Kazuki Komatsu 교수

The single-crystal synchrotron study of the high-pressure modification of aluminium oxide hydroxide, δ-AlOOH, confirms the previous structure determination in the space group P21nm, which was based on X-ray powder data [Suzuki, Ohtani & Kamada (2000). Phys. Chem. Miner. 27, 689–693]. The present study includes the determination of the H-atom parameters, which revealed a strong asymmetric hydrogen bond with an O⋯O distance of 2.5479 (12) Å. The δ-AlOOH structure is isotypic with that of β-CrOOH a

Most ice polymorphs have order-disorder "pairs" in terms of hydrogen positions, which contributes to the rich variety of ice polymorphs; in fact, three recently discovered polymorphs- ices XIII, XIV, and XV-are ordered counter forms to already identified disordered phases. Despite the considerable effort to understand order-disorder transition in ice crystals, there is an inconsistency among the various experiments and calculations for ice XV, the ordered counter form of ice VI, i.e., neutron di

We developed a new device involving an individual P–T controlling system for neutron-scattering experiments available at 0–10 GPa and at 77–473 K. Thanks to the thermal insulators made of zirconia and glass-fiber-reinforced plastic under the anvils, temperature only around anvils can be controllable with fast heating/cooling rate of<20 K/min, and it also allows us to use normal hydraulic oil even at low temperatures, which has much less risk of leaking compared with helium gas. The feasibility t

Above 2 GPa the phase diagram of water simplifies considerably and exhibits only two solid phases up to 60 GPa, ice VII and ice VIII. The two phases are related to each other by hydrogen ordering, with the oxygen sublattice being essentially the same. Here we present neutron diffraction data to 15 GPa which reveal that the rate of hydrogen ordering at the ice VII-VIII transition decreases strongly with pressure to reach timescales of minutes at 10 GPa. Surprisingly, the ordering process becomes

The current epoch can be described as the ‘age of ice-rush’, as the rate of discovery of ice polymorphs, of which there are currently 20 known, has accelerated, particularly since the end of the last century. This is largely owing to advances in neutron diffraction under pressure. Neutrons can interact with light elements such as hydrogen as well as heavy elements, making neutron diffraction essential for full structural analyses of newly discovered ice polymorphs. It is especially useful for de

Magnesium dichloride decahydrate (MgCl2·10H2O) and its deuterated counterpart (MgCl2·10D2O) are identified for the first time by in-situ powder synchrotron X-ray and spallation neutron diffraction. These substances are crystallized from a previously unidentified nanocrystalline compound, which originates from an amorphous state at low temperature. A combination of a recently developed autoindexing procedure and the charge-flipping method reveals that the crystal structure of MgCl2·10H2O consists

Hydrogen bond symmetrisation is the phenomenon where a hydrogen atom is located at the centre of a hydrogen bond. Theoretical studies predict that hydrogen bonds in ice VII eventually undergo symmetrisation upon increasing pressure, involving nuclear quantum effect with significant isotope effect and drastic changes in the elastic properties through several intermediate states with varying hydrogen distribution. Despite numerous experimental studies conducted, the location of hydrogen and hence

The effect of temperature and pressure was analyzed on the crystal structure of natural topaz from Gilgit division, Pakistan. The unit cell parameters at 298K, 423K, 573K, 723K, 873K, 1023K and 1173K, and X-ray diffraction intensity data at 298K, 573K, 873K and 1173K were collected using an imaging plate X-ray diffractometer equipped with rotating anode generator. Thermal expansion coefficients along the unit cell edges and of the volume are αa=6.4(7)×10-6K-1, αb=5.5(6) ×10-6K-1, αc=8.1(6) ×10-6

OH stretching vibration modes for F-rich natural topaz (F-topaz) and for fully hydrated topaz (topaz-OH) synthesized at high pressure, were observed using IR and Raman spectroscopies at pressures up to 30.4 GPa and 17.3 GPa, respectively. In F-topaz, the pressure derivative of the frequency of the OH stretching band observed at 3650 cm-1 at ambient pressure was 0.91(3) cm-1/GPa, which was consistent with the value recently reported by Bradbury and Williams (2003). On the other hand, in topaz-OH,

The high-pressure phase of gibbsite has been studied by in situ single crystal X-ray diffraction method and molecular dynamics (MD) simulation at 3.0 GPa. The crystal structure of the high-pressure phase, η -Al(OH) 3 , was successfully determined by direct methods based on the intensities of X-ray diffraction. The space group and lattice constants for η -Al(OH) 3 are P 2 1 / b 11 (#14), a = 8.612(3) Å, b = 5.013(2) Å, c = 9.194(5) Å and α = 90.34(6)°, respectively. The crystal structure of η -Al

A new high pressure cell for neutron diffraction experiments using nano-polycrystalline anvils is presented. The cell design, off-line pressure generation tests and a gas-loading procedure for this cell are described. The performance is illustrated by powder neutron diffraction patterns of ice VII to ∼82 GPa. We also demonstrate the feasibility of single crystal neutron diffraction experiments of Fe3O4 at ambient conditions using this cell and discuss the current limitation and future developmen

Three kinds of ceramics, zirconia-toughened alumina (ZTA), alumina-toughened zirconia (ATZ) and yttria-stabilized zirconia (YSZ), were tested as anvil materials, mainly for the purpose of neutron scattering study under high pressure. ZTA with non-toroidal anvil profile, having the same sample volume as conventionally used double toroidal anvils, sustained pressures up to 11.9 GPa. This is comparable to anvils made of tungsten carbide (TC) with Ni binder with the same dimensions. ATZ would also b