Crystal chemistry and high-temperature vibrational spectra of humite and norbergite: Fluorine and titanium in humite-group minerals

Abstract

The humite-group minerals on the brucite-olivine join may be important dense hydrous magnesium silicate (DHMS) phases in the subducting slab. Fluorine and titanium can be incorporated into the crystal structures through the substitution mechanisms (OH)-= Fand Mg 2+ + 2(OH)-= Ti 4+ + 2O 2-. These substitutions have significant effects on the hydrogen bonding behavior in their crystal structures. Crystal structure refinements and in situ high-temperature Raman and Fourier transform infrared (FTIR) measurements were conducted on natural humite and norbergite crystals. Both minerals crystallize in space group Pbnm, and the isobaric Grüneisen parameters for the lattice and SiO 4 internal vibrations are compared with those of chondrodite, clinohumite, brucite and forsterite. For the humite-group minerals, the OH-stretching modes above 3450 cm-1 are affected by local H-H repulsion, whereas the behavior of those below 3450 cm-1 can be explained by Fand Ti 4+ substitutions, either of which may relieve the H-H repulsion effect. The Raman-active OH bands below 3450 cm-1 are affected by Ti 4+ substitution, while the IR-active bands can be affected by either For Ti 4+ substitutions. Based on an analysis of the high-T Raman and FTIR spectra, the OH vibrations above and below 3450 cm-1 behave differently as a function of temperature, and similar behavior has also been observed for other dense hydrous silicate phases in the hydrous peridotite system. Hence, the lengths of the oxygen-oxygen edges in MgO 6 octahedra where protonation can occur become similar to each other at elevated temperatures. This may provide an This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Highly Effective Fe-Doped Nano Titanium Oxide for Removal of Acetamiprid and Atrazine under Simulated Sunlight Irradiation

“…The FTIR spectra of Fe-nTiO2 with different Fe 3+ doping amounts are shown in Figure 1D. The absorption peak at 3450 cm −1 was -OH [26]; this peak of Fe-nTiO2 was higher than that of nTiO2, probably caused by the water crystallization in the Fe-doping process. The peak of the 1635 cm −1 center in all samples comes from the vibration of the hydroxyl group of water molecules, and the peak size is the same [27]; a broad absorption peak at 625 cm −1 was the vibrational peak caused by Ti-O [28].…”

Stability and Thermoelasticity of Diaspore by Synchrotron X-ray Diffraction and Raman Spectroscopy

“…Moreover, dehydration of hydrous minerals also leads to the brittle fracture of plates, triggering medium-depth earthquakes (Zheng, 2019). Therefore, the structural stability and thermoelastic properties of hydrous minerals under high-pressure and high-temperature (high P-T) conditions are often regarded as a window through which to study the geodynamic process of the deep Earth (Nakao et al, 2016;Kakizawa et al, 2018;Liu et al, 2019;Zhang et al, 2019;Liu et al, 2021).…”