Heterolayers, CaF2/BaF2/CaF2, were prepared by means of molecular beam epitaxy, and the spacing was varied from 1nm to 1μm. At 1μm to 5nm, the conductivity (effective value measured parallel to the interface) increased with the increasing interfacial density. This was true even for spacings in the sub-Debye range. At relatively large spacings (>50nm), semi-infinite space charges provided a quantitative description. The behavior at smaller spacings revealed nano-sized anomalies. At spacings below about 5nm, the conductivity decreased. The results demonstrated the possibility of preparing artificial ion conductors, and the potential of mesoscopic ionic conduction.

Enhanced Ionic Conductivity and Mesoscopic Size Effects in Heterostructures of BaF2 and CaF2. N.Sata, N.Y.Jin-Phillipp, K.Eberl, J.Maier: Solid State Ionics, 2002, 154-155, 497-502