A diffusion couple of 3 mol% Y2O3-ZrO2 and titanium was isothermally annealed in argon at temperatures between 1100 degrees and 1550 degrees C. The phases and microstructure in the ceramic side were investigated using scanning electron microscopy and transmission electron microscopy, both attached to an energy-dispersive spectrometer. After annealing at 1100 degrees C/6 h, zirconia grains did not grow conspicuously and evolved only traces of oxygen, resulting in t-ZrO2-x but not alpha-Zr. At temperatures above 1300 degrees C, a significant amount of oxygen evolved from zirconia, reducing the O/Zr ratio, such that alpha-Zr was excluded from t-ZrO2-x during cooling, yielding a higher O/Zr ratio (approximate to 2). When held at 1550 degrees C/6 h, zirconia grains grew rapidly. The alpha-Zr was segregated on grain boundaries during cooling by the exsolution of zirconium from ZrO2-x, while twinned t'-ZrO2-x or lenticular t-ZrO2-x, which was embedded in ordered c-ZrO2-x, was found. The ordered c-ZrO2-x was identified by the 1/5 {113} superlattice reflections of its electron diffraction patterns.