Physics and Chemistry of Minerals最新文献

The temperature dependence of the infrared absorption spectra of two Verneuil-grown corundum samples is investigated in the OH stretching range. The spectra display three main bands at 3184, 3232 and 3309 cm^− 1, belonging to the so-called “3309 cm^− 1 series”, as well as two additional bands at 3163 and 3278 cm^− 1 previously reported in some synthetic corundum samples. The anharmonic behavior of the observed bands is analyzed using the pure dephasing model of Persson and Ryberg and depends on the local geometry of the OH defects, which are all associated with Al vacancies. The unexpected increase with temperature in the absorbance of a weak band at 3209 cm^− 1 supports a revised interpretation of both the 3209 and 3232 cm^− 1 bands. These two bands are interpreted as resulting from the low-temperature equilibrium between two Ti-associated OH defects, enabled by the possibility of hydrogen hopping within the Al vacancy. The temperature-dependent properties of the 3278 cm^− 1 band are similar to those of the other Al-vacancy related defects and a comparison with the theoretical properties of selected OH defects suggests that this band corresponds to the association of the H atom with a non-dissociated Al Frenkel pair. Finally, the properties of the band at 3163 cm^− 1 are consistent with its previously proposed association with Si for Al substitution in corundum.

Studies conducted in NaF-containing hydrothermal fluids have shown that the oxide compounds Sb⁵⁺ are unstable at 800 °C, Р_total = 200 MPa and fO₂ (fH₂) specified by Co–CoO and Ni–NiO buffers interact with the Pt material of the ampoule, forming antimony intermetallics with platinum on the inner surface of the ampoule. The formation of the following intermetallics was established through the analysis of data obtained from studies conducted on an electronic microscope: Pt_90.3±0.8Sb_9.7 (~ Pt₁₀Sb), Pt_82.8±1.3Sb_17.2 (~ Pt₅Sb) and Pt_69.2±4.4Sb_30.8. Pt₁₀Sb compound which was obtained on the inner surface of the Pt ampoule is the limiting solid solution of antimony in platinum at 800 °C. It exhibits a cubic crystal system (Fmoverline{3}m) with a lattice constant of a = 3.943(3) Å and forms an underdeveloped surface < 111>. Pt₅Sb compound, presumably hexagonal P6/mmm crystal system with unit cell parameters a = b = 4.56(4), c = 4.229(2) Å, α = β = 90°, γ = 120°, forms a thin film (≤ 10 μm) on the Pt surface and appears to be a metastable phase. The intermetallic compound of Pt₆₉Sb₃₁ is a rapidly cooled melt of appropriate composition.

A mechanism for deep penetration of Sb into the walls of the Pt ampoule is proposed.

The rhenium carbide Re₃C was predicted to be stable under high pressure and expected to have high hardness and low compressibility. In this study, we realise the synthesis of Re₃C at megabar pressures of 105(3) and 140(5) GPa in laser-heated diamond anvil cells and characterise its structure using synchrotron single-crystal X-ray diffraction. The structure of Re₃C has the monoclinic space group C2/m and is built of CRe₇ capped octahedra. Our combined ab initio calculations and quantitative topological analysis support experimental structural data and further deepen the understanding of the chemical bonding in the newly synthesized compound.

Single-crystal Brillouin scattering measurements are important for interpreting seismic velocities within the Earth and other planetary interiors. These measurements are rare, however, at temperatures above 1000 K, due to the fact that the transparent samples cannot be heated by common laser heating systems operating at a wavelength on the order of 1 μm. Here we present Brillouin scattering data on pyrope collected at pressures up to 23.8 GPa and temperatures between 850 and 1900 K using a novel CO₂ laser heating system confined in either a flexible hollow silica waveguide or an articulated arm with mirrors mounted in each junction to direct the laser to the exit point. Pyrope has been chosen because it has been extensively studied at high pressures and moderate temperatures and therefore it is an excellent sample for bench-marking the CO₂ laser heating system. The new high-temperature velocity data collected in this study allow the room pressure thermal parameters of pyrope to be constrained more tightly, resulting in values that reproduce the temperature dependence of the unit-cell volume of pyrope measured in recent studies at ambient pressure. Aggregate wave velocities of pyrope calculated along an adiabat using the thermoelastic parameters determined in this study are larger than those obtained using published values, implying that velocities for many mantle components may be underestimated at mantle temperatures because high temperature experimental data are lacking.

Scandium (Sc) is a rare element that finds uses in modern technologies. Thermodynamic properties of Sc phases could help in the development of innovative technologies to extract Sc from mining waste. In this work, we investigated the FeOOH–ScOOH solid solution with the goethite structure. The end members and five intermediate compositions were synthesized and characterized. The lattice parameters show that the solid solution is non-ideal, with complex behavior induced by the Fe–Sc substitution. The excess unit-cell volume deviates negatively for the Sc-rich region, and positively for the Fe-rich region from the ideal behavior (Vegard’s law). Enthalpies of dissolution were determined by acid-solution calorimetry in 5 mol(cdot hbox {dm}^{-3}) HCl at T = 343.15 K. Enthalpies of mixing ((Delta _{mix}H)), calculated from the experimental data, are small and positive. The available data allow for fitting the data as (Delta _{mix}H = W x (1-x)), with the mixing parameter (W = 15.2pm)1.0 kJ(cdot hbox {mol}^{-1}). Using (Delta _fG^o) of ScOOH from earlier literature, we calculated a Lippmann diagram that shows that Sc should strongly partition into the aqueous phase upon goethite precipitation. The field observations from lateritic profiles show that Sc is primarily harbored by goethite via adsorption. It seems that under weathering conditions, thermodynamically driven partitioning of (hbox {Sc}^{3+}) into the aqueous phases and its subsequent adsorption onto goethite surfaces controls the mobility of Sc in the weathering profiles.

Compressibility and structural evolution of K-cymrite, hexagonal high-pressure KAlSi₃O₈·H₂O, has been studied up to 18 GPa using synchrotron single crystal X-ray diffraction in Ne pressure medium. K-cymrite retains its original symmetry P6/mmm up to a pressure of 7.3 GPa. As the pressure increases from 7.3 to 8.5 GPa, the weak satellite reflections appear on diffraction patterns and remain up to maximum applied pressure of 18 GPa indicating incommensurate modulation. However, main reflections can be still indexed in hexagonal cell and structure successfully solved in initial P6/mmm group. After pressure release, K-cymrite reverts to initial non-modulated single-crystal state. The parameters of third-order Birch-Murnaghan equation of state for K-cymrite are V₀ = 190.45(12) ų, K₀ = 56.5(7) GPa and K₀’ = 3.2(12), with bulk modulus notably deviating from earlier result (K₀ = 45(2) GPa and K₀’ = 1.3(10)) obtained in vaseline media.

High-pressure and high-temperature Raman spectroscopic measurements of synthetic liebenbergite and Ni₂SiO₄ spinel have been conducted up to 22 GPa and 700 ℃, respectively. Isothermal and isobaric mode Grüneisen parameters were calculated based on the observed Raman modes. The intrinsic anharmonicities of liebenbergite and Ni₂SiO₄ spinel were also evaluated. The changes of the asymmetric SiO₄ stretching band of Ni₂SiO₄ spinel in frequency are irreversible under decompression, indicating a potential pressure-induced modification in the crystal structure at elevated pressures. The values of isothermal mode Grüneisen parameters show that the SiO₄ internal vibrations in Ni-rich olivines are more sensitive to the variations of pressure. For spinel-group minerals, the SiO₄ internal vibrations can be less sensitive to the pressure change due to nickel incorporation. In contrast, according to the values of isobaric mode Grüneisen parameters, nickel increases the sensitivity of these vibrations to the variations of temperature. In addition, nickel has distinctive effects on the intrinsic anharmonicities of different vibration modes in both olivine and spinel-group minerals, and therefore alter the thermodynamic properties of their crystal structures.

Due to experimental challenges and computational complexities, limited research has explored high-temperature and high-pressure conditions on mineral vibrations. This study employs the quasi-harmonic approximation (QHA) and density functional theory (DFT) to investigate the impact of temperature and pressure on the structural properties and infrared and Raman vibrational modes of forsterite. The computational process involves determining lattice parameters, optimizing the internal crystal structure, and calculating IR and Raman spectra at various temperature and pressure values, both separately and combined. Results highlight significant anisotropy in forsterite, with the b-axis being most sensitive to temperature and pressure, followed by the c-axis, while the a-axis exhibits greater stiffness. The positions of vibrational modes typically shift to higher frequencies with increasing pressure (average shift of 2.70 ± 1.30 cm⁻¹/GPa) or to lower frequencies with increasing temperature (average shift of − 0.017 ± 0.018 cm⁻¹/K). Modes associated with SiO₄ stretching and bending are less affected by temperature or pressure than translational and rotational modes. A brief investigation into isotope and chemical substitution, as well as cation distribution, in the solid solution (Mg, Fe)₂SiO₄ reveals lower wavenumbers in fayalite modes compared to forsterite modes, attributed to the heavier Fe mass and larger cell parameters. This study establishes a methodology for computing vibrational frequencies under simultaneous temperature and pressure and emphasizes the significant impact of various factors on vibrational modes. Caution is advised when using vibrational modes for identifying compositions within solid solutions.

Studying the anisotropic physical properties of hexagonal closed-packed (hcp) iron is essential for understanding the properties of the Earth’s inner core related to the preferred orientation of the inner core materials suggested by seismic observations. Investigating the anisotropic physical properties of hcp iron requires (1) the synthesis of hcp iron samples that exhibit several distinctive types of strong lattice preferred orientation (LPO) and (2) the quantitative LPO analysis of the samples. Here, we report the distinctive LPO of hcp iron produced from single-crystal body-centered cubic (bcc) iron compressed along three different crystallographic orientations ([100], [110], and [111]) in a diamond anvil cell based on synchrotron multiangle X-ray diffraction measurements up to 80 GPa and 300 K. The orientation relationships between hcp iron and bcc iron are consistent with the Burgers orientation relationship with variant selection. We show that the present method is a way to synthesize hcp iron with strong and characteristic LPO, which is beneficial for experimentally evaluating the anisotropic physical properties of hcp iron.

CaAl₁₂O₁₉, which can incorporate Ti as both Ti³⁺ and Ti⁴⁺ (charge coupled substitution with Mg²⁺), is one of the first minerals to condense from a gas of solar composition and is used as a ceramic. It is variously known as hibonite, calcium hexaluminate (CaO.6Al₂O₃), and CA₆. The lattice parameters and unit cell volumes of Ti-substituted hibonite (P6₃/mmc) with the formulae CaAl_11.8Ti³⁺_0.2O₁₉ and CaAl_9.8Ti³⁺_0.54Mg_0.83Ti⁴⁺_0.83O₁₉ were determined as a function of temperature from ~ 10 to 275 K by neutron powder diffraction. The thermal expansion is highly anisotropic with the expansion in c a factor of ~ 5 greater than that in a. The change in a is approximately equal for the two compounds whereas the change in c is almost 50% larger for CaAl_11.8Ti³⁺_0.2O₁₉. CaAl_11.8Ti³⁺_0.2O₁₉ also exhibits negative thermal expansion between 10 and 70 K. The change in unit cell volume with temperature of both compositions is well described by a two term Einstein expression. The large change in c is consistent with substitution of Ti onto the M2 and M4 sites of the R-block structural unit.