Synthesis, characterization and structure refinement of sodium zirconium molibdo-phosphate: Na 0.9Zr 2Mo 0.1P 2.9O 12 (MoNZP)

Abstract

Sodium zirconium phosphate (NZP) is a potential material for immobilization of nuclear effluent of reprocessing plants. The crystal structure of molybdenum containing NZP was determined on the basis of powder diffraction data by Rietveld method. It was found that molybdenum could be immobilized into NZP ceramic matrix without significant changes of the three-dimensional framework structure. The crystal chemistry of the title phase has been investigated using General Structure Analysis System (GSAS) programming. The MoNZP phase synthesized by ceramic route at 1050 °C crystallizes in the rhombohedral system (space group R-3 c) with unit cell parameters: a = b = 8.79255(11) Å, c = 22.7495(5) Å and Z = 6. Step analysis of powder X-ray diffraction data has been subjected to Rietveld refinement to arrive at a satisfactory structural convergence of R-factors: R p = 0.0781, R wp = 0.1051 and RF 2 = 0.06328. The inter-atomic distances and bond angles are in good agreement with their standard values. The particle size along prominent reflecting planes calculated by Scherrer's formula ranges between 15 and 78 nm. The polyhedral distortions and valence calculations from bond strength data are also reported. Morphological examination by SEM reveals that the size of almost rectangular parallelepiped crystallites varies between 0.5 and 1.5 μm. The EDX analysis and IR spectroscopy provide analytical evidence of immobilization of molybdenum cation in the matrix.