Neutron Diffraction Refinement of CaWO4

Abstract

The CaWO4 structure has been refined, starting with the parameters of Sillén and Nylander, using two zones of neutron diffraction data. The oxygen coordinates with the origin of the cell at the W atom (4̄) are x=0.2413 (σ=0.0005), y=0.1511 (σ=0.0006), z=0.0861 (σ=0.0001). The slightly distorted WO4 tetrahedron contains a W–O distance of 1.788 Å (σ=0.003) and angles of 113° 27′ (σ=14′) and 107° 56′ (σ=0.09′). Close nonbonded approaches are Ca–O=2.48 Å and O–O=2.77 Å. Anisotropic thermal vibration parameters were also determined.

The crystal structure of Ca3WO6Cl2 and the configuration of the WO54− ion

“…The W-O(1) bond is much shorter and corresponds to THE CRYSTAL STRUCTURE OF CaaWOsCl2 short octahedral bonds or to bonds found in WO4 tetrahedra, e.g. 1.785 or 1.788 A in CaWO4 [Burbank (1965), from data of Kay, Frazer & Almodovar (1964), or from data of Zalkin & Templeton (1964) (Hess & Hartung, 1966); 2.311 A in WO2C12 (Jarchow, Schr6der & Schulz, 1968).…”

“…The coordination of Ca by O atoms is fourfold with the exception of Ca (2) [Burbank (1965), from data of Kay, Frazer & Almodovar (1964), or from data of Zalkin & Templeton (1964)]; in CAC12.4H20, where CI and O atoms surround the Ca, Ca-O lengths range from 2.352 to 2.468 A (Thewalt & Bugg, 1973). The lengths of the Ca-C1 bonds agree well with the 2.70 to 2.76 A observed in CaClz (Wyckoff, 1948), while the unique Ca(1)-CI(1) bond is somewhat longer but again shorter than bonds in CaCI2.4H20 (2.842 and 2.853 A).…”

DEGRADATION OF METHYLENE BLUE UNDER SOLAR LIGHT USING QUARTZ – Bi2WO6 NANOCOMPOSITES

“…Metal tungstates, such as Y 2 WO 6 [9,10], Bi 2 WO 6 [11], CaWO 4 [12,13] and ZnWO 4 [14,15], are investigated widely in a very long time because of their electric, optical and environmental applications.…”

Pycnometric and Spectroscopic Studies of Red Phosphors Ca2+(1-1.5x)WO4:Eu3+xand Ca2+(1-2x)WO4:Eu3+x,Na+x

“…The host material CaWO 4 exhibits a bright blue fluorescence upon exposure to a short wavelength ultraviolet radiation (254 nm). CaWO 4 crystallizes in the tetragonal scheelite structure (space group: I4 1 /a), [2][3][4][5][6] at ambient temperature and pressure. Calcium tungstate is essentially an ionic compound.…”