Synthesis and structure formation of multi-cation A2B2O7 ceramics with Nb5 +, Mo6+, and Sr2+ additives

Abstract

The key issue for complex high-level waste immobilization has been addressed through the synthesis of multi-cation A₂B₂O₇-type ceramics. This study investigates the structure, micromorphology, chemical state, and performance of samples composed of pyrochlore and fluorite, influenced by different cation species. An increase in the number of cation species promotes the formation of disordered fluorite. The incorporation of cations such as Nb⁵⁺, Mo⁶⁺, and Sr²⁺ into the composition (Gd_1/5Nd_1/5Sm_1/5La_1/5Eu_1/5)₂(Hf_1/5Zr_1/5Ti_1/5Ce_1/5Sn_1/5)₂O₇ elucidates the impact of cation variety on structure formation. Irrespective of its oxidation state, Ce consistently favors the generation of pyrochlore. The introduction of Nb⁵⁺ enhances pyrochlore formation, while the addition of Sr²⁺ and Mo⁶⁺ leads to the formation of perovskite phases with contents of 9.2 % and 23.1 %, respectively. Furthermore, the presence of multiple phases induces porosity in the ceramics, resulting in decreased density and increased water absorption. This study provides insights into the complex high-level waste immobilization.