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

• DOI: 10.3390/cryst12070892
• Publication Date: 2022-06-24T01:25:00Z
• Authors: Victor V. Popov; Yan V. Zubavichus; Alexey P. Menushe...; Alexey A. Yastreb...; Bulat R. Gaynanov; Sergey G. Rudakov; Andrey A. Ivanov; Fyodor E. Dubyago; Roman D. Svetogorov; Evgeny V. Khramov; Nadezhda A. Tsarenko; Nataliya V. Ognev...; Igor V. Shchetinin
• Keywords: simultaneous thermal analysis; Crystallography; lanthanoid tungstates; X-ray absorption fine structure (XAFS); QD901-999; lanthanoid tungstates; phase transitions; hydration; synchrotron XRD; X-ray absorption fine structure (XAFS); simultaneous thermal analysis; raman spectroscopy; FT-IR spectroscopy; synchrotron XRD; 01 natural sciences; hydration; phase transitions; 0104 chemical sciences

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.