The role of the spatial distribution of local polarization perturbations in the posistor effect onset

The electrical resistance of polycrystalline ferroelectric semiconductors is defined by the potential barriers due to the existence of local charged surface states at crystallite boundaries. The barrier screening depends on the state of the ferroelectric system and is maximal during spontaneous-polarization switching. It is shown in this paper that the local perturbation of the ferroelectric system, resulting from the repolarization and appearing as a domain wall between the regions with different polarization directions, has a zigzag configuration. The electric field in the vicinity of the zigzag domain wall is stabilized and coincides with the coercive field, which provides low potential barriers in the ferroelectric phase compared with the paraelectric phase. The repolarization processes become inefficient in the potential barrier screening at the transition from the ferroelectric to the paraelectric phase. As a result, a sharp increase in the electrical resistance is observed at the ferroelectric-paraelectric phase transition, called the posistor effect.