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•New synthetic Ga,Ge-rich analogue is structure models of tourmalines at high pressure.•Raman bands positions at ambient conditions depend on Ga, Ge contents.•New band of Ge – O ...stretching vibrations occurs at ~ 870 cm−1 in Raman spectra.•Lattice dynamic calculations agree with experimental Raman data.•Ga,Ge-tourmalines Raman spectra are obtained as function of pressure up to 30 GPa.
We present Raman spectroscopic analysis of the synthetic Ga,Ge-rich tourmalines at pressures up to 30 GPa for the first time. Based on the experimental data, we obtained correlation between the Raman band positions and the cation substitutions in the tetrahedral and octahedral sites at ambient conditions. A new band of Ge–O stretching vibrations, which is not common in natural tourmalines, occurs at ~ 870 cm−1. The main Raman bands shift to the higher frequencies with increasing pressure due to decrease in the bond lengths, associated with structural deformations. The lattice dynamic calculated spectra of tourmalines with various compositions resemble those measured experimentally. Analysis of experimental and theoretical data reveals a possible phase transition at ~ 18.4 GPa in the tourmalines with up to 10 wt% Ga2O3 and 9 wt% GeO2.
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•Brunogeierite was synthesized at 650 °C and 100 MPa by hydrothermal method.•Single crystal structure was refined by XRD.•Mössbauer spectrum corresponds to the octahedral position of ...iron ions VIFe2+.•Lattice dynamic calculations agree with experimental Raman data.•Brunogaierite Raman spectra are obtained as function of pressure up to 30 GPa.
We present complex spectroscopic data of the synthetic brunogeierite (Fe2+)2Ge4+O4 with space group Fd3¯m of spinel structure: a = 8.3783 (6) Å, V = 588.12 (13) Å3. Brunogeierite crystals up to 200 μm in size were crystallized by the interaction of a boric acid solution on a metal iron wire in the presence of germanium oxide (GeO2) at 600/650 °C and 100 MPa. Mössbauer spectrum of synthetic brunogeierite consists of the symmetric doublet with the parameters IS = 1.104(1) mm/s and QS = 2.845(1) mm/s, that corresponds to the octahedral position of iron ions (VIFe2+). The Raman spectra of Fe2GeO4 crystal consist of an intense main band at 756 cm−1 and four less intense bands at ∼644, 472, 302, and ∼205 cm−1 at ambient conditions. All five bands inherent in the spectrum of cubic spinel are present and gradual change in high pressure spectra up to 30 GPa. The color of the crystal changes from brown-orange to reddish at the center at 22.7 GPa and became opaque black up to 30.2 GPa. Herewith, in the high pressure spectra, we observed the splitting of some bands and the appearance of additional bands in a wide pressure range (from 1.6 to 30 GPa). The factor group analysis with the lattice dynamics calculation of potential crystal structure distortions shows the decreasing of the structure symmetry to tetragonal or rhombohedral in this pressure range.
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•Krieselite was synthesized at 600 °C and 100 MPa by hydrothermal method.•Single crystal structure was refined by XRD.•The assignment of Ag bands in non-polarized Raman spectra was ...carried out.•Lattice dynamic calculations agree with experimental Raman data.•Krieselite Raman spectra are obtained as function of pressure up to 30 GPa.
Spontaneous crystals of krieselite (Ge analogue of topaz) with the chemical formula Al2(Ge0.75Si0.25)O4(F1.63OH0.37) were synthesized using a thermo-gradient hydrothermal method at a temperature of 600/650 °C and pressure of 100 MPa. The unit cell parameters are: a = 8.9732(8) Å, b = 8.4823(7) Å, c = 4.7379(5) Å, V = 360.62(6) Å3, space group Pnma. The F-/OH– content of the samples was refined by FTIR spectroscopy method. Raman spectroscopy showed the main differences between the spectra of krieselite and topaz at the ambient conditions. The assignment of observed and calculated Ag bands (cm−1) for non-polarized Raman spectra was carried out. Using in situ Raman spectroscopy at high pressures, the dependence of the shift in the position of the main bands of the krieselite Raman spectrum on the pressure was established, and the corresponding paths of pressure induced distortion of crystal structure was assumed. According to the data of Raman spectroscopy, it was revealed that krieselite does not undergo the phase transitions up to 30 GPa. The probable way of crystal structure distortion within the space group Pnma was proposed based on simulation of high-pressure Raman spectra.
—Tourmaline is one of the widest spread minerals in nature and one of the most popular gems and a promising piezoelectric material. The growth of large crystals is today a topical task. Tourmaline ...monocrystals are difficult to synthesize owing to its complex chemical composition, the high chemical stability in hydrothermal solutions, and the low growth rate. The paper reviews recent data on the tourmaline synthesis and the results obtained at the Institute of Experimental Mineralogy, Russian Academy of Sciences.
Based on experiments including in situ studies of the phase composition and states of aqueous–hydrocarbon fluids in synthetic inclusions in quartz, the thermometric data indicating a heterogeneous ...state of fluids at shallow, medium, and great depths of oil- and gas-bearing layers were obtained. It was shown that aqueous–hydrocarbon fluids with an oil content of ≥10 vol % remain heterogeneous even at depths of up to 10–12 km at temperatures of 250–290°С. As is evident from experiments, homogenization in such fluids was achieved at temperatures above 380–400°C. However, such temperatures have not yet been recorded in any of the real oil and gas basins of the world. The results of our studies allow us to hope for the discovery of homogeneous deep deposits of oil and other hydrocarbons in the future.
The conditions and mechanisms of epitaxial growth of quartz-like α-GeO
2
crystals on quartz substrates using an evaporative-recirculation method are considered. Relatively homogenous α-GeO
2
crystals ...weighing up to 200 g are grown at a growth rate of up to 0.3 mm/day. It is established that molecular adhesion (cohesion) at the boundary between the quartz substrate and the overgrown layer of α-GeO
2
cannot prevent its transition to a stable poorly soluble rutile-like phase. This makes it impossible to grow high-germanium quartz single crystals industrially using a mixture of quartz and quartz-like α-GeO
2
as a batch. However, this process can be implemented if other more soluble germanium-containing compounds, such as quartz-like Si-containing germanium-oxide, are found.
We present the results of experimental studies on mineral and phase transformations in the model system K2O(Li2O)-Al2O3-SiO2-H2O-HF at 300 to 600 °C and 100 MPa using the method of univariant ...assemblages. The phase diagrams involve equilibrium curves among topaz, andalusite, muscovite, pyrophyllite, AlF3, and KnAlF3+n built from our experiments, which have allowed us to determine the topaz stability field. Topaz is stable in solutions with HF concentrations from 3·10-3 to 8·10-1 m and with KF concentrations lower than 7.5·10-3 m. As temperature increases, topaz becomes stable at higher HF concentrations. Application of the results to the Akchatau greisen W-Mo deposit provides an explanation of the observed zonation as a manifestation of metasomatic processes and imposes constraints on the mechanism and conditions of formation of the Akchatau deposit as well as on the compositions of the F-rich fluids participating in the greisenization.
Experimental data on the growth and study of high-germanium single crystals with better piezoelectric characteristics and with a working capacity at higher temperatures and pressures in comparison ...with pure quartz are reported.
Ga-bearing tourmaline was originally synthesized in boron, boron–alkaline, and boron–fluorine hydrothermal solutions at a temperature of 600–650°C and pressure of 100 MPa as crystals of spontaneous ...growth and on seeds. The maximal concentration of Ga
2
O
3
in synthetic crystals reaches ~24.5 wt %. In addition to Ga-bearing tourmaline, Ga-bearing topaz crystallizes in boron–fluorine solution. Ga-bearing albite crystallizes in boron–alkaline solutions, whereas no additional phases are formed in pure boron solutions.
