Cerium(III) arsenate is an inorganic compound of cerium in the +3 oxidation state and the arsenate ion, with the formula CeAsO4. It crystallizes in the monoclinic monazite structure type and is the synthetic analogue of the rare mineral gasparite-(Ce).
Preparation Cerium(III) arsenate has been prepared by a high-temperature solid-state reaction involving cerium(IV) oxide, potassium carbonate and ammonium dihydrogen arsenate.
In the reported synthesis, the starting materials were mixed in a 4:1:3 molar ratio and heated at 1073 K.
Earlier crystal-growth experiments using CeO2 and molten lead pyroarsenate also produced red to amber crystals nominally assigned to CeAsO4, although their coloration suggested that the cerium valence state may not have been purely +3.
Properties Crystal structure CeAsO4 crystallizes in the monoclinic crystal system, space group P21/n (No. 14), with the monazite structure type. The structure is built from CeO8 coordination polyhedra and AsO4 tetrahedra joined by shared corners and edges.
The CeO8 polyhedra and AsO4 tetrahedra form chains parallel to the direction. Each cerium coordination polyhedron is connected to several neighboring arsenate tetrahedra and cerium polyhedra, giving a dense three-dimensional framework.
This structural type is typical of light rare-earth arsenates. In contrast, arsenates of the smaller heavy rare-earth ions more commonly adopt the tetragonal xenotime-type structure.
Relationship to gasparite-(Ce) Natural Ce-dominant arsenate occurs as gasparite-(Ce), a rare mineral with the same monazite-type structure as synthetic CeAsO4.
Natural gasparite-(Ce) is generally a solid solution containing substantial La, Nd and other rare-earth elements rather than ideal pure CeAsO4.
High-pressure single-crystal diffraction on natural gasparite-(Ce) found no structural phase transition up to about 22 GPa. Compression is accommodated mainly by deformation of the rare-earth coordination polyhedra, while the AsO4 tetrahedra remain comparatively rigid.
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