Phase separation in 12 mol% ceria-doped zirconia induced by heat treatment in H2 and Ar

The phase separation in 12 mol % CeO2-ZrO2 ceramic heat-treated in a mixture of H2 and Ar was investigated by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and Raman scattering. After heat treatment at temperatures above 1200 degrees C, the tetragonal solid-solution phase separated into Zr2Ce2O7 and the monoclinic phase. Raman scattering measurements also provided supplementary evidence for the phase separation. XPS showed that the valence change from Ce4+ to Ce3+ predominantly occurred, whereas the reduction from Zr4+ to Zr3+ took place above 1200 degrees C. In this paper it is concluded, that in the highly reduced sample, where the valence changes from Ce4+ (Zr4+ to Ce3+ (Zr3+), the phase separation is noticeably promoted. Below 1000 degrees C the phase separation was suppressed because of no appreciable valence change to trigger the phase separation