Rb2Ti2O5 : 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 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 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.

Memory effects in the ion conductor Rb2Ti2O5

“…In this case, ions are not accumulated and there is no building up of charge at the interface. This is in contradiction to what is observed in the present system where ions remain accumulated, a giant polarization (of the order of 0.1 C cm −2 ) is created 14 , and where no particular gas production is observed at the anode. Moreover, the phenomenon is also observed under helium atmosphere, which discards a possible role played by oxygen gas production and absorption.…”

“…Because of the diffusion force coming from the ionic concentration gradient, the ions motion is getting slower and slower. This regime is nothing but the appearance of the Warburg diffusion 23,24 , caused by the ionic accumulation and already observed in the low-frequency behavior of the dielectric constant 14 . Before the mobile ions begin to feel the edges of the sample they are in a free motion regime with a conductivity of 10 −4 S cm −1 related to the ionic conductivity 14 .…”

“…Recent studies have shown remarkable electrical transport properties in Rb 2 Ti 2 O 5 (RTO) crystals or ceramics 14 . An ionic conductivity up to 10 −3 S cm −1 between 200 K and 330 K was found, making the RTO a superionic conductor in this temperature range.…”

“…An ionic conductivity up to 10 −3 S cm −1 between 200 K and 330 K was found, making the RTO a superionic conductor in this temperature range. Ionic transport in this highly electronically-insulating material creates accumulation of ions at the edges of the system, giving rise to an unscreened macro-dipole with a polarization larger than 0.1 C cm −2 and a colossal equivalent relative permittivity of about 10 8 at low frequency 14 . The possibility of a conventional ferroelectric phase associated to a structural phase transition was completely discarded by Raman spectroscopy and XRD measurements.…”

TiO2–SrTiO3 Biphase Nanoceramics as Advanced Thermoelectric Materials

“…Probably, V O ′′ will be associated with a cation vacancy forming (V Ti ′′′′ + 2V O ′′) complex, namely, the Shottky defect. Federicci et al in [177] reported a superionic conductor with a colossal dielectric constant for Rb 2 Ti 2 O 5 materials annealed under an oxygen-depleted atmosphere (such as He, N 2 , vacuum). They found that oxygen vacancies are created in the material, and the dielectric constant reaches the unprecedented value of 10 9 .…”