Vibrational and structural properties in the dihydrate sodium tungstate and in the dihydrate sodium molybdate crystals

• Published in: Journal of molecular structure Vol. 1033; pp. 154 - 161
• Main Authors: Saraiva, G.D., Luz-Lima, C., Freire, P.T.C., Ramiro de Castro, A.J., de Sousa, G.P., Melo, F.E.A., Silva, J.H., Mendes Filho, J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 06.02.2013
• Subjects: Crystal structure; crystals; Infrared; Molybdate; Phase transition; Raman; Raman spectroscopy; sodium; sodium molybdate; temperature; Tungstates; X-ray; X-ray diffraction; Raman; X-ray; Infrared; Tungstates; Molybdate; Phase transition
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2012.08.024

► Temperature-dependent Raman and IR. studies have been performed on polycrystalline crystals. ► Temperature-dependent X-ray diffraction studies, have been performed on polycrystalline crystals. ► Raman spectroscopic measurements of Na2WO4⋅2H2O, under hydrostatic pressure was performed. ► The crystals have undergone conformational changes at around 100–120K. ► Raman measurements of Na2WO4⋅2H2O, under hydrostatic pressure undergoes a phase transition. Temperature-dependent vibrational (Raman and infrared) spectroscopy and X-ray diffraction studies have been performed on polycrystalline Na2WO4⋅2H2O and Na2MoO4⋅2H2O crystals. Raman data at low temperature 13–300K for sodium tungstate Na2WO4⋅2H2O was compared with the sodium molybdate Na2MoO4⋅2H2O. The infrared and the X-ray diffraction obtained in the 80–300K suggest that both crystals have undergone conformational changes connected with an increase in the Raman intensity of NaO6 modes and the libration modes of water molecules at about 100–120K. Additionally, Raman spectroscopy measurements of Na2WO4⋅2H2O under hydrostatic pressure (from 0 to 5GPa) were performed. The pressure-dependent studies indicate the starting orthorhombic structure is stable in the 0.0–3.2GPa pressure range, and undergoes a phase transition at about 3.9GPa, associated with rotation of WO4-2 units.