Phase relations and high temperature-XRD studies of Gd_(2-x)Nd_xTi_2O_7 solid solutions

摘要

A series of compositions with the general formula Gd_(2-x)Nd_xTi_2O_7 (0.0 ≤ x ≤ 2.0) was prepared by ceramic sintering and characterized by powder XRD. Nd~(3+) has been used as a surrogate for Am~(3+), an actinide found in spent nuclear fuel. One end member, Gd_2Ti_2O_7, had the pyrochlore structure and formed solid solutions with Nd_2Ti_2O_7 up to the nominal composition Gd_(1.2)Nd_(0.8)Ti_2O_7. An increase in lattice parameter was observed as a function of x in the series Gd_(2-x)Nd_xTi_2O_7 in the composition range 0.0 ≤ x ≤ 0.8. Compositions Gd_(2-x)Nd_xTi_2O_7 in the range 0.8 ≤ x ≤ 1.4 were biphasic. From x > 1.6, the solid solutions are monoclinic, isotypic with Nd_2Ti_2O_7. These results were explained based on the radius (r_A/r_B) ratio of the cations. High temperature-XRD studies on cubic pyrochlores showing thermal expansion are reported.