Terbium phosphate
Chemical compound
From Wikipedia, the free encyclopedia
Terbium phosphate is an inorganic compound of terbium and phosphate with the chemical formula TbPO4. Hydrated and anhydrous forms are known. Depending on preparation conditions, anhydrous TbPO4 can occur in both xenotime- and monazite-type structures.
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| Names | |
|---|---|
| Other names
Terbium orthophosphate | |
| Identifiers | |
| ECHA InfoCard | 100.034.171 |
CompTox Dashboard (EPA) |
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| Properties | |
| TbPO4 | |
| Molar mass | 253.89 g/mol |
| Appearance | Solid |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Preparation
Hydrated terbium phosphate can be prepared by precipitation from aqueous solutions containing Tb3+ and phosphate ions. For example, terbium(III) chloride reacts with sodium phosphate to give hydrated TbPO4.[1]
The precipitated hydrate can be converted to anhydrous TbPO4 by calcination at about 800 °C.[1]
Hydrothermal synthesis has also been used to prepare TbPO4·H2O nanostructures with controlled morphologies.[2]
Structure and properties
Terbium phosphate is unusual among the rare-earth orthophosphates because it lies close to the structural boundary between the monoclinic monazite and tetragonal xenotime structure types.
The xenotime form crystallizes in the tetragonal crystal system in space group I41/amd. Xenotime-type TbPO4 is metastable with respect to the denser monazite form under sufficiently high pressure.[3]
Under pressure, xenotime-type TbPO4 transforms to the monoclinic monazite structure. Experiments place the onset of the transformation at about 9 GPa under near-hydrostatic conditions.[4] The transformation is irreversible on decompression.[4]
Hydrated TbPO4 commonly adopts a rhabdophane-type structure. TbPO4·H2O prepared hydrothermally forms nanorods and hierarchical spindle-like aggregates, with morphology strongly dependent on pH and reactant concentrations.[2]
Luminescence
Terbium phosphate shows characteristic Tb3+ photoluminescence. Under ultraviolet excitation, TbPO4 exhibits emission from the 5D4 excited state to the 7FJ ground-state manifold, producing strong green to yellow-green emission.
An early study reported orange-yellow fluorescence under ultraviolet light near 366 nm, with a reversible change to the characteristic yellow-green terbium emission after heating in air to about 100 °C.[5]
Nanostructured TbPO4·H2 also shows strong photoluminescence, with hierarchical spindle-like particles giving greater emission intensity than comparable nano- and microscale particles.[2]
Magnetic properties
TbPO4 orders antiferromagnetically at very low temperature. Recent measurements place the transition near 2.3 K and report a sizeable low-temperature magnetocaloric effect, leading to interest in TbPO4 for cryogenic magnetic refrigeration.[6]