The influence of NiO on the stabilization and microstructure of yittria (Y(2)O(3))-stabilized zirconia (ZrO(2)) (YSZ) is examined. Cold-pressed powders comprising varying amounts of NiO, 8 mol% Y(2)O(3), and ZrO(2) were sintered at 1500 degrees C for 4 h. Specimens were subsequently given a 100 h heat treatment at 1500 degrees C. Phase analysis by X-ray diffraction revealed that the presence of NiO leads to a greater amount of cubic phase ZrO(2) for the sintered specimens compared with the control specimens. The cubic ZrO(2) lattice parameter was significantly smaller for specimens containing NiO, revealing that Ni2(+) ions likely enter the cubic ZrO(2) lattice and play a role in decreasing the time and temperature required for stabilization of the cubic phase. A spherical diffusion model was used to estimate the diffusion of Y(3+) and Ni(2+) into ZrO(2). These results are discussed in the context of the role of NiO in the synthesis of YSZ.