A systematic investigation of the phase assemblage and microstructure of the zirconolite CaZr1-xCexTi2O7 system

A series of zirconolite ceramics with nominal stoichiometry CaZr1-xCexTi2O7 (0.0 ≤ x ≤ 0.4) were synthesised under oxidizing, inert and reducing conditions, by a conventional solid-state cold press and sinter method. The evolution of phase assemblage and microstructure were characterized by XRD, SEM-EDS, Ce-L3 XANES and Raman spectroscopy techniques. It was determined that the relative yield of zirconolite-2M and zirconolite-4M polytypes, alongside secondary perovskite phases, was influenced by processing environment via the control of Ce3+/4+ speciation. Oxidizing conditions produced a mixture of zirconolite-2M and zirconolite-4M polytypes due to the formation of Ce4+. Inert and reducing conditions yielded predominantly zirconolite-2M and a Ce-bearing perovskite phase through favouring Ce3+ speciation.