Single-crystal Raman spectroscopy study of dickite

Abstract

Raman spectra were obtained from the (001), (010), and (100) faces of a St. Claire dickite specimen of known orientation. Raman spectra collected from the (010) and (100) faces of dickite are reported for the first time and reveal vibrational features significantly different from the (001) spectra. Variations in intensities of the (⌷⌯) bands in polarized spectra were used to confirm previous band assignments, to determine the shape and orientation of the local Raman tensors for the OH1 and OH3 groups. The most striking polarization effect observed in the (⌷⌯) region of dickite was the behavior of the a(cЈcЈ)ā spectrum relative to Raman and IR spectra of other orientations. Unlike previously reported spectra, the dominant feature in this spectrum was the 3643 cm Ϫ1 band. This large increase in intensity of the 3643 cm Ϫ1 band in comparison with the other (⌷⌯) bands was related to the fact that Raman spectra were recorded from the edge faces of dickite with the electric vector of the incident laser polarized along the c axis. This permitted observation of vibrational modes polarized along the c axis. Raman frequencies of the (⌷⌯) bands assigned to the OH2 and OH4 groups differ from their IR counterparts by 12 cm Ϫ1 , suggesting that these groups may be related by a center of symmetry. For comparison, Raman spectra in the (⌷⌯) region were also obtained from individual micro-crystals of kaolinite that were approximately 5 m across the (001) face.

The Characterization and Quantitative Analysis of Clay Minerals in the Athabasca Basin, Saskatchewan: Application of Shortwave Infrared Reflectance Spectroscopy

“…3b) appears to support the latter model. shows that the SWIR spectra of kaolinite and dickite are distinct at the 1400 and 2200 nm regions; these regions have been assigned to the first harmonic of inner-surface OH stretching fundamental vibration modes and the combination of outer-surface OH stretching overtone and Al-OH bending, respectively (Brindley et al 1986, Johnston et al 1998. It is noteworthy that the morphology of the 1400 nm doublet of the kaolinite spectra changes systematically with crystallinity (Fig.…”

Hydroxyl-Stretching Bands in Curve-Fitted Micro-Raman, Photoacoustic and Transmission Infrared Spectra of Dickite from St. Claire, Pennsylvania

“…In the last case, the edge between the two faces (110) and (110) of the dickite crystal must be placed on the microscope table, which was impossible in our system. To describe the scattering geometry for different orientations of the crystallographic axes, we used the Porto notation (Swanson, 1973) as adapted for the Raman spectrum of a dickite single-crystal by Johnston et al (1998). As suggested by them, the term c' axis is used since the corresponding spectra were collected at 90 ~ from the (001) face, whereas the c axis makes an angle of 96.5 ~ with respect to this face.…”

“…However, since these ratios are confined to a narrow wavenumber range, it is expected that any inaccuracy will be small. Analysis of the local Raman tensor, which was carried out by Johnston et al (1998), was not conducted during this study. The similarity between the trends in this study and in the work of Johnston et al (1998) supports our observations.…”

“…Recently, Johnston et al (1998) studied the Raman spectra of a single crystal of St. Claire dickite. The authors observed six different polarized Raman spectra from the (001), (010) and (100) faces of large dickite crystals.…”

Microstructural Properties of High Level Waste Concentrates and Gels with raman and Infrared Spectroscopies

“…The work of Johnston et al, who recently published definitive single crystal polarized Raman studies of the solid aluminate species gibbsite (26) and the related aluminosilicate species dickite (27), set the stage for high-pressure diamond-anvil-cell-based Raman investigations of these two compounds. These pressure-dependent Raman investigations focused on the rich OH stretching regions of the two minerals.…”