Monte Carlo simulations of order relaxations in L12-ordered Ni3Al had reproduced the simultaneous action of two processes as observed experimentally by residual resistometry. It was shown that the fast process was related to the fast annihilation/creation of nearest-neighbour antisite pairs. These findings were then strongly corroborated by a new super-cell approach of ab initio quantum mechanical calculations describing the simultaneous displacement of Ni and Al atoms on their way to their respective antisite positions. Studies of single jumps suggested that such a cooperative migration of Ni and Al was necessary in order to prevent Al antisites from jumping back into their regular position. Relaxation of neighbouring atoms was taken into account. Thus, a minimum migration barrier of about 3eV was derived which together with the calculated formation enthalpy of a Ni vacancy of 1.5eV amounted to 4.5eV, in remarkable agreement with the high activation enthalpy of 4.6eV as observed experimentally.

First Principles Calculation of Cooperative Atom Migration in L12 Ni3Al. Schweiger, H., Podloucky, R., Wolf, W., Püschl, W., Pfeiler, W.: Materials Research Society Symposium – Proceedings, 2001, 646, N5111-6