Discovering\nPerovskite-Derived Tungsten Bronzes from\nIn Situ Diffraction of Electrochemical Rubidium and Cesium Intercalation

Perovskite-derived tungsten bronzes are formed from tungsten\noxide\nby electrochemical intercalation of all alkali metals from aqueous\nsolutions. In two steps, we yield two different polymorphs, where\nthe first step is reversible and the second step is irreversible.\nThe electrochemical approach affords precise control of the composition,\nwhile ex situ X-ray diffraction and particularly in situ X-ray diffraction\nallow the analysis of the atomic structure. For the heavy alkali metals,\nrubidium and cesium, the in situ synchrotron X-ray diffraction experiments\nreveal in sum four new structures and their formation process. The\nirreversible deintercalation step yields at room temperature, the\nα-WO<sub>3</sub> phase, a tungsten oxide polymorph which is\nthermodynamically only stable above 1073 K. Finally, analyzing the\nfull alkali metal series allows us to conclude that the symmetry and\nstructure of the formed bronzes are dictated by the electron count\non the tungsten oxide network and the size of the ions plays a negligible\nrole.