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The unit-cell parameters and volumes of geikielite (MgTiO3) and ilmenite (FeTiO3) were investigated at high temperatures up to 700 K and ambient pressure, using in-situ angle-dispersive synchrotron X-ray diffraction. No phase transition was detected over the experimental temperature range. Using (Berman in J Petrol 29:445–522, 1988. 10.1093/petrology/29.2.445) equations to fit the temperature-volume data, the volumetric thermal expansion coefficients at ambient conditions (αV0) of MgTiO3 and FeTiO3 were obtained as follows: 2.55 (6) × 10–5 K−1 and 2.82 (10) × 10–5 K−1, respectively. We infer that the larger effective ionic radius of Fe2+(VI) (0.78 Å) than that of Mg2+(VI) (0.72 Å) renders FeTiO3 has a larger volumetric thermal expansivity than MgTiO3. Simultaneously, the refined axial thermal expansion coefficients under ambient conditions are αa0 = 0.74 (3) × 10–5 K−1 and αc0 = 1.08 (5) × 10–5 K−1 for the a-axis and c-axis of MgTiO3, respectively, and αa0 = 0.95 (5) × 10–5 K−1 and αc0 = 0.92 (12) × 10–5 K−1 for the a-axis and c-axis of FeTiO3, respectively. The axial thermal expansivity of MgTiO3 is anisotropic, but that of FeTiO3 is nearly isotropic. We infer that the main reason for the different axial thermal expansivity between MgTiO3 and FeTiO3 is that the thermal expansion mode of the Mg-O bond in MgTiO3 is different from that of the Fe–O bonds in FeTiO3. [ABSTRACT FROM AUTHOR]

Experimental studies on the phase transition and thermoelastic behavior of barite-group minerals are crucial to understand the recycle of sulfur in Earth's interior. Here, we present a high-pressure and high-temperature (high P–T) study on two barite-group minerals—barite (BaSO4) and celestite (SrSO4) up to ~ 59.5 GPa 700 K and ~ 22.2 GPa, 700 K, respectively, using in situ synchrotron-based X-ray diffraction (XRD) combined with diamond anvil cells (DACs). Our results show that BaSO4 undergoes a pressure-induced phase transition from Pbnm to P212121 at ~ 20.3 GPa, which is different from the previous results. Upon decompression, the high-pressure phase of BaSO4 transforms back into its initial structure, which indicates a reversible phase transition. However, no phase transitions have been detected in SrSO4 over the experimental P–T range. In addition, fitting a third-order Birch–Murnaghan equation of state to the pressure–volume data yields the bulk moduli and their pressure derivatives of BaSO4 and SrSO4. Simultaneously, the thermal expansion coefficients of BaSO4 and SrSO4 are also obtained, by fitting the temperature-volume data to the Fei-type thermal equation of state. Furthermore, the compositional effects on the phase transformation and thermoelastic behavior of barite-group minerals are also discussed, and the results suggest that the bond length of < M–O > (M=Ba, Sr, Pb) is an important factor that causes the phase transition pressure of SrSO4 to be the largest, PbSO4 is the second, and BaSO4 is the lowest. [ABSTRACT FROM AUTHOR]

The compressibility and expansivity of anglesite (PbSO4) have been measured at high pressure up to 21.6 GPa and high temperature up to 700 K using in situ angle-dispersive X-ray diffraction and diamond anvil cell. The third-order Birch-Murnaghan equation of state (III-BM-EoS) was used to analyze the pressure-volume (P-V) data of PbSO4. We obtained the bulk modulus K0 = 59(1) GPa, and its pressure derivative K0′ = 5.3(4), respectively. Using Holland-Powell thermal EoS to fit the temperature-volume (T-V) data, the thermal expansion coefficient α0 = 4.59(2) × 10− 5 K− 1 for PbSO4 was also derived. Simultaneously, the ambient-pressure axial compressibilities (βa0 = 1.79(4) × 10− 3 GPa− 1, βb0 = 1.75(5) × 10− 3 GPa− 1, βc0 = 2.12(4) × 10− 3 GPa− 1) and axial thermal expansivities (αa0 = 1.23(4) × 10− 5 K− 1, αb0 = 1.93(2) × 10− 5 K− 1, and αc0 = 1.43(1) × 10− 5 K− 1) along a-axis, b-axis and c-axis were derived at 300 K, respectively. Furthermore, the potential influencing factors (e.g., the effective size of M2+ cation, polarizability and electronegativity) on the bulk moduli of barite-type (belonging to Pbnm space group) sulfates (anglesite, barite, and celestine) were discussed. We found that the polarizability might be the most important factor. Finally, the anisotropic linear compressibility and thermal expansivity in barite-type sulfates were also discussed, respectively. [ABSTRACT FROM AUTHOR]

The equation of state and stability of topaz at high-pressure/high-temperature conditions have been investigated by in situ synchrotron X-ray diffraction (XRD) and Raman spectroscopy in this study. No phase transition occurs on topaz over the experimental pressure–temperature (P-T) range. The pressure–volume data were fitted by the third-order Birch–Murnaghan equation of state (EoS) with the zero-pressure unit–cell volume V0 = 343.86 (9) Å3, the zero-pressure bulk modulus K0 = 172 (3) GPa, and its pressure derivative K'0 = 1.3 (4), while the obtained K0 = 155 (2) GPa when fixed K'0 = 4. In the pressure range of 0–24.4 GPa, the vibration modes of in-plane bending OH-groups for topaz show non-linear changes with the increase in pressure, while the other vibration modes show linear changes. Moreover, the temperature–volume data were fitted by Fei's thermal equation with the thermal expansion coefficient α300 = 1.9 (1) × 10−5 K−1 at 300 K. Finally, the P-T stability of topaz was studied by a synchrotron-based single-crystal XRD at simultaneously high P-T conditions up to ~10.9 GPa and 700 K, which shows that topaz may maintain a metastable state at depths above 370 km in the upper mantle along the coldest subducting slab geotherm. Thus, topaz may be a potential volatile-carrier in the cold subduction zone. It can carry hydrogen and fluorine elements into the deep upper mantle and further affect the geochemical behavior of the upper mantle. [ABSTRACT FROM AUTHOR]

Crystal-chemical properties of synthetic Almandine-Pyrope (Alm-Pyr) solid solutions were investigated by X-ray single-crystal diffraction and Raman spectroscopy. Garnet solid solution with different compositions were synthesized from powder at 4.0 GPa and annealed at 1200 °C for 48 h by a multi-anvil pressure apparatus. Garnet crystals with different sizes (about 60–1000 μm) were obtained from synthesis. The results of X-ray single-crystal diffraction show that the unit cell constants decrease with increasing Pyr contents in the synthetic Alm-Pyr crystals due to the smaller ionic radius of Mg2+ in eightfold coordination than that of Fe2+. The data exhibit obviously positive deviations from ideal mixing volumes across the Alm-Pyr join which may be caused by the distortion of the SiO4 tetrahedron. Moreover, the significant decrease in the average M-O bond length and volume of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell constant and volume. On the other hand, selected bond distances (average , , and distances) have a linear correlation with the unit-cell parameter, but the distance has nonlinear correlation. With increasing the unit-cell parameter, the average distance increases significantly, followed by the average and distances. While the distance changes negligibly further confirming the conclusion that the significant decrease of the average M-O bond length of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell volume. In the Raman spectra collected for the Alm-Pyr solid solutions, Raman vibration mode assignments indicate that the Raman vibrational spectra change along the Alm-Pyr binary solution. The mode frequencies of Si-O stretching, Si-O bending, and the rotation of the SiO4-tetrahedron (R(SiO4)) decrease linearly, while the translational modes of the SiO4-tetrahedron (T(SiO4)) increase with increasing Alm contents. [ABSTRACT FROM AUTHOR]

The high-temperature unit-cell parameters and volumes of three Li-bearing tourmalines (elbaite (CC05), elbaite (CC11) and schorl (D54)) have been determined through in situ synchrotron radiation angle-dispersive X-ray diffraction experiments. No phase transition of these tourmalines has been observed up to the maximum temperature in this study. The volumetric thermal expansion coefficients of the three Li-bearing tourmalines are determined from the measured unit-cell volumes at high temperatures with Berman's equations. And the elbaite (CC05) has the least volumetric thermal expansion coefficients among the three Li-bearing tourmalines in this study. Furthermore, the axial thermal expansion behavior of these Li-bearing tourmalines is also fitted with "linearized" Berman's equation. The results show that Li-bearing tourmalines has an intense anisotropic axial thermal expansivity, where the c -axis has a larger axial thermal expansion coefficient than a -axis. The potential factors influencing on the thermal expansivity and the anisotropic axial thermal expansivities of Li-bearing tourmalines are further discussed. • Temperature dependence of the unit-cell parameters of Li-bearing tourmalines, established using synchrotron-based XRD. • No phase transition of these tourmalines has been observed up to the maximum temperature in this study. • Li-bearing tourmaline has an intense anisotropic axial thermal expansivity. • The different compositions at Y site may affect the volumetric thermal expansion coefficients of Li-bearing tourmalines. [ABSTRACT FROM AUTHOR]