Hydrogen site analyses of dense hydrous mantle minerals by pulsed neutron powder diffraction

Deuterium site positions and occupancies in the crystal structures of synthetic hydrous ringwoodite [γ-(Mg_1.72 Fe_0.17D_0.22)(Si_0.97D_0.12)O₄] and dense hydrous magnesium silicate (DHMS) phase E [Mg_2.28Si_1.31O₆D_2.22] have been determined for the first time by high-resolution time-of-flight (TOF) neutron powder diffraction conducted at Japan Proton Accelerator Research Complex (J-PARC). These two minerals are the promised major careers of deep-mantle water. They were synthesized at pressures up to 19 GPa and at temperatures up to 1300°C using a Kawai-type apparatus, for which we have newly designed two types of furnace assemblies to uniformly heat large masses of samples at these pressures (45 to 80 mg for each experimental run). The products were chemically uniform and free from any contamination of ¹H. We successfully refined the structures of the two minerals to find the relations between their chemical bonding states and their physical properties.