Rb2Ti2O5: Superionic conductor with colossal dielectric constant

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 10(9)) together with very high ionic conduction 10(-3) S cm(-1) at room temperature. Coupled investigations of I-V and dielectric constant behavior allow us to demonstrate that, due to ion migration and accumulation, this material behaves like a giant dipole, exhibiting colossal electrical polarization (of the order of 0.1 C cm(-2)). Therefore it may be considered as a "ferro-ionet" and is extremely promising in terms of applications.