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Gadolinium arsenate
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| Names | |
|---|---|
| Other names
Gadolinium(III) arsenate
| |
| Identifiers | |
| Properties | |
| GdAsO4 | |
| Molar mass | 296.17 g/mol |
| Appearance | Colorless crystalline solid |
| Density | 6.082 g/cm3 (calculated, 25 °C) |
| Sparingly soluble in water | |
| Structure | |
| Tetragonal, xenotime type | |
| I41/amd, No. 141 | |
a = 0.71326 nm, c = 0.63578 nm
| |
Formula units (Z)
|
4 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Gadolinium arsenate is an inorganic compound of gadolinium and the arsenate ion, with the chemical formula GdAsO4. It is a colorless, sparingly soluble crystalline solid with the tetragonal xenotime structure type. At very low temperature it becomes antiferromagnetic.[1]
Preparation
[edit]Gadolinium arsenate can be precipitated from aqueous solutions containing gadolinium(III) and arsenate ions. For example, gadolinium(III) chloride reacts with sodium arsenate:
- GdCl3 + Na3AsO4 → GdAsO4↓ + 3 NaCl
This method has been reported as part of systematic preparations of rare-earth arsenates.[2]
A sample used for standard powder-diffraction measurements was prepared from an aqueous solution of gadolinium trichloride and arsenic pentoxide, followed by heating at 900 °C for 30 minutes.[3]
Properties
[edit]Crystal structure
[edit]GdAsO4 crystallizes in the tetragonal crystal system, space group I41/amd (No. 141), with the xenotime or zircon structure type.[3]
At 25 °C, the lattice parameters are a = 7.1326 Å, c = 6.3578 Å with four formula units per unit cell.[3] The corresponding calculated density is 6.082 g/cm3.[3]
The structure consists of isolated AsO3−4 tetrahedra and eight-coordinate Gd3+ ions. GdAsO4 lies within the xenotime-type part of the rare-earth arsenate series.
Solubility
[edit]Gadolinium arsenate is very sparingly soluble in water. A concentration-based solubility-product value of pKsp,c = 21.67 ± 0.04 has been reported.[4]
Magnetic properties
[edit]GdAsO4 is a low-temperature Heisenberg antiferromagnet. Magnetic-susceptibility and heat-capacity measurements between 0.3 and 20 K show an antiferromagnetic transition at 1.262 K.[1]
The magnetic behavior is closely related to that of the isostructural compound GdVO4, although the exchange interactions in the arsenate are weaker.[1]
Measurements in applied magnetic fields indicate that GdAsO4 does not undergo a single simple spin-flop transition. Instead, several field-induced intermediate magnetic phases occur before the spins reach the high-field saturated state.[5]
Vibrational properties
[edit]Polarized Raman spectroscopy of GdAsO4 single crystals shows the expected internal and external vibrational modes of the xenotime-type structure.[6]
References
[edit]- ^ a b c Colwell, J. H.; Mangum, B. W.; Thornton, D. D. (1971). "Low-Temperature Magnetic Susceptibility and Heat Capacity of GdAsO4". Physical Review B. 3 (11): 3855–3861. doi:10.1103/PhysRevB.3.3855.
- ^ Gabisoniya, Ts. D.; Nanobashvili, E. M. (1980). "Synthesis of rare earth metal arsenates". Soobshcheniya Akademii Nauk Gruzinskoi SSR. 97 (2): 345–348.
- ^ a b c d Standard X-ray Diffraction Powder Patterns. National Bureau of Standards Monograph 25. Vol. 4. National Bureau of Standards. 1965. p. 17.
- ^ Firsching, F. Henry (1992). "Solubility products of the trivalent rare-earth arsenates". Journal of Chemical & Engineering Data. 37 (4): 497–499. doi:10.1021/je00008a028.
- ^ Loftus, K. V.; Parsons, M. W. S.; Rosenberg, H. M.; Swithenby, S. J.; Wells, M. R. (1973). "Evidence for a spin flop phase in gadolinium arsenate". Physics Letters A. 45 (6): 471–472.
- ^ Barros, G.; Santos, C. C.; Ayala, A. P.; Guedes, I.; Boatner, L. A.; Loong, C.-K. (2010). "Raman investigations of rare-earth arsenate single crystals". Journal of Raman Spectroscopy. 41 (6): 694–697. doi:10.1002/jrs.2497.