Crystal chemistry and structures of (Ca,U) titanate pyrochlores
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Date
2010-10-01
Journal Title
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Publisher
Wiley-Blackwell
Abstract
Analysis of multiphase (Ca,U) titanate pyrochlore samples produced under argon or in air, using laboratory X-ray powder diffraction (XRD) and electron microscopy revealed discrete pyrochlore phase compositions, together with either perovskite or rutile impurities. Investigations of these samples using diffuse reflectance and X-ray photoelectron spectroscopies revealed mixed U4+/U5+ oxidation states for argon-annealed samples and U5+/U6+ oxidation states for air-annealed samples. Single-phase (Ca1.25U4+0.25U5+0.50)Ti2O7 (argon) and (Ca1.40U5+0.60)(Ti1.90U6+0.10)O7 (air) compositions were synthesized and characterized using a combination of synchrotron X-ray and neutron powder diffraction. Severe intensity reduction of hkl odd XRD peaks from the sample produced in air was found to be the result of U6+ sharing the Ti site. The refined crystal structures for both single-phase samples were found to be consistent with the compositions and mixed oxidation states observed by the above spectroscopic measurements. Although the normalized uranium leach rate of the argon-annealed sample was found to be approximately twice that of the air-annealed sample, in 7-day Product Consistency Test the durability of both compounds with respect to leaching by water was found to be excellent. Ca releases were in the range of 0.01–0.03 g/L and U releases were <3 × 10−5 g/L. © 2010, Wiley-Blackwell.
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Keywords
Titanates, Pyrochlore, Electron microscopy, X-ray diffraction, Crystal structure, Argon
Citation
James, M., Carter, M. L., Zhang, Z., Zhang, Y., Wallwork, K. S., Avdeev, M., & Vance, E. R. (2010). Crystal chemistry and structures of (Ca,U) titanate pyrochlores. Journal of the American Ceramic Society, 93(10), 3464-3473. doi:10.1111/j.1551-2916.2010.03871.x