Crystal Chemistry of Rare Earth Phosphates

Rare earth phosphates, encompassing the monazite, xenotime and rhabdophane polymorphs, constitute a versatile class of inorganic materials distinguished by their robust crystal lattices and diverse coordination environments. The trivalent lanthanides (La–Lu) in REPO4 frameworks adopt either nine-coordinate monazite or eight-coordinate xenotime structures, with the choice governed primarily by ionic radius. Hydrated derivatives (rhabdophanes and churchites) introduce structural water into interlayer or channel sites, influencing thermal stability and phase transformations. Subtle lattice strains arising from size mismatches in mixed-cation systems affect vibrational spectra and excess thermodynamic properties, while the rigidity of PO4 tetrahedra underlies resistance to radiation damage. Applications span nuclear waste immobilisation, proton conductors in electrochemical cells, UV-shielding agents in cosmetics and luminescent markers, reflecting the global importance of tuning crystal chemistry for environmental and technological challenges.

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Crystal Chemistry of Rare Earth Phosphates publication trend

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Technical terms

Monazite structure: A nine-coordinate rare earth orthophosphate polymorph stabilised by larger lanthanide ionic radii.

Xenotime structure: An eight-coordinate tetragonal polymorph favoured by smaller rare earth cations.

Rhabdophane: A hydrated rare earth phosphate (REPO4·nH2O) with water occupying channels or interstices.

Churchite: A metastable layered REPO4·2H2O polymorph with interlayer water and needle-like morphology.

Photoluminescence spectroscopy: A technique for probing local coordination and defect structures via light emission from dopant ions.

Proton conductivity: The transport of protons through hydrated phosphate lattices, relevant to electrochemical applications.

References

1. Microstructural investigation of Au ion-irradiated Eu-doped LaPO4 ceramics and single crystals. npj Materials Degradation (2024).
2. A Comparative Study of Cerium(III) and Cerium(IV) Phosphates for Sunscreens. Molecules (2024).
3. Synthesis and structural investigation of churchite-type REPO4·2H2O (RE = Y, Gd, Dy) nanocrystals. Journal of Solid State Chemistry (2022).
4. Evidence for Lattice Strain and Non-ideal Behavior in the (La1−xEux)PO4 Solid Solution from X-ray Diffraction and Vibrational Spectroscopy. Frontiers in Earth Science (2016).
5. Thermodynamics and Stability of Rhabdophanes, Hydrated Rare Earth Phosphates REPO4 · n H2O. Frontiers in Chemistry (2018).
6. Thermal Stability and Proton Conductivity of Rare Earth Orthophosphate Hydrates. International Journal of Electrochemical Science (2014).