Nanograins in ferroelectric films

The electromechanical behaviors of ferroelectric films are highly associated with their polarization domain structure and the domain-wall mobility during domain evolution. A polycrystalline ferroelectric film consists of complex grain configuration and crystalline structure that are very likely to affect the polarization dynamics. In particular the grain boundary plays a key role in affecting the ferroelectric properties once the size of the constituent grains reduces below several hundreds of nanometers. In this chapter, we demonstrate the intrinsic and extrinsic effects of the grain boundary with phase-field simulation for nanocrystalline BaTiO₃. We shall show that the existence of low-permittivity grain boundary can directly and indirectly contribute to the grain-size dependence of the ferroelectric properties in nanograined ferroelectrics, including a very special type, the columnar-grained nanocrystalline ferroelectric film. Experimental investigations on nanocrystalline BaTiO3 films support the proposed mechanisms for grain-size- and grain-shape-dependent polarization responses.