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.
Preparation 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.
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.
Properties Crystal structure GdAsO4 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 = 7.1326 Å, c = 6.3578 Å with four formula units per unit cell. The corresponding calculated density is 6.082 g/cm3.
The structure consists of isolated tetrahedra and eight-coordinate Gd3+ ions. GdAsO4 lies within the xenotime-type part of the rare-earth arsenate series.
Solubility Gadolinium arsenate is very sparingly soluble in water. A concentration-based solubility-product value of pKsp,c = 21.67 ± 0.04 has been reported.
Magnetic properties 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.
The magnetic behavior is closely related to that of the isostructural compound GdVO4, although the exchange interactions in the arsenate are weaker.
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.
Vibrational properties Polarized Raman spectroscopy of GdAsO4 single crystals shows the expected internal and external vibrational modes of the xenotime-type structure.
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