Structural evolution and electrical properties of Sc2O3-Stabilized ZrO2 aged at 850°C in air and wet-forming gas ambients

X-ray diffraction (XRD) and electron microscopy investigations have been performed on Sc2O3-stabilized ZrO2 as-sintered and after aging in air or in wet-forming gas at 850 degrees C for 1000 h. Some tetragonal to monoclinic transformation had occurred in the near-surface regions of 4 mol% Sc2O3 samples after aging; the phase transition was more severe for samples aged in the forming gas ambient. A decrease of similar to 20% in electrical conductivity accompanied the aging. In 6 mol% Sc2O3 samples, although no cubic to tetragonal transformation was detected, both the electrical conductivity and the activation energy for ionic conductivity decreased significantly during aging. Ten mole percent Sc2O3 samples did not show appreciable change in electrical conductivity due to aging, although some near-surface cubic to rhombohedral transformation did occur. Sharpening of the (400)(t) XRD peak of Sc2O3-stabilzed tetragonal ZrO2 accompanies the change(s) in the electrical conductivity.