partial differential equation is solved taking advantage of symmetry properties of the order-parameter space. A dynamical-equilibrium phase diagram is constructed, and it is shown that new phases, not found under thermal conditions, can be stabilized for a certain model for the saddle-point energy of the thermal jumps.