Rapid phase transformation of zirconia in the Ni-ScSZ cermet anode under reducing condition

The ionic configurational structure of the zirconia component in cermet anodes was investigated mainly by laser Raman spectroscopy. Two zirconia-based oxides, 10 mol% Sc₂O₃ and 1 mol% CeO₂ stabilized ZrO₂ (10Sc1CeSZ) and 8 mol% Y₂O₃ stabilized ZrO₂ (8YSZ), were used as oxide component in cermet anodes. Powders mixture with nickel oxide were applied on a dense 10Sc1CeSZ electrolyte disk, fired at 1673 K and then treated at 1173 K for 2 h in wet hydrogen to reduce the nickel oxide. In contradiction with XRD results, which indicate that all zirconia-based oxides were present in the cubic phase after treatment, Raman spectroscopy results indicate interesting differences: (1) 8YSZ in the cermets presented cubic symmetry, (2) 10Sc1CeSZ in the fired mixture on the electrolyte presented both cubic and rhombohedral β phase, (3) 10Sc1CeSZ in the reduced cermet anode was identified as tetragonal, and (4) the electrolyte presented the cubic phase before and after the reduction process. It is clear that the 10Sc1CeSZ component in contact with nickel oxide undergoes rapid transformation from cubic or rhombohedral to tetragonal symmetry accompanying the reduction of nickel oxide to nickel metal.