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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 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]