Title: $\mbox{Rb}_{2}\mbox{Ti}_2\mbox{O}_{5-δ}$: A superionic conductor with colossal dielectric constant,
Abstract: Electrical conductivity and high dielectric constant are in principle
self-excluding, which makes the terms insulator and dielectric usually
synonymous. This is certainly true when the electrical carriers are electrons,
but not necessarily in a material where ions are extremely mobile, electronic
conduction is negligible and the charge transfer at the interface is
immaterial. Here we demonstrate in a perovskite-derived structure containing
five-coordinated Ti atoms, a colossal dielectric constant (up to $\mbox{10}^9$)
together with very high ionic conduction $\mbox{10}^{-3}\mbox{S.cm}^{-1}$ at
room temperature. Coupled investigations of I-V and dielectric constant
behavior allow to demonstrate that, due to ion migration and accumulation, this
material behaves like a giant dipole, exhibiting colossal electrical
polarization (of the order of $\mbox{0.1\,C.cm}^{-2}$). Therefore, it may be
considered as a "ferro-ionet" and is extremely promising in terms of
applications.