COMPUTER-SIMULATION OF ORDER-ORDER KINETICS IN LL(2) SUPERSTRUCTURE

Monte Carlo simulations of 'order-order' relaxations in AB(3) systems with L1(2) superstructure were carried out assuming vacancy mechanism of atomic jumps with constant atomic pair-interaction energy parameter s and the saddle-point energies assigned to jumping atoms. The study w as focused on relaxations following an increase of temperature. The si mulated 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 ene rgy 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 dominat ed by A-atom jumps between different sublattices. In conclusion, it is proposed that the fast component of the disordering relaxations in L1 (2) superstructure is due to highly correlated pairs of A-atom and B-a tom jumps, which occur provided the majority B-atoms are sufficiently mobile. (C) 1997 Elsevier Science S.A.