Synthesis, characterization and structural refinement of polycrystalline uranium substituted zirconolite CaZr0.9U0.1Ti2O7

摘要

Ceramic precursors of Zirconolite (CaZrTi2O7) family have a remarkable property of substitution on Zr4+ cationic sites. This makes them a potential material for nuclear waste management in 'synroc' technology. In order to simulate the mechanism of partial substitution of zirconium by tetravalent actinides, a solid phase of composition CaZr0.9U0.1Ti2O7 was synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and nitrates of uranium and zirconium, respectively. Solid-state synthesis was carried out by repeated pelletizing and sintering the finely powdered oxide mixture in a muffle furnace at 1050 degrees C. The polycrystalline solid phase was characterized by its typical powder diffraction pattern. Step analysis data were used for ab initio calculation of structural parameters. The SEM and EDAX analysis also confirm that the zirconolite acts as a host material for uranium. The powder diffraction data of 3500 points for 2 theta = 10-80 degrees has been analysed by GSAS (general structure analysis system) software to obtain the best fit of the observed data points. The uranium substituted zirconolite crystallizes in monoclinic symmetry with space group C2/c (#15). The following unit cell parameters have been calculated: a = 12.5615(13), b = 7.2743(8), c = 11.5103(33) and P = 101.086(14). The calculated and observed values of the intensities, lattice parameters and density measurement show good agreement. The Rietveld analysis and GSAS based calculations for bond distance Ti-O, Ca-O, Zr-O, and O-M-O bond angles were made. The structure was refined to satisfactory completion. The Rp and Rwp were found to be 0.1583 and 0.2097 respectively. The crystal data of the title compound show that increase in U content results in expansion of the zirconolite unit cell.