A High-pressure Investigation of the Synthetic Analogue of Chalcomenite, CuSeO&lt;sub&gt;3&lt;/sub&gt;∙2H&lt;sub&gt;2&lt;/sub&gt;O

The phase stability of epsomite under a high temperature and high pressure were explored through Raman spectroscopy and electrical conductivity measurements in a diamond anvil cell up to ~623 K and ~12.8 GPa. Our results verified that the epsomite underwent a pressure-induced phase transition at ~5.1 GPa and room temperature, which was well characterized by the change in the pressure dependence of Raman vibrational modes and electrical conductivity. The dehydration process of the epsomite under high pressure was monitored by the variation in the sulfate tetrahedra and hydroxyl modes. At a representative pressure point of ~1.3 GPa, it was found the epsomite (MgSO4·7H2O) started to dehydrate at ~343 K, by forming hexahydrite (MgSO4·6H2O), and then further transformed into magnesium sulfate trihydrate (MgSO4·3H2O) and anhydrous magnesium sulfate (MgSO4) at higher temperatures of 373 and 473 K, respectively. Furthermore, the established P-T phase diagram revealed a positive relationship between the dehydration temperature and the pressure for epsomite.

The Phase Transition and Dehydration in Epsomite under High Temperature and High Pressure

Yang

Dai

et al. 2020

A Short Review of Current Computational Concepts for High-Pressure Phase Transition Studies in Molecular Crystals

Rychkov

2020

High-pressure chemistry of organic compounds is a hot topic of modern chemistry. In this work, basic computational concepts for high-pressure phase transition studies in molecular crystals are described, showing their advantages and disadvantages. The interconnection of experimental and computational methods is highlighted, showing the importance of energy calculations in this field. Based on our deep understanding of methods’ limitations, we suggested the most convenient scheme for the computational study of high-pressure crystal structure changes. Finally, challenges and possible ways for progress in high-pressure phase transitions research of organic compounds are briefly discussed.

Investigation of the High-Pressure Behaviors of Amblygonite by Single-Crystal X-ray Diffraction, Raman Spectroscopy, and DFT Calculations

Qin,

Hou,

et al. 2023

In the present study, we extensively explored the high-pressure behaviors and vibrational properties of amblygonite LiAlPO4F with elevated pressures up to 34.3 GPa based on single-crystal X-ray diffraction measurements, Raman spectroscopy, and DFT calculations. The compressibility and elastic properties of amblygonite were determined first. Specifically, the obtained isothermal bulk modulus of LiAlPO4F is 128(4) GPa and the triclinic phase exhibited anisotropic compression with axial compressibility βc > βa > βb with a ratio of 1.11:1.00:1.20. The Raman spectra showed no indication of phase transformation and were used to obtained mode Grüneisen parameters. The average Grüneisen parameter for PO4 tetrahedral sites was smaller than for the LiO4F sites. Our results provide new insights into the phase stability and elastic properties of lithium-fluorite granites at extreme conditions.