Motion of 90° and 180° ferroelectric domain wall structures

An analysis of complex 90° and 180° domain wall structures is presented, taking as a departure point the behaviour of a 90° domain wall structure. When contour conditions are taken into account, “180° inclusions” must take a cylinder-like shape, parallel to the mean polarization vector. The volume ratios can be described by only two parameters, denoted as α and β. The domains can be structured by following different patterns leading to different connectivity, and geometrical parameters can be defined in each case. When an action is applied, the response depends on the connectivity, on the geometrical parameter, and on α and β. Due to the coupling between 180° and 90° domain walls, a motion of the former can induce a motion of the latter, so that 180° walls are also involved in the piezoelectric effect. A mechanism of ageing and fatigue is suggested, which is based on the evolution of the domain shape.