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Physics and Chemistry of Minerals

, Volume 35, Issue 10, pp 603–609 | Cite as

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

  • Philippe E. Raison
  • Regis Jardin
  • Daniel Bouëxière
  • Rudy J. M. Konings
  • Thorsten Geisler
  • Claudiu C. Pavel
  • Jean Rebizant
  • Karin PopaEmail author
Original Paper

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.

Keywords

Cheralite Tetravalent actinide phosphates Rietveld analysis Thorium Neptunium 

Notes

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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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Philippe E. Raison
    • 1
  • Regis Jardin
    • 1
  • Daniel Bouëxière
    • 1
  • Rudy J. M. Konings
    • 1
  • Thorsten Geisler
    • 2
  • Claudiu C. Pavel
    • 1
  • Jean Rebizant
    • 1
  • Karin Popa
    • 3
    Email author
  1. 1.European Commission, Joint Research CentreInstitute for Transuranium ElementsKarlsruheGermany
  2. 2.Institut für MineralogieWestfälische Wilhelms-UniversiätMünsterGermany
  3. 3.Department of ChemistryAl.I. Cuza UniversityIaşiRomania

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