Virtual cathode induced in Rb2Ti2O5 solid electrolyte

• Published in: Solid state ionics 2019-05, Vol.333, p.72-75
• Main Authors: De Sousa Coutinho, Sofia, Federicci, Rémi, Holé, Stéphane, Leridon, Brigitte
• Format: Article
• Language: English
• Subjects: Anodes; Capacitance; Cathodes; Charge distribution; Chemical Sciences; Condensed Matter; Electric fields; Electric properties; Electrodes; Electrolytes; Ion conductor; Materials Science; Perovskite; Physics; Polycrystals; Rubidium titanate; Single crystals; Solid electrolyte; Solid electrolytes; Stress concentration; Strongly Correlated Electrons; Supercapacitor material; Superconductivity; Virtual cathode; Wave propagation
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2019.01.012

Rb2Ti2O5 (RTO) has recently been demonstrated to be a solid electrolyte, producing colossal capacitance when interfaced with metals. In order to understand the mechanisms leading to such colossal equivalent permittivity (up to four orders of magnitude above state-of-the-art values), the charge distribution in RTO is a key feature to be investigated. In the present article, this charge distribution is probed using the pressure-wave-propagation method, in devices made of RTO single crystals or polycrystals sandwiched between two metallic electrodes. Remarkably enough, in both types of samples, negative charges are found to accumulate inside RTO, near the anode, while the electric field near the cathode remains zero. This proves that the ionic carriers are majoritarily negatively charged and provides an explanation for the colossal capacitance. The latter takes place only at the anode while the cathode is virtually shifted into the solid electrolyte. •Pressure pulse propagation measurementsshow that negative charges accumulate near the anode in Rb2Ti2O5 ion conductor.•The charge distribution is found to be qualitatively similar in single crystals and ceramics made of Rb2Ti2O5.•Rb2Ti2O5 experiences a transition from insulator to metal near the cathode, leading to the creation of a virtual cathode.•This effect is responsible for the colossal density of charge and colossal equivalent permittivity found in this material.