Theoretical investigation of moganite

Hantsch, Ute; Winkler, Björn; Pickard, Chris J.; Gale, Julian D.; Warren, M. C.; Milman, Victor; Mauri, Francesco

doi:10.1127/0935-1221/2005/0017-0021

Cited by 12 publications

(15 citation statements)

References 55 publications

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“…Arasuna et al (2014) have experimentally observed the phase transformation from hydrous amorphous silica (colloidal silica) to coesite under 5 GPa and 100°C for 1 h. Heaney (1995) considered that the transformation of metastable moganite to quartz often requires tens of millions of years. However, the theoretical investigation of Hantsch et al (2005) showed that moganite maintains its structure at least up to 10 GPa. In the case of temperatureonly treatment, moganite is transformed to β-moganite at 297°C (Heaney and Post, 2001).…”

Section: Structural and Morphological Changes Of Biogenic Hydrous Amomentioning

confidence: 99%

Pressure–induced crystallization of biogenic hydrous amorphous silica

Kyono

Yokooji

Chiba

et al. 2017

Journal of Mineralogical and Petrological Sciences

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Samples of the diatom Nitzschia cf. frustulum, collected from Lake Yogo, Siga Prefecture, Japan, were cultured in the laboratory. Organic components of the diatom cell were removed by washing with acetone and sodium hypochlorite. The remaining frustules were studied by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared (FTIR) spectroscopy, and synchrotron X-ray diffraction. The results showed that the spindle-shaped diatom frustule was composed of hydrous amorphous silica. Pressure-induced phase transformation of the diatom frustule was investigated by in situ Raman spectroscopic analysis. With exposure to 0.3 GPa at 100°C, the Raman band corresponding to quartz occurred at ν = 465 cm −1 . In addition, a characteristic Raman band for moganite was observed at 501 cm −1 . From the integral ratio of Raman bands, the moganite content in the probed area was estimated to be approximately 50 wt%. With increased pressure and temperature, the initial morphology of diatom frustules was totally changed to a characteristic spherical particle with a diameter of about 2 µm. Increasing pressure to 5.7 GPa at 100°C resulted in the appearance of a Raman band assignable to coesite at 538 cm −1 . That is, with compression and heating, hydrous amorphous silica can be readily crystallized into quartz, moganite, and coesite. First-principles calculations revealed that a disiloxane molecule with a trans configuration is twisted 60°with a close approach of a water molecule, which leads to a trans to cis configuration change. It is therefore reasonable to assume that during crystallization of hydrous amorphous silica, an Si-O-Si bridging unit with the cis configuration would survive as a structural defect, and could subsequently crystallize into moganite by maintaining that geometry. This hypothesis is adaptable to the phase transformation from hydrous amorphous silica to coesite as well, because coesite has four-membered rings and is easily formed from hydrous amorphous silica under high pressure and temperature conditions.

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Section: Structural and Morphological Changes Of Biogenic Hydrous Amomentioning

confidence: 99%

Pressure–induced crystallization of biogenic hydrous amorphous silica

Kyono

Yokooji

Chiba

et al. 2017

Journal of Mineralogical and Petrological Sciences

View full text Add to dashboard Cite

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“…This is in contradiction with experiment and DFT results. (Note that it was for α-moganite that a slightly lower enthalpy (0.35 kJ/mol) than for α-quartz was obtained in [8].) Also the distribution of Si-O-Si angles in β-moganite given in Figure 3 of [22] shows unrealistic maxima at 130° and 159°, which contrast with the values 138.5° and 145.5° obtained in [5].…”

Section: αAnd β-Moganitementioning

confidence: 77%

“…The calculations minimized energy with respect to the parameters defining the moganite cell and the Wyckoff positions, starting out with the moganite structure given in [4]. The results of Hantsch et al [8] are given for comparison in column D1. Also they used the functional PBE.…”

Section: Density Functional Theory Calculationsmentioning

confidence: 99%

“…Denote by ∆E the bond enthalpy per mole SiO 2 of moganite compared to α-quartz. Hantsch et al [8] obtained ∆E D1 = − 0.35 kJ/mol, i.e. moganite should be the stable phase according to the sign of ∆E D1 .…”

Section: Density Functional Theory Calculationsmentioning

confidence: 99%

“…Calculations of the moganite structure using density functional theory (DFT) were done by Hantsch et al [8] and by us for the present paper. They correspond to moganite at a temperature of 0 K and will be compared to the experimental data at ambient temperature and to cell-twin model 1, based either on the quartz data of Lager et al [9] at 13 K or on those of Baur [10] at 291 K.…”

Section: Introductionmentioning

confidence: 99%

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Comparison of experimental and theoretical results for the structure and elastic properties of moganite

Grimmer

Delley

2017

Zeitschrift Für Kristallographie - Crystalline Materials

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Moganite, which is monoclinic at ambient temperature, undergoes a displacive transition to an orthorhombic phase at ≈570 K. Whereas the monoclinic phase may be considered as α-quartz that is Brazil twinned along {1 0 1̅ 1} at the unit-cell scale (cell-twinning), the orthorhombic phase cannot be interpreted as a Brazil cell-twin of β-quartz, in contrast to statements made in the literature. The shape of the oxygen tetrahedra in monoclinic moganite has been determined more reliably by density functional theory (DFT) calculations than by experiment: the differences between the various experimental results for the shape of the oxygen tetrahedra at ambient temperature are typically ten times larger than the differences between the DFT results. The DFT calculations suggest that the oxygen tetrahedra in moganite are very close in shape to the oxygen tetrahedra in α-quartz. Among the three DFT calculations considered, the most convincing results for the bond angles in moganite are obtained for the DMol

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