Features of the Phase Preferences, Long- and Short-Range Order in Ln2(WO4)3 (Ln = Gd, Dy, Ho, Yb) with Their Relation to Hydration Behavior

• Published in: Crystals (Basel) Vol. 12; no. 7; p. 892
• Main Authors: Popov, Victor V., Zubavichus, Yan V., Menushenkov, Alexey P., Yastrebtsev, Alexey A., Gaynanov, Bulat R., Rudakov, Sergey G., Ivanov, Andrey A., Dubyago, Fyodor E., Svetogorov, Roman D., Khramov, Evgeny V., Tsarenko, Nadezhda A., Ognevskaya, Nataliya V., Shchetinin, Igor V.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.07.2022
• Subjects: Crystal structure; Crystallization; Dysprosium; Gadolinium; Hydration; Infrared analysis; Infrared spectroscopy; lanthanoid tungstates; Molecular structure; Phase transitions; Precursors; Radiation; Short range order; simultaneous thermal analysis; Spectrum analysis; Synchrotron radiation; synchrotron XRD; Synchrotrons; Temperature; Thermal analysis; Tungstates; X ray absorption; X ray powder diffraction; X-ray absorption fine structure (XAFS); United States > US; Russia
• ISSN: 2073-4352; 2073-4352
• DOI: 10.3390/cryst12070892

The effect of synthesis conditions on the features of the long- and short-range order of Ln2(WO4)3 (Ln = Gd, Dy, Ho, Yb) powders synthesized via coprecipitation of salts has been studied by a complex of physico-chemical techniques including synchrotron X-ray powder diffraction, X-ray absorption spectroscopy, Raman and infrared spectroscopy, and simultaneous thermal analysis. It was found that crystallization of amorphous precursors begins at 600 °C/3 h and leads to the formation of the monoclinic structure with sp. gr. C12/c1(15) for Ln2(WO4)3 (Ln = Gd, Dy) and with sp. gr. P121/a1(14) for Ln = Yb, whereas crystallization of Ho precursor requires even higher temperature. After annealing at 1000 °C, the P121/a1(14) phase becomes the dominant phase component for all heavy lanthanoid types except for Ln = Gd. It was shown that the Ln (Ln = Dy, Ho, and Yb) tungstates with the P121/a1(14) monoclinic structure correspond to trihydrates Ln2(WO4)3·3H2O formed due to a rapid spontaneous hydration under ambient conditions. It was concluded that the proneness to hydration is due to a specific structure of the P121/a1(14) phase with large voids available to water molecules. Modifications in the local structure of Ln-O coordination shell accompanying the structure type change and hydration are monitored using EXAFS spectroscopy.