Structural and electronic behavior of yttrium doped zirconolite ceramic; a potential waste form for burning minor actinides

Abstract

In the study of nuclear materials, zirconolite ceramic doped with yttrium, as a surrogate for minor actinides, is chosen to study the effects of doping on structural and electronic response which are crucial parameters in the determination of the stability and durability of materials under radiation effects. The samples Ca0.9Zr0.9Y0.2Ti2O7 have been synthesized using conventional solid-state route of two-step sintering process. X-ray diffraction and Raman spectroscopy studies are performed on samples to examine the effect of temperatures on formation of phase. The scanning electron microscopy analysis revealed formation of porous micro-structure at 1200 °C while dense-packed morphology at sintering temperature of 1300 °C. Both XRD and Raman spectroscopy on samples sintered at 1300 °C reveal almost single phase (2 M zirconolite) formation with 20% molar concentration of yttrium thus indicating high loading capacity of zirconolite. The formation of 2M-zirconolite phase is also confirmed from Rietveld refinement of the spectra. Analysis of refinement of spectra of sample sintered at 1300 °C indicates substitution of Y3+ ions against both Ca and Zr sites with similar occupancy of ∼10%, while the altered chemical environment is found to affect the bond length. XPS confirms the presence of Y3+ in the structure and illustrates further that oxidation states of all the elements remain unaltered. Finally, the measurements and analysis show that zirconolite can retain its structural integrity by incorporation of 20% molar concentration of yttrium on Ca and Zr sites and can be a promising waste form for burning the minor actinides in advance accelerators.