Visualization of oxygen off-stoichiometry in oxide ceramics by cathodoluminescence spectroscopy

In this study, we used cathodoluminescence (CL) to investigate the influence of annealing treatments with different temperatures and atmospheres on oxygen vacancy concentrations in two paradigmatic ceramic oxides, yttria-stabilized cubic zirconia and alumina. Significant stoichiometric differences were seen for surfaces exposed to either oxidizing or reducing atmospheres by comparison with the respective as-sintered samples. In the case of zirconia, monitoring the CL band located at 500 nm enabled us to visualize the trends of oxygen vacancy formation or annihilation, depending on the annealing conditions selected. In the case of alumina, CL mapping could reveal different processes of oxygen vacancy formation, annihilation and migration (towards grain boundaries) as a consequence of annealing procedures conducted in different gas mixtures. Monitoring the CL intensity of the F+ -center in alumina made it possible to assess the complex stoichiometric state developing at the joint interface between a metal and polycrystalline alumina with nanometric resolution.