Nature Research Acta Medica Okayama 2041-1723 12 1 2021 Ultrafast olivine-ringwoodite transformation during shock compression 4305 EN Takuo Okuchi Institute for Integrated Radiation and Nuclear Science, Kyoto University Yusuke Seto Graduate School of Science, Kobe University Naotaka Tomioka Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) Takeshi Matsuoka Institute for Open and Transdisciplinary Research Initiatives, Osaka University Bruno Albertazzi Graduate School of Engineering, Osaka University Nicholas J. Hartley Graduate School of Engineering, Osaka University Yuichi Inubushi Japan Synchrotron Radiation Research Institute, Kento Katagiri Graduate School of Engineering, Osaka University Ryosuke Kodama Graduate School of Engineering, Osaka University Tatiana A. Pikuz Graduate School of Engineering, Osaka University Narangoo Purevjav Institute for Planetary Materials, Okayama University Kohei Miyanishi RIKEN SPring-8 Center Tomoko Sato Graduate School of Science, Hiroshima University Toshimori Sekine Graduate School of Engineering, Osaka University Keiichi Sueda RIKEN SPring-8 Center Kazuo A. Tanaka Graduate School of Engineering, Osaka University Yoshinori Tange Japan Synchrotron Radiation Research Institute Tadashi Togashi Japan Synchrotron Radiation Research Institute Yuhei Umeda Institute for Integrated Radiation and Nuclear Science, Kyoto University Toshinori Yabuuchi Japan Synchrotron Radiation Research Institute Makina Yabashi Japan Synchrotron Radiation Research Institute Norimasa Ozaki Graduate School of Engineering, Osaka University Meteorites from interplanetary space often include high-pressure polymorphs of their constituent minerals, which provide records of past hypervelocity collisions. These collisions were expected to occur between kilometre-sized asteroids, generating transient high-pressure states lasting for several seconds to facilitate mineral transformations across the relevant phase boundaries. However, their mechanisms in such a short timescale were never experimentally evaluated and remained speculative. Here, we show a nanosecond transformation mechanism yielding ringwoodite, which is the most typical high-pressure mineral in meteorites. An olivine crystal was shock-compressed by a focused high-power laser pulse, and the transformation was time-resolved by femtosecond diffractometry using an X-ray free electron laser. Our results show the formation of ringwoodite through a faster, diffusionless process, suggesting that ringwoodite can form from collisions between much smaller bodies, such as metre to submetre-sized asteroids, at common relative velocities. Even nominally unshocked meteorites could therefore contain signatures of high-pressure states from past collisions. No potential conflict of interest relevant to this article was reported.

International Union of Crystallography Acta Medica Okayama 2052-2525 7 3 2020 Strong hydrogen bonding in a dense hydrous magnesium silicate discovered by neutron Laue diffraction 370 374 EN Narangoo Purevjav Institute for Planetary Materials, Okayama University Takuo Okuchi Institute for Planetary Materials, Okayama University Christina Hoffman Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory A large amount of hydrogen circulates inside the Earth, which affects the long-term evolution of the planet. The majority of this hydrogen is stored in deep Earth within the crystal structures of dense minerals that are thermodynamically stable at high pressures and temperatures. To understand the reason for their stability under such extreme conditions, the chemical bonding geometry and cation exchange mechanism for including hydrogen were analyzed in a representative structure of such minerals (i.e. phase E of dense hydrous magnesium silicate) by using time-of-flight single-crystal neutron Laue diffraction. Phase E has a layered structure belonging to the space group R (3) over barm and a very large hydrogen capacity (up to 18% H2O weight fraction). It is stable at pressures of 13-18 GPa and temperatures of up to at least 1573 K. Deuterated high-quality crystals with the chemical formula Mg2.28Si1.32D2.15O6 were synthesized under the relevant high-pressure and high-temperature conditions. The nuclear density distribution obtained by neutron diffraction indicated that the O-D dipoles were directed towards neighboring O2- ions to form strong interlayer hydrogen bonds. This bonding plays a crucial role in stabilizing hydrogen within the mineral structure under such high-pressure and high-temperature conditions. It is considered that cation exchange occurs among Mg2+, D+ and Si4+ within this structure, making the hydrogen capacity flexible. No potential conflict of interest relevant to this article was reported.