Crystal chemical design, synthesis and characterisation of U(IV)-dominant betafite phases for actinide immobilisation.

ABSTRACT: Crystal chemical design principles were applied to synthesise novel U⁴⁺ dominant and titanium excess betafite phases Ca_1.15(5)U_0.56(4)Zr_0.17(2)Ti_2.19(2)O₇ and Ca_1.10(4)U_0.68(4)Zr_0.15(3)Ti_2.12(2)O₇, in high yield (85-95 wt%), and ceramic density reaching 99% of theoretical. Substitution of Ti on the A-site of the pyrochlore structure, in excess of full B-site occupancy, enabled the radius ratio (r_A/r_B = 1.69) to be tuned into the pyrochlore stability field, approximately 1.48 ≲ r_A/r_B ≲ 1.78, in contrast to the archetype composition CaUTi₂O₇ (r_A/r_B = 1.75). U L₃-edge XANES and U 4f_7/2 and U 4f_5/2 XPS data evidenced U⁴⁺ as the dominant speciation, consistent with the determined chemical compositions. The new betafite phases, and further analysis reported herein, point to a wider family of actinide betafite pyrochlores that could be stabilised by application of the underlying crystal chemical principle applied here.

SUBMITTER: Sun SK 

PROVIDER: S-EPMC10293183 | biostudies-literature | 2023 Jun

REPOSITORIES: biostudies-literature