Quantitative Analysis of Hydrogen Site and Occupancy in a Deep-Earth Hydrous Mineral by Time-of-Flight Single Crystal Laue Neutron Diffraction

Abstract

Water in the Earth has been transported from the oceans into its deep interior, where it forms hydrous deep mantle minerals. Wadsleyite ［（Mg,Fe）₂SiO₄］ has been considered as one of the most important host minerals incorporating this type of water as hydroxyl groups. To constrain the capacity of water in its structure and also to understand the effect of such water on its physical properties, it is essential to quantitatively determine the hydrogenʼs site and occupancy in the wadsleyite structure. Here we conduct a neutron time-of-flight single-crystal Laue diffraction study of it. Single crystals, which have size and quality suitable for this method, were successfully synthesized by a slow-cooling method at the relevant high pressure and temperature condition. The results unambiguously demonstrate a unique incorporation mechanism of hydrogen into the wadsleyite structure.