Localized electrochemical redox reactions in yttria stabilized zirconia single crystals

Electroreduction effects in yttria stabilized zirconia are investigated by Hebb-Wagner polarization experiments. By performing optical and thermal microscopy on single crystals and thin films during the application of an electric field under vacuum or oxygen-tight sealed conditions, the movement of the reduction front from cathode to anode causing a blackening of the material is monitored. When performing electrocoloration experiments on thin film samples, the progressing reaction of the blackened region was found to be inhomogeneous and evolves as a dendrite-like finger structure. The progression of the blackening fingers follow preferentially the electric field lines and thus are influenced by distortions of the field such as caused by metallic particles embedded in the oxide. In contrast to this, in the first stage of the reduction process no significant influence of mechanically induced dislocations on the morphology or kinetics on the electroreduction can be found. Only after a heavy electroreduction, a localized transformation of the surface region is observed. There is a evolution of highly oxygen deficient ZrOx regions, having a characteristic checked topography pattern on the microscale.