Phase relations and high temperature-XRD studies of Gd2−xNdxTi2O7 solid solutions

A series of compositions with the general formula Gd2−xNdxTi2O7 (0.0 ≤ x ≤ 2.0) was prepared by ceramic sintering and characterized by powder XRD. Nd3+ has been used as a surrogate for Am3+, an actinide found in spent nuclear fuel. One end member, Gd2Ti2O7, had the pyrochlore structure and formed solid solutions with Nd2Ti2O7 up to the nominal composition Gd1.2Nd0.8Ti2O7. An increase in lattice parameter was observed as a function of x in the series Gd2−xNdxTi2O7 in the composition range 0.0 ≤ x ≤ 0.8. Compositions Gd2−xNdxTi2O7 in the range 0.8 ≤ x ≤ 1.4 were biphasic. From x ≥ 1.6, the solid solutions are monoclinic, isotypic with Nd2Ti2O7. These results were explained based on the radius (rA/rB) ratio of the cations. High temperature-XRD studies on cubic pyrochlores showing thermal expansion are reported.