Intrinsic electrostatic effects in nanostructured ceramics

Using atomic-level calculations with empirical potentials, we have found that electrostatic dipoles can be created at grain boundaries formed from nonpolar surfaces of fluorite-structured materials. In particular, the Σ5 (310) / [001] symmetric tilt grain boundary reconstructs to break the symmetry in the atomic structure at the boundary, forming the dipole. This dipole results in an abrupt change in electrostatic potential across the boundary. In multilayered ceramics composed of stacks of grain boundaries, the change in electrostatic potential at the boundary results in profound electrostatic effects within the crystalline layers, the nature of which depends on the electrical boundary conditions. For open-circuit boundary conditions, layers with either high or low electrostatic potential are formed. By contrast, for short-circuit boundary conditions, electric fields can be created within each layer, the strength of which then depend on the thickness of the layers. These electrostatic effects have important consequences for the behavior of defects and dopants within these materials.