Nd3+掺杂钙钛锆石(Ca1-xNdxZrTi2O7+x/2)相变行为的研究OA北大核心CSTPCD

This paper used Nd3+ as a surrogate element of Am3+ to simulate the study of the stable curing effect of zirconolite on the radioactive element Am3+.The phase evolution behavior caused by Ca2+ sites in the lattice of Ca1-xNdxZrTi2O7+x/2 with Nd3+ heterovalent substitution was systematically investigated.The Ca1-xNdxZrTi2O7+x/2(0≤x≤1.0)ceramic samples were prepared by high temperature solid-state synthesis and characterized by XRD,Raman,BSE,and EDS analysis.The experimental results showed that the solid solution content of Nd3+ ion could reach up to 70%(viz.x=0.7)in the zirconolite lattice.This indicated that the Nd3+ ion as a substitution element could effectively simulate Am3+ solidification in the zirconolite lattice.However,as the doping amount of Nd3+(x≤0.3)increased,the disordering of the O2-and Nd3+ ions in the zirconolite-2M lattice increased gradually.On the contrary,the(Ca/Nd)-O chemical bond was slightly shortened.Until x=0.4,the O2-coordination number around some Zr4+and Ti4+ ions changed(ZrO7→ZrO8,TiO5→TiO6),partly the zirconolite-2M structure rearrangement to the zirconolite-4M structure.When x=0.5,all the zirconolite-2M structure was converted into zirconolite-4M structure,and the ordering of the O2-and Nd3+ cations increased again,with the Ti-O chemical bond slightly elongated.With increasing x(x=0.6、0.7),the sample still retained a single zirconolite-4M structure,but the ordering of the O2-and Nd3+ cations gradually decreased.When x =0.7,the Ca2+、Zr4+、Nd3+ ions exhibited a subtle amount of pyrochlore structure arrangement in the sublattice.When 0.8≤x≤0.9,the samples converted to a polyphase coexistence state(Pyrochlore,ZrTiO4 and Nd2(TiZr)4O11).Finally,a single Nd2(TiZr)4O11 solid solution phase was observed when x = 1.0.Further,the composition and microstructure of coexisting phases were verified by BSE and EDS.