Erbium phosphate is an inorganic compound of erbium and phosphate with the chemical formula ErPO4. Hydrated forms are also known.
Preparation Hydrated erbium phosphate can be prepared by precipitation from aqueous solutions containing Er3+ and phosphate ions. A dihydrate has been obtained by reacting erbium(III) chloride with phosphoric acid.
Heating hydrated erbium phosphate produces anhydrous ErPO4.
Anhydrous material can also be prepared by high-temperature solid-state or hydrothermal methods.
Structure and properties Anhydrous erbium phosphate crystallizes in the tetragonal crystal system with the xenotime structure, which is isostructural with zircon. It belongs to space group I41/amd (No. 141), with four formula units per unit cell. Reported lattice parameters are a = 6.8614(5) Å and c = 6.0082(9) Å.
The structure consists of isolated PO4 tetrahedra and eight-coordinate Er3+ ions. Like other heavy rare-earth orthophosphates, ErPO4 is chemically resistant and only very slightly soluble in water.
Erbium phosphate has a high melting point, reported at approximately 1896 °C. Thermodynamic measurements have been made over a wide temperature range; its heat capacity shows a Schottky anomaly associated with crystal-field splitting of the Er3+ electronic levels.
High-pressure behaviour At ambient pressure ErPO4 adopts the xenotime structure. Under compression it undergoes a reversible structural transformation to a denser monoclinic monazite-type phase, with the transition beginning at about 17.3 GPa.
The monazite phase is less compressible than the xenotime phase because of its more efficient atomic packing.
Reactions Erbium phosphate reacts with sodium fluoride under suitable conditions to form the fluorophosphates NaErFPO4 and Na3Er2F3PO4.Smirnova, I. N.; Gorkovenko, M. Yu.; Zimina, G. V.; Spiridonov, F. M.; Kaloev, N. I.; Komissarova, L. N. "Rare earth fluorophosphates". Izvestiya Vysshikh Uchebnykh Zavedenii, Tsvetnaya Metallurgiya. 1994. 1–2: 71–74.
It also reacts with potassium metaphosphate, KPO3, to form potassium erbium diphosphate, KErP2O7.
References