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Structural investigation of the synthetic CaAn(PO4)2 (An = Th and Np) cheralite-like phosphates

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Abstract

The crystallographic structures of the synthetic cheralite, CaTh(PO4)2, and its homolog CaNp(PO4)2 have been investigated by X-ray diffraction at room temperature. Rietveld analyses showed that both compounds crystallize in the monoclinic system and are isostructural to monazite LnPO4 (Ln = La to Gd). The space group is P21/n (I.T. = 14) with Z = 2. The refined lattice parameters of CaTh(PO4)2 are a = 6.7085(8) Å, b = 6.9160(6) Å, c = 6.4152(6) Å, and β = 103.71(1)° with best fit parameters R wp = 4.87%, R p = 3.69% and R B = 3.99%. For CaNp(PO4)2, we obtained a = 6.6509(5) Å, b = 6.8390(3) Å, c = 6.3537(8) Å, and β = 104.12(6)° and R wp = 6.74%, R p = 5.23%, and R B = 6.05%. The results indicate significant distortions of bond length and angles of the PO4 tetrahedra in CaTh(PO4)2 and to a lesser extent in CaNp(PO4)2. The structural distortions were confirmed by Raman spectroscopy of CaTh(PO4)2. A comparison with the isostructural compounds LnPO4 (Ln = Ce and Sm) confirmed that the substitution of the large rare earth trivalent cations with Ca2+ and Th4+ introduces a distortion of the PO4 tetrahedra.

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Acknowledgments

We thank Dr. G. Novitchi (State University, Chisinau, Moldova) for his assistance during the IR measurements. K.P. and C.C.P. acknowledges the European Commission for support given in the frame of program “Training and Mobility of Researchers”. Participation to the European Commission-JRC-ITU Actinide User Laboratory program is also acknowledged.

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Authors and Affiliations

  1. European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, 76125, Karlsruhe, Germany

    Philippe E. Raison, Regis Jardin, Daniel Bouëxière, Rudy J. M. Konings, Claudiu C. Pavel & Jean Rebizant

  2. Institut für Mineralogie, Westfälische Wilhelms-Universiät, Corrensstr. 24, 48149, Münster, Germany

    Thorsten Geisler

  3. Department of Chemistry, Al.I. Cuza University, 11—Carol I Blvd., 700506, Iaşi, Romania

    Karin Popa

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  1. Philippe E. Raison
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  2. Regis Jardin
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  3. Daniel Bouëxière
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  4. Rudy J. M. Konings
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  5. Thorsten Geisler
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  6. Claudiu C. Pavel
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  7. Jean Rebizant
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  8. Karin Popa
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Correspondence to Karin Popa.

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Raison, P.E., Jardin, R., Bouëxière, D. et al. Structural investigation of the synthetic CaAn(PO4)2 (An = Th and Np) cheralite-like phosphates. Phys Chem Minerals 35, 603–609 (2008). https://doi.org/10.1007/s00269-008-0252-4

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