Synthesis, structure and properties of Na[AsW2O9]

Single crystal and polycrystalline powder samples of sodium arseno-tungstate of composition Na[AsW2O9] were synthesized using high-temperature solid-state methods. The greenish single crystals of the phase were characterized by X-ray diffraction data structure determination and the bulk compound confirmed by powder X-ray data Rietveld refinements. Additionally, scanning electron microscopy (SEM) attached with energy dispersive X-Ray spectroscopy (EDX), thermogravimetry (TG), differential scanning calorimetry (DSC), fourier transform infrared (FTIR) and Raman spectroscopy was performed. A comparative study between Na[AsW2O9] and isotypic K[AsW2O9] demonstrates the structural modifications and the consequent properties. Placing sodium in the channel of the arseno-tungstate framework, the average AsO and WO bond distances did not change due to their rigid-unit like behaviors. However, the unit cell volume contracted about 7.4% caused by shrinkage of the channel dimensions due to shorter NaO bond distances. The non-linear optical property of the compound has been explained in terms of asymmetric WO and AsO chemical bonding led by WO6 and AsO4 polyhedral distortion, respectively.