Mutual electrosurface transfer and phase formation at the MeWO4|WO3 (Me = Ca, Sr, Ba) interface: Electron microscopy data

Abstract

Experiments on solid-phase electrosurface migration through formally inert eutectic WO3|MeWO4 interfaces in symmetric electrochemical cells such as Pt|WO3|MeWO4|WO3|Pt are performed. It is shown that the most significant changes occur at the “cathode” interface (−)Pt|WO3|MeWO4|, where counter electrosurface drawing of WO3 to the inner surface of MeWO4 ceramics (with the formation of two-phase distributed composite WO3|MeWO4) and a much smaller flow of Me2+ components to the WO3 ceramics depth are observed. Scanning and transmission electron microscopy showed the formation of nano- and microscale objects of various shape in grain boundaries’ regions, among which well-faceted nanoobjects shaped as ribbons and rods from a few to hundreds of nanometers thick are noticeable. The Ca and Sr contents in WO3(−) cathode pellets after experiments in cells are determined by X-ray fluorescence analysis, scanning electron microscopy, energy-dispersive analysis, and depth profiling using glow-discharge spectrometry. The data obtained are interpreted based on the concepts of solid-phase electrocapillarity (WO3 migration) and electrochemical intercalation of Me into the WO3 structure.