Structural and thermodynamic mixing properties of La1-xNdxPO4 monazite-type solid solutions
Abstract
La1-xNdxPO4 monazite-type ceramics were synthesized by precipitation and sintering. The obtained crystalline powders and pellets were structurally characterized by X-ray diffraction, electron microscopy, and infrared and Raman spectroscopy. The determined unit cell constants agree with published values for the pure end-members ranging from LaPO4 to DyPO4, as well as with values for known mixed monazite-type lanthanide orthophosphates, indicating a homogeneous solid solution. However, Raman spectroscopy shows a change in short-range order and the results of high temperature oxide melt solution calorimetry suggest a subregular solid solution, which requires two Margules parameters to calculate the observed enthalpy of mixing ΔHmix for La1-xNdxPO4 , which is positive and asymmetric and shows a maximum at x = 0.299 (ΔHmix = 7.53 ± 0.01 kJmol-1) at 298 K.
- Publication:
-
Journal of Solid State Chemistry France
- Pub Date:
- February 2019
- DOI:
- 10.1016/j.jssc.2018.11.040
- Bibcode:
- 2019JSSCh.270..470S
- Keywords:
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- Monazite;
- Solid solution;
- Crystal structure;
- Nuclear waste;
- Actinides;
- Enthalpy of mixing