Evidence of fluoride oxidation for development of the electrochemically-induced crystallization observed in lead oxyfluoroborate glasses

This work reports on a distinct experimental procedure conceived to closely approach the question of development of crystallization in lead oxyfluoroborate glasses in the presence of an electric field. After proposing earlier that this phenomenon should involve occurrence of redox-type electrochemical reactions occurring at the electrodes, it was in fact recently shown that a direct contact of the glasses with both the cathode and anode revealed essential, provided that crystallization did not develop when ions migration to these electrodes became frustrated. The present study demonstrates that, even in Pt,Ag/Glass/YSZ:PbF2/Ag,Pt-type electrochemical cells subjected to electric field action, where YSZ:PbF2 represents composite-like mixtures (formed by Y2O3-doped ZrO2 and PbF2) placed between the glass and anode, crystallization was observable in given cases. In summary, supported by (micro)structural and electrical characterizations, clear evidence is provided here that, besides Pb2+ reduction at the cathode, crystallization really involves simultaneous F− oxidation at the anode, completing thus the whole redox electrochemical reaction so far postulated. In these cases, F− migration to the anode was achievable following PbF2 percolative-like paths through the YSZ:PbF2 mixtures.