Erbium arsenate is an inorganic compound of erbium and the arsenate ion, with the chemical formula ErAsO4. It is a very pale pink, sparingly soluble crystalline solid and crystallizes in the tetragonal xenotime structure type.
Preparation Erbium arsenate can be prepared by precipitation from aqueous solutions containing erbium(III) and arsenate ions. For example, erbium(III) chloride reacts with sodium arsenate:
ErCl3 + Na3AsO4 → ErAsO4↓ + 3 NaCl
This preparation has been reported as part of systematic studies of rare-earth arsenates.
A standard diffraction sample was prepared from an aqueous solution of arsenic pentoxide and erbium trichloride.
Properties Crystal structure At room temperature, ErAsO4 crystallizes in the tetragonal crystal system, space group I41/amd (No. 141), with the xenotime or zircon structure type.
At 25 °C, the lattice parameters are a = 7.0203 Å, c = 6.2761 Å with four formula units per unit cell. The calculated density is 6.574 g/cm3.
The structure consists of isolated tetrahedra and eight-coordinate Er3+ ions. The NBS sample was described as very pale pink.
ErAsO4 belongs to the heavy rare-earth arsenate series, whose members generally adopt the tetragonal xenotime structure rather than the monoclinic monazite structure found for the largest rare-earth ions.
Solubility Erbium arsenate is very sparingly soluble in water. A concentration-based solubility-product value of pKsp,c = has been reported.
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