Author:

Keywords:

Science & Technology, Physical Sciences, Chemistry, Inorganic & Nuclear, Chemistry, Physical, Chemistry, Monazite, Solid solution, Crystal structure, Nuclear waste, Actinides, Enthalpy of mixing, HIGH-TEMPERATURE CALORIMETRY, RAMAN-SPECTRA, CERAMICS, THERMOCHEMISTRY, DIRECTIONS, PROGRESS, SPECTROSCOPY, NMR, GD, LN, 0302 Inorganic Chemistry, 0303 Macromolecular and Materials Chemistry, 0306 Physical Chemistry (incl. Structural), Inorganic & Nuclear Chemistry, 3402 Inorganic chemistry, 3403 Macromolecular and materials chemistry

Abstract:

© 2018 Elsevier Inc. 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±0.01kJmol−1) at 298 K.