Computer simulation of `order-orderʹ kinetics in L12 superstructure

Monte Carlo simulations of `order-orderʹ relaxations in AB3 systems with L12 superstructure were carried out assuming vacancy mechanism of atomic jumps with constant atomic pair-interaction energy parameters and the saddle-point energies assigned to jumping atoms. The study was focused on relaxations following an increase of temperature. The simulated long-range order (LRO) relaxation curves fitted weighted sums of two exponentials strongly differing in relaxation times, the longer ones of which obeyed the Arrhenius law. The contribution (weight) of the fast process was gradually reduced when the activation barrier energy for B-atom jumps was increased in relation to that for A-atoms. It was found out that the initial stages of LRO relaxations were dominated by A-atom jumps between different sublattices. In conclusion, it is proposed that the fast component of the disordering relaxations in L12 superstructure is due to highly correlated pairs of A-atom and B-atom jumps, which occur provided the majority B-atoms are sufficiently mobile.