COMPUTER-SIMULATION OF FERROELASTIC PHASE-TRANSITION IN LANBO4

A model of lanthanum orthoniobate which possesses a ferroelastic tetra gonal-monoclinic phase transition is proposed. It contains only one pa rticle per unit cell, but it is constructed consistently with symmetry changes at the phase transition. The model parameters are chosen to r eproduce the bare soft mode, degree of deformation of the tetragonal u nit cell to a monoclinic one, and the phase transition temperature. Th e ferroelastic system with free boundary conditions was simulated by t he molecular dynamics technique, and the second order phase transition was reproduced. The studied annealing process shows formation of the stripe lenticular domain pattern, which has been interrupted by the ap pearance of a temporary band of perpendicularly oriented lenticular do mains. The maps contain W'-type domain walls whose orientations are fi xed only by interplay of potential parameters and not by symmetry elem ents. The simulated domain pattern has the same features as those obse rved by transmission electron microscopy.