Sofia de Sousa Coutinho

arXiv2026

One-dimensional self-organization of water molecules in proton conducting Andersson-Wadsley titanates

Layered alkali titanates with M 2 Ti 2 O 5 chemical formula (MTO, M=K,Rb) belonging to the Andersson-Wadsley perovskite family spontaneously incorporate water to form MTO.(H 2 O) x compounds, which exhibit superionic conductivity. At very low hydration x, scanning electron microscopy evidences one-dimensional heterogeneous patterns oriented along ___ b that are arranged in an orderly manner. At higher hydration, the material is observed to spontaneously exfoliate by creating (001) surfaces. Simulations carried out using Density Functional Theory reveal an ordered arrangement of the guest water molecules in Rb 2 Ti 2 O 5 , with strong hydrogen bonds between the water molecules and the apical oxygen of the host crystal. At low hydration x, the water molecules form self-organized one dimensional (1D) double chains along ___ b. Further increase of the water content leads to the creation of hydrated (001)-surfaces that are made of densely packed water chains in agreement with the infrared spectroscopy measurements. Rb 2 Ti 2 O 5 exhibits highly anisotropic proton conductivity, with respect to the crystal orientation, with super-ionic conductivity along ___ b reaching 3 mS/cm at room temperature after hydration. The combined observations and simulations suggest that these water chains are thus at the root of fast proton conduction, which is likely powered by a Grotthuss-like mechanism.

cond-mat.mtrl-sci↗

arXiv2018

Virtual cathode induced in Rb2Ti2O5 solid electrolyte

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.

cond-mat.other↗