Phase assembly and microstructure of CeO2-doped ZrO2 ceramics prepared by spark plasma sintering

CeO2-doped ZrO2 (8 mol%) starting powder was sintered by means of spark plasma sintering (SPS) at 1300 °C without holding time. The stability of the tetragonal ZrO2 phase in the Ce-ZrO2 ceramic sintered under strongly reducing conditions was investigated. The SPS sample consisted of monoclinic and tetragonal ZrO2 phases with a volume ratio of two to one, as well as a trace amount of a Zr–Ce–O cubic solid solution phase. In contrast, the same powder sintered by hot-pressing in nitrogen at 1300 and 1500 °C for 1 h showed no tetragonal ZrO2. Microstructural observation of the SPS ceramic by SEM and TEM revealed grains with and without twins. The reason for the appearance of the tetragonal phase in the SPS sample sintered under strongly reducing conditions is discussed.