The movements of transition fronts in barium titanate

The ferroelectric transition in barium titanate near T 0 is first order and proceeds at a finite rate by means of transition fronts, which separate stable and metastable regions of the crystal specimen. The structure and the dynamic behaviour of these fronts have been studied by a number of methods, and are reported in two papers. In this paper it is shown that the velocity ν of a front depends on the rate of heating and on the thermal gradients. The results are nevertheless consistent with ν [is proportional to] exp{- β/( T - T 0 )} where T is the temperature at the front. It is suggested that the `reference' temperature T 0 is not quite constant across the crystal. An activation mechanism is discussed and the value of a shape factor for the activation regions is derived.