Phase relation studies in the CeO2-Gd2O3-ZrO2 system

The phase relations in the CeO₂-Gd₂O₃-ZrO₂ system have been established after slowly cooling the samples from 1400 °C. Ceria has been used as a surrogate material in place of plutonia. About 80 compositions in Zr_1−xGd_xO_2−x/2, Ce_1−xGd_xO_2−x/2, Ce_1−xZr_xO_2.00, (Zr_0.5Ce_0.5)_1−xGd_xO_2−x/2, (Ce_0.5Gd_0.5)_1−xZr_xO_1.75+x/4, (Zr_0.5Gd_0.5)_1−xCe_xO_1.75+x/4, and (Ce_0.8Zr_0.2)_xGd_1−xO_1.5+x/2 were prepared by a three steps heating protocol. Based on the refinement of the XRD data, several phase regions namely; cubic fluorite type solid solution, C-type solid solution, and various biphasic regions could be delineated. This system showed the existence of a very wide cubic phase field. About 17.5 mol% GdO_1.5 was found to fully stabilize the cubic zirconia. On the other hand ceria did not stabilize the cubic zirconia. The anion-excess gadolinia, i.e., Gd_1−xCe_xO_1.5+x was found to retain the C-type lattite unlike pure gadolinia. The ternary phase relations were mainly characterized by the presence of wide homogeneity ranges of fluorite type or C-type phases.