Yttrium arsenate is an inorganic compound of yttrium and the arsenate ion, with the formula YAsO4. At ambient conditions it crystallizes in the tetragonal xenotime or zircon structure type. It is the synthetic analogue and ideal end-member composition of the mineral chernovite-(Y).
Preparation Yttrium arsenate can be prepared by precipitation from aqueous solution followed by heat treatment. In one modern synthesis, arsenic(III) oxide was oxidized with nitric acid, while yttrium oxide was dissolved separately in nitric acid; the resulting solutions were mixed and reacted at about 60 °C.
The precipitated material can be calcined between about 500 and 900 °C to obtain crystalline YAsO4 nanopowders.
Properties Crystal structure At ambient pressure, YAsO4 crystallizes in the tetragonal crystal system, space group I41/amd (No. 141), with the zircon or xenotime structure type.
Representative lattice parameters for chernovite-(Y) and synthetic YAsO4 are approximately a = 7.04 Å and c = 6.27 Å, with four formula units per unit cell.
The structure consists of isolated tetrahedra and eight-coordinate Y3+ ions. It is closely related to the structures of xenotime-(Y), YPO4, and other heavy rare-earth orthophosphates and orthoarsenates.
Natural chernovite-(Y) commonly forms extensive solid solutions with xenotime-(Y), reflecting substitution between and groups.
High-pressure behaviour Under pressure, YAsO4 undergoes a structural transition from the zircon-type phase to a tetragonal scheelite-type phase.
The transition begins at about 8 GPa; the zircon and scheelite phases coexist over several gigapascals, and conversion is essentially complete by about 14 GPa.
First-principles calculations predict that at still higher pressure the scheelite phase should transform to an SrUO4-type structure above roughly 32 GPa, where arsenic becomes six-coordinate.
Natural chernovite-(Y) displays very similar behavior, transforming irreversibly to a scheelite-type phase near 10.5–11 GPa.
Optical properties Pure YAsO4 is a wide-band-gap material. It has also been investigated as a host lattice for luminescent rare-earth ions.
Eu3+-doped YAsO4 nanopowders show the characteristic red emission of Eu3+. In samples calcined between 500 and 900 °C, crystallite sizes increased from approximately 15 to 45 nm, while the emission and excitation spectra changed with crystallite size and dopant concentration.
These properties have led to investigation of YAsO4:Eu3+ as a nanoscale phosphor material.
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