Bond Angle Determination by Angular Exafs Study and Debye-Waller Anisotropy in 2d Graphite Intercalation Compounds

Abstract

Spectra of an oriented sample of RbC8 were recorded for a set of angles from 0° up to 40°. For each peak in the Fourier transform, the amplitude ratio permits to calculate the angle of the corresponding [MATH] vector with respect to the plane. The thermal study from 300 K down to 35 K shows a high anisotropy of the Debye-Waller factor, the amplitude of the vibration being larger in the plane. The second stage RbC24 shows a higher static disorder than the first stage RbC8

Sorption of Metal Ions on Clay Minerals

“…For a linearly polarized X-ray beam and a layered compound having a threefold or higher symmetry axis perpendicular to the layer plane, this absorption coefficient can be written (23)(24)(25)(26)29) ␣ ϭ cos 2 ␣ ϩ Ќ sin 2 ␣, [2] where ␣ is the angle between the electric field vector ⑀ and the layer plane (Fig. 1).…”

“…The existence of a threefold or higher symmetry axis normal to the layer plane indicates that the j th shell contains several u j backscattering atoms with the same ␤ uj orientation (except for ␤ uj ϭ 0Њ). Thus, the ͗cos 2 iuj ͘ term can be reduced to a function of only ␣ and ␤ j by averaging the in-plane uj angles (29). This results in…”

Distribution of Fe in the octahedral sheet of trioctahedral micas by polarized EXAFS

“…For a completely random powder, there is no angular variation, and )~ reduces to: z(k) = Z xi(k) 9 J Once again, assuming that the atomic pair possesses at least a threefold axis perpendicular to the layer plane, X is independent of the position of E within the layer plane. Then, averaging upon the in-plane angles, the following formula is obtained (Bonnin et al 1986 (cos 2 0) = cos 2 fi sin 2 ~ + (sin 2 fl cos 2 ~)/2 (7) where fl is the bond angle of absorber-scatterer vector with respect to the direction perpendicular to the layer plane. It is interesting to note here that this relationship is analogous to (1), but unlike the latter, it does not apply to the whole crystal but is restricted to the atomic pair one is interested in.…”

Polarized EXAFS, distance-valence least-squares modeling (DVLS), and quantitative texture analysis approaches to the structural refinement of Garfield nontronite

“…Thus, this formula cannot easily be handled, and requires transformation through the introduction of angles independent of the orientation of layers in the film plane. However, if one assumes that crystallites are perfectly axisymmetrically oriented around the film plane's normal (this will be demonstrated by texture analysis), then cos 2 q is independent of the projection of e onto the film plane, and can be averaged around the film normal (Bonnin et al 1986). Figure 2a shows the coordinate system defining the atomic pair geometry relative to the film plane (X, Y) and e, for a given rotation a of the film around X.…”