Structural stability study of the mixed La0.7-xLuxEu0.3PO4 solid solutions by Extended X-ray Absorption Spectroscopy


Structural stability study of the mixed La0.7-xLuxEu0.3PO4 solid solutions by Extended X-ray Absorption Spectroscopy

Lozano-Rodriguez, M. J.; Arinicheva, Y.; Holthausen, J.; Neumeier, S.; Scheinost, A. C.

Monazite and related solid solutions are considered as potential candidates for the immobilization of actinides for the disposal of high-level nuclear waste. Because of their low solubility, high resistance to radiation damage and high chemical flexibility, phosphate materials are matter of study 1. Recently many efforts have been putting to find effective ways to synthesis and characterize lanthanide phosphates through diverse methods3. However, a deeper understanding on structural determinations concerning the local atomic arrangement of surrogate elements, i.e., europium, in phosphates matrices is still in progress. In order to correlate the high chemical flexibility of monazite/xenotime structures with local atomic ordering, mixed La0.7-xLuxEu0.3PO4 solid solutions (x=0, 0.35, 0.5, 0.7) have been study by Extended X-ray Absorption Spectroscopy. La L1, Eu L3 and Lu L3-edges were measured for each phosphate solid solution series. It has been found that for each measured element, the local atomic environment has tendency to adopt an environment closer to monazite or xenotime depending strongly to the x loading. The results obtained by XRPD, XANES and EXAFS are discussed with respect to its chemical flexibility in potential host matrix for sequestering long-lived radionuclides.

Keywords: EXAFS; phosphate solid solutions; monazite; lanthanides

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