An infrared investigation of the otavite-magnesite solid solution
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Fiona A. Bromiley
und
Ming Zhang
Abstract
The local mixing and ordering behavior of the otavite-magnesite solid solution has been characterized using infrared powder absorption spectroscopy in the spectral region 50.2000 cm-1 at room temperature. Lattice modes due to Cd translations (75-200 cm-1) and Mg translations (200-350 cm-1) were both observed in the IR spectra for samples of intermediate composition. Peak positions of Cd translations remain constant as a function of composition, whereas those of Mg translations decrease in wavenumber with increasing otavite content. This suggests that the otavite-magnesite solid solution displays a combination of one-mode and two-mode behavior, most likely due to the large difference in atomic weight between magnesium and cadmium. Vibrational bands relating to the CO32- groups in the spectral region 600-900 cm-1 vary linearly as a function of composition and are not sensitive to the degree of order. The vibrational band at ~1400-1450 cm-1 also varies linearly with composition, but R3 ordered samples show a marked increase in frequency compared to their R3c counterparts. Positive deviations from linearity are observed for the effective line width determined using the autocorrelation method (expressed in terms of Δcorr values) for both lattice modes and bending vibrations of the CO32- molecular groups, whereas a linear variation as a function of composition of the Δcorr values of the CO32- stretching mode is observed for the 800 °C solid solution. Only in the region 600.900 cm.1 is an effect of order observed as a reduction in Δcorr values with respect to the sample with R3c symmetry. The difference in Δcorr values between the ordered and disordered samples was used to determine the local order parameter, q, which is consistent with a tricritical order-disorder transition.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Single-crystal FTIR and X-ray study of vishnevite, ideally [Na6(SO4)][Na2(H2O)2](Si6Al6O24)
- Crystallographic texture and microstructure of terebratulide brachiopod shell calcite: An optimized materials design with hierarchical architecture
- High-temperature phase relations and topological constraints in the quaternary system MgO-Al2O3-SiO2-Cr2O3: An experimental study
- Tilt and buckling modes, and acoustic anisotropy in layers with post-perovskite connectivity
- Optical absorption study of natural garnets of almandine-skiagite composition showing intervalence Fe2+ + Fe3+ → Fe3+ + Fe2+ charge-transfer transition
- Deriving formation constants for aqueous metal complexes from XANES spectra: Zn2+ and Fe2+ chloride complexes in hypersaline solutions
- Birnessite polytype systematics and identiÞ cation by powder X-ray diffraction
- Improved measurement of fission-track annealing in apatite using c-axis projection
- Improved modeling of fission-track annealing in apatite
- Intercalibration of FTIR and SIMS for hydrogen measurements in glasses and nominally anhydrous minerals
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