Discovering Perovskite-Derived Tungsten Bronzes from In Situ Diffraction of Electrochemical Rubidium and Cesium Intercalation

Abstract

Perovskite-derived tungsten bronzes are formed from tungsten oxide by electrochemical intercalation of all alkali metals from aqueous solutions. In two steps, we yield two different polymorphs, where the first step is reversible and the second step is irreversible. The electrochemical approach affords precise control of the composition, while ex situ X-ray diffraction and particularly in situ X-ray diffraction allow the analysis of the atomic structure. For the heavy alkali metals, rubidium and cesium, the in situ synchrotron X-ray diffraction experiments reveal in sum four new structures and their formation process. The irreversible deintercalation step yields at room temperature, the α-WO₃ phase, a tungsten oxide polymorph which is thermodynamically only stable above 1073 K. Finally, analyzing the full alkali metal series allows us to conclude that the symmetry and structure of the formed bronzes are dictated by the electron count on the tungsten oxide network and the size of the ions plays a negligible role.