Structure determination of (Al, Nd)-doped zirconolite grown from CaO-SiO2-Al2O3-TiO2-ZrO2-Nd2O3-Na2O glass

Abstract

Actinides and Pu are the major contributors to the long term radioactivity of high level nuclear waste after disposal. Zirconolite-based glass-ceramics is a promising candidate for immobilizing actinide radionuclides. Thus, it is essential to study the crystal structure of zirconolite grown from the glass matrix. In this study, Nd was used as the surrogate of actinides, and the structure of zirconolite crystals grown from the glass system was first explored. Powder X-ray diffraction (PXRD), transmission electron microscopy – energy dispersive X-ray spectroscopy (TEM-EDS) and selected area electron diffraction (SAED) were used to characterize the sample. Rietveld refinement method was employed to obtain the structural details of this zirconolite phase, and the chemical compositions of the zirconolite crystal were also determined. The PXRD and SAED results show that the zirconolite crystallized in symmetry of space group C12/c1 with a= 12.562(1) Å, b= 7.2546 (6) Å, c= 11.3616 (3) Å, and beta= 100.67º. The occupancy of Nd atoms in different Wyckoff sites was analyzed by the Rietveld refinement of PXRD data and showed that Nd had a higher preference for occupying the Ca sites.