SHELXT is a revolutionary program which solves the structure assuming space group P1, and determines the space group type based on the assigned Laue group and calculated P1 phase angles. The background and procedures of the computation will be summarized, and important points to check the results will be noted.
Here I discuss a problem of an inconsistency among various experiments and calculations for ice XV, the ordered form of ice VI, i.e., neutron diffraction observations suggest antiferroelectrically ordered structures, which disagree with dielectric measurement and theoretical studies, implying ferroelectrically ordered structures. Our recent neutron diffraction experiments and DFT calculations support a scenario in which several kinds of ordered configuration coexist, which was proposed more than 40 years ago by Kamb. More recently published arguments in terms of this issue are also briefly reviewed.
PLANET is a powder neutron diffractometer dedicated to high-pressure experiments. By combining the intense neutron source of J-PARC and the high-pressure devices designed for time-of-flight powder neutron diffraction, precise structure analysis of crystal, liquid, and amorphous solids is possible over wide pressure and temperature range of 0～20 GPa and 77～2,000 K. This beamline is effective for various studies in geophysics, planetary science, physics and chemistry. This paper overviews the beamline and introduces recent results obtained at PLANET.
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.