The dominant role of electrode-interfaces in flash induced electronic conductivity of rutile single crystals

The electronically conducting state of oxide single crystals in Stage III can be retained at room temperature by special experimental methods, thereby enabling investigations into the science of the flash phenomenon. For example, in-depth electron microscopy of cubic zirconia single crystals has revealed colossal colonies of oxygen vacancies that form their own crystal as seen in selected area electron diffraction; the defect-crystal was congruent with the parent crystal. Here, we present measurements of the electrode–ceramic interface and crystal matrix resistance in the rutile single crystal by the four-point method. Remarkably, the resistance is dominated by the interfaces; in comparison the matrix resistance is negligible. Furthermore, when the flash current is reversed the resistance at the anode switches between high and low values. The effect is reproduced over several cycles. This switching effect is explained by the segregation of cation defects to the anode and the formation of irreversible crystalline oxygen defect colonies at the cathode. The latter is consistent with “blackening” often seen at cathodes. The results highlight the role of segregation of charged defects into space charge layers at metal electrodes in the initiation and propagation of flash in oxides.