THE ZIGZAG INTERFACE SHAPE AT THE FERROELASTIC PHASE-TRANSFORMATION

The aim of this article is to analyse the shape of an interface betwee n the paraelastic and ferroelastic phases in the static case when the sample is placed in a temperature gradient. It is shown that the resul ting shape which is often of a zigzag form follows from the competitio n between the free energy induced by the gradient, the elastic-strain energy caused by lattice misfits along the interface and the interface surface energy. The evaluation of these energy contributions is unavo idable when their magnitudes are comparable. In the first step we eval uate the change in elastic energy, which is due to the lattice misfit, for an anisotropic medium as the function of growth of the zigzag int erface between the phases. In the second step we perform a complete an alysis of the zigzag interface in the approximation of an isotropic me dium. As the main result of our analysis we show that the formation of a zigzag interface is energetically favourable when the ratio delta o f the product of surface and chemical energies to the square of elasti c-strain energy is small. When this condition is not satisfied, the in terface remains flat. The analysis shows that depending on the value o f delta a transition between the zigzag interface and the Bat interfac e may exist which is discontinuous. This means that there exists a ran ge of angles characterizing the zigzag shape which is forbidden.