ORDER-DISORDER BEHAVIOR IN A 2-DIMENSIONAL NONLINEARLY POLARIZABLE MODEL

A crossover from displacive to order-disorder behaviour is found in a two-dimensional non-linearly polarizable model with a ferroelectric tr ansition. The dynamics of a shell model with double-well core-shell in teraction is simulated by means of the molecular dynamics technique. S napshots of the lattice displacement pattern reveal the presence of pr ecursor order regions in the high-temperature phase, while the dynamic al structure factor exhibits a quasielastic component in addition to t he ferroelectric soft mode peak. The local particle dynamics is charac terized by two time scales corresponding to the coexistence of inter- and intra-well motions.