Annual Report 2009/2010 - JUWEL - Forschungszentrum Jülich

5.11. Raman Spectra of Synthetic Rare Earth Orthophosphates
H. Schlenz, J. Heuser, S. Schmitz, C. Babelot
Corresponding author: h.schlenz@fz-juelich.de
Abstract
Rare earth orthophosphates were synthesized and investigated by raman spectroscopy. The
data were compared to the available literature and the subsequent analysis of all data
revealed new insights into crystal structures of monazite type and their properties,
respectively. Extraordinary correlations between cell parameters and raman frequencies
were observed and will be explained on the basis of crystallographic considerations in the
course of this report.
Introduction
One of the central tasks of nuclear waste management is the immobilization of actinides (U,
Th, etc.) from spent fuel [1,3]. For the immobilization phosphate ceramics including monazite
appear to be ideal [2,4,5], since such phases are able to take up large amounts of actinides
on regular positions in their crystal structures and keep such elements savely and
permanently. Natural monazite, with an age of up to 3.2 billion years, contains up to 27
weight percent UO 2 and ThO 2 , without achieving any significant radiation damage. For this
and other reasons, ceramic monazite phases are potential candidates for future
management strategies. Therefore new ceramic monazite phases shall be synthesized and
structurally characterized by x-ray diffraction and raman spectroscopy. Goal is the
development of new phases for the permanent integration of U and Th and the investigation
of the ongoing operations at an exposure within the crystal structure. In particular the
order to be able to judge the long-term durability. The development of such new ceramics
provides a new option for the safe disposal of nuclear waste.
Experimental
Rare earth orthophosphates of compositions LaPO 4 , CePO 4 , NdPO 4 , SmPO 4 and EuPO 4
were prepared by hydrothermal synthesis and partly subsequently cold pressed and sintered.
See Heuser et al. and Babelot et al. (this issue) for more detailed descriptions of the applied
synthesis routes. Raman spectra were recorded with a Horiba LabRam HR spectrometer.
The spectra were excited with the 632,81 nm line of a He-Ne laser. The samples were mostly
in the form of small crystalline powders. Some difficulties were encountered with the
excitation of electronic bands, especially in the case of Eu orthophosphate, but the observed
additional bands caused by photoluminescence appear only at wavenumbers greater than
1200 cm -1 and therefore do not disturb the structural information available through the
observed raman frequencies at smaller wavenumbers. Raman measurements were also
performed on LaPO 4 and EuPO 4 pellets. Because of the improved crystallinity these spectra
show significantly sharper peaks and reveal more details (see e.g. Fig. 76), respectively.
Some LaPO 4 pellets were irradiated by 400 keV Kr 2+ ions at increasing dose rates in order to
-recoil effects. Subsequently some of the samples were measured by raman
spectroscopy for the detection of potential radiation damage. Using the program SRIM [21]
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