Role of planar defects and their energies in periodic to quasiperiodic transformations – a Monte Carlo simulation

Abstract

The initial stages of continuous periodic to quasiperiodic transitions are often characterized by the occurrence of two-dimensional defects (faults or antiphase boundaries) in the periodic structures. Considerable experimental as well as theoretical support exists in favor of such transitions in the cases of the β-Mn to octagonal quasicrystal, the σ-phase to dodecagonal quasicrystal, and the Al 5Ti 3 or Al 11Ti 7 phase to a quasiperiodic superlattice structure. The energy of the relevant planar defects is thus expected to play a vital role in these transitions. Monte Carlo simulations involving a continuous change in the antiphase boundary energy were carried out here to probe the atomic structures of the intermediate stages of the periodic to quasiperiodic superlattice transition observed in Al-rich TiAl intermetallics. The results of the simulation explain the observed changes in the electron diffraction patterns and bring out the salient features of the atomic arrangements in the imperfectly ordered near quasiperiodic structures encountered in the transition.