Wall-wall and kink-kink interactions in ferroelastic materials

Kinks interact with other kinks and antikinks elastically in ferroelastic domain walls and other interfaces in ferroic materials. In thin samples, suitable for transmission electron-microscopy, the interaction is purely dipolar with no indication of monopolar or higher order contributions. Kinks and antikinks attract each other while kink-kink interactions are repulsive. When the kinks are situated in two parallel twin walls, they display the same attraction/repulsion. We argue that this interaction constitutes, part or all, the elusive wall-wall interaction in ferroelastics. The dipolar interactions over distances d between the kinks and between walls decay as 1/d2 when the samples have some nanoscale size. Nanoscale samples bend and tilt when kinks are introduced with typical bent regions of some 1 nm and tilt angles of some 1.2 degrees. Multiple kinks will enhance the effect systematically and bent and modulated twin walls are predicted.