A High-Pressure Investigation of the Synthetic Analogue of Chalcomenite, CuSeO3∙2H2O

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

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.

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

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.