Date: 16:00 – 18:00, Friday, November, 4, 2022
Speaker: Xuejing He
Title: High-pressure studies of variscite using X-ray diffraction and FTIR spectroscopy
Variscite (ideal formula: AlPO4·2H2O) is a hydrated mineral crystallizes in an orthorhombic structure (Pbca, Z = 8), comprising corner-sharing [AlO6] octahedra and [PO4] tetrahedral. In the crystal structure of variscite, the bound water molecules form four types of hydroxyls. Under ambient conditions, three of the four O-H dipoles form hydrogen bonds with neighboring oxygen atoms, i.e., OW1-H11⋯O1, OW2-H21⋯O2, and OW2-H22⋯O4, while the hydroxyl of OW1-H12 is nearly free of hydrogen-bonding interaction because of the rather longer interatomic distance between OW1 and O3 (Kniep et al. 1977).
Variscite (Pbca, Z = 8) has a series of polymorphs and analogues, i.e., AlPO4 and AlPO4·xH2O, which have been widely investigated under high pressure and high temperature. Investigating the crystallography of variscite (Pbca, Z = 8) under high pressure and high temperature would help to enrich the knowledge of these series of compounds. In this study, we have performed in-situ high-pressure XRD and mid-infrared spectroscopic experiments to study the pressure-induced modification of the crystal structure and the hydrogen-bonding configuration of variscite.