31P Magic Angle Spinning NMR Study of Flux-Grown Rare-Earth Element Orthophosphate (Monazite/Xenotime) Solid Solutions: Evidence of Random Cation Distribution from Paramagnetically Shifted

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• 作者：Aaron C. Palke ; Jonathan F. Stebbins ; Lynn A. Boatner
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：November 4, 2013
• 年：2013
• 卷：52
• 期：21
• 页码：12605-12615
• 全文大小：418K
• 年卷期：v.52,no.21(November 4, 2013)
• ISSN：1520-510X

文摘

We present ³¹P magic angle spinning nuclear magnetic resonance spectra of flux-grown solid solutions of La_1鈥?i>xCe_xPO₄ (x between 0.027 and 0.32) having the monoclinic monazite structure, and of Y_1鈥?i>xM_xPO₄ (M = Vⁿ⁺, Ce³⁺, Nd³⁺, x between 0.001 and 0.014) having the tetragonal zircon structure. Paramagnetically shifted NMR resonances are observed in all samples due to the presence of paramagnetic Vⁿ⁺, Ce³⁺, and Nd³⁺ in the diamagnetic LaPO₄ or YPO₄. As a first-order observation, the number and relative intensities of these peaks are related to the symmetry and structure of the diamagnetic host phase. The presence of paramagnetic shifts allows for increased resolution between NMR resonances for distinct atomic species which leads to the observation of low intensity peaks related to PO₄ species having more than one paramagnetic neighbor two or four atomic bonds away. Through careful analysis of peak areas and comparison with predictions for simple models, it was determined that solid solutions in the systems examined here are characterized by complete disorder (random distribution) of diamagnetic La³⁺ or Y³⁺ with the paramagnetic substitutional species Ce³⁺ and Nd³⁺. The increased resolution given by the paramagnetic interactions also leads to the observation of splitting of specific resonances in the ³¹P NMR spectra that may be caused by local, small-scale distortions from the substitution of ions having dissimilar ionic radii.