Abstract
The temperature evolution of discommensuration (DC) during the heating run through the commensurate-incommensurate (C-I) transition in barium sodium niobate is investigated by means of transmission electron microscopy. It is found that the interaction of DC is attractive over considerable distances, and that frozen-in DC become meandering and collide with each other in the process of reducing the DC density under the influence of thermal fluctuations at a temperature below the lock-in transition. A transient metastable state (or chaotic state) is observed with successive nucleation of DC in the early stages of transition, and later a wavy DC array is formed. DC loops with high density of DC are formed at a temperature above the C-I transition. A qualitative theoretical explanation of the observed characteristics on the evolution of DC is presented based on a Landau theory.
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