This study focuses on the investigation of the influence of dissolved nickel on the accelerated degradation of the ionic conductivity of 8YDZ (8.5 mol% Y 2 O 3 -doped zirconia) under reducing atmosphere. In comparison to pure 8YDZ, the degradation of Ni-containing 8YDZ proceeds 50 times faster and is completed after 100 h at 950 o C. The impact of Ni-incorporation into 8YDZ on microstructure and chemistry was studied by light microscopy (LM) and transmission electron microscopy (TEM). After thermal treatment under reducing atmosphere, a characteristic colour change of 8YDZ is observed by LM that is attributed to the in-diffusion (> 50 µm) of Ni into the 8YDZ substrate. TEM dark-field imaging reveals the coarsening of nanoscaled precipitates of the metastable t''-YDZ in cubic 8YDZ which is correlated with the degradation of the ionic conductivity. Since the decomposition rate of 8YDZ is determined by the mobility of Y and Zr, the dissolved Ni must have a strong impact thereon. An explanation based on the reduction of dissolved Ni under reducing operation conditions is proposed. It is based on the strain field which is expected to arise in the vicinity of the Ni-atoms after reduction.
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