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Yamashita, Keishiro*; Komatsu, Kazuki*; Klotz, S.*; Fabelo, O.*; Fern
ndez-D
az, M. T.*; Abe, Jun*; Machida, Shinichi*; Hattori, Takanori; Irifune, Tetsuo*; Shimmei, Toru*; et al.
Proceedings of the National Academy of Sciences of the United States of America, 119(40), p.e2208717119_1 - e2208717119_6, 2022/10
Times Cited Count：2 Percentile：22.35(Multidisciplinary Sciences)Here we present the first elucidation of the disordered structure of ice VII, the dominant high-pressure form of water, at 2.2 GPa and 298 K from both single-crystal and powder neutron diffraction techniques. We reveal the three-dimensional atomic distributions from the maximum entropy method and unexpectedly find a ring-like distribution of hydrogen in contrast to the commonly-accepted discrete sites. In addition, total scattering analysis at 274 K clarified the difference in the intermolecular structure from ice VIII, the ordered counterpart of ice VII, despite an identical molecular geometry. Our complementary structure analyses robustly demonstrate the unique disordered structure of ice VII. Furthermore, these noble findings are related to the proton dynamics which drastically vary with pressure, and will contribute to an understanding of the structural origin of anomalous physical properties of ice VII under pressures.
Klotz, S.*; Baptiste, B.*; Hattori, Takanori; Feng, S. M.*; Jin, Ch.*; B
neut, K.*; Guigner, J. M.*; Est
ve, I.*
Carbon, 185, p.491 - 500, 2021/11
Times Cited Count：1 Percentile：6.33(Chemistry, Physical)Carbon disulphide (CS) is one of the simplest molecular systems made of double covalent bonds. Under high pressure, the molecular structure is expected to break up to form extended crystalline or polymeric solids. Here we show that by compression at 300 K to approximately 
10 GPa using large-volume high pressure techniques, an instantaneous reaction leads to a mixture of pure sulphur and a well-defined compound with stoichiometry close to CS which can be recovered to ambient pressure. We present neutron and X-ray diffraction as well as Raman data which show that this material consists of sulphur bonded to sp
graphite layers of nanometric dimensions. The compound is a semiconductor with a gap of 45 meV, as revealed by temperature dependent resistivity measurements, and annealing at temperatures above 200
C allow to reduce its sulphur content up to C
S. Its structural and electronic properties are fundamentally different to "Bridgman black" reported from previous high pressure experiments on CS.
Komatsu, Kazuki*; Klotz, S.*; Machida, Shinichi*; Sano, Asami; Hattori, Takanori; Kagi, Hiroyuki*
Proceedings of the National Academy of Sciences of the United States of America, 117(12), p.6356 - 6361, 2020/03
Times Cited Count：16 Percentile：57.81(Multidisciplinary Sciences)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 sub-lattice 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 time scales of minutes at 10 GPa. Surprisingly, the ordering process becomes more rapid again upon further compression. We show that such an unusual change in transition rate can be explained by a slowing-down of the rotational dynamics of water molecules with a simultaneous increase of translational motion of hydrogen under pressure, as previously suspected. The observed crossover in the hydrogen dynamics in ice is likely the origin of various hitherto unexplained anomalies of ice VII in the 10-15 GPa range reported by Raman spectroscopy, X-ray diffraction, and proton conductivity.
Komatsu, Kazuki*; Klotz, S.*; Nakano, Satoshi*; Machida, Shinichi*; Hattori, Takanori; Sano, Asami; Yamashita, Keishiro*; Irifune, Tetsuo*
High Pressure Research, 40(1), p.184 - 193, 2020/02
Times Cited Count：13 Percentile：72.32(Physics, Multidisciplinary)A new high pressure cells for neutron diffraction experiments using nano-polycrystalline anvil 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 Fe
O
at ambient conditions using this cell and discuss the current limitation and future developments.
Klotz, S.*; Komatsu, Kazuki*; Polian, A.*; Machida, Shinichi*; Sano, Asami; Iti, J.-P.*; Hattori, Takanori
Physical Review B, 101(6), p.064105_1 - 064105_6, 2020/02
Times Cited Count：4 Percentile：26.53(Materials Science, Multidisciplinary)Manganese oxide (MnO) is a prototype of an antiferromagnetic Mott-insulator. Here we investigate the interplay of magnetic ordering and lattice distortion across the Nel temperature 
under pressure using neutron and X-ray diffraction. We find an increase of with a rate of 
= +4.5(5) K/GPa, an increase of the rhombohedral distortion 
by 
= +0.018/GPa, as well as a volume striction which is insensitive to pressure. These results allow to retrieve the dependence of the coupling constants 
and 
on interatomic distances and compare it to first-principles predictions. Antiferromagnetic diffuse scattering was observed up to 1.2 , and long-range magnetic order appears at room temperature at 42 GPa.
to 34 GPaKlotz, S.*; Casula, M.*; Komatsu, Kazuki*; Machida, Shinichi*; Hattori, Takanori
Physical Review B, 100(2), p.020101_1 - 020101_5, 2019/07
Times Cited Count：11 Percentile：53.18(Materials Science, Multidisciplinary)Ytterbium dihydride (YbH) shows a well-known transition at 
16 GPa from a CaH-type structure to a high-pressure (high-
) phase with Yb at hcp sites and unknown H-positions. Here, we report its complete structure determination by neutron diffraction at 34 GPa. Hydrogen(deuterium) is located at 2
and 2
positions of space group 
, thus forming a high-symmetry "collapsed" close-packed lattice. The transition is sluggish and can be seen as a transfer of 1/2 of the hydrogen atoms from strongly corrugated H-layers to interstitial sites of the Yb-lattice. We demonstrate by first-principles calculations that the transition is related to a change from a completely filled 
-electron configuration to a fractional -hole (0.25 h) occupation in the high- phase. The 
charge transfer closes the gap at the transition and leads to a metallic ground state with sizeable electron-phonon interaction involving out-of-plane vibrational modes of interstitial hydrogen.
Klotz, S.*; Komatsu, Kazuki*; Kagi, Hiroyuki*; Kunc, K.*; Sano, Asami; Machida, Shinichi*; Hattori, Takanori
Physical Review B, 95(17), p.174111_1 - 174111_7, 2017/05
Times Cited Count：35 Percentile：81.61(Materials Science, Multidisciplinary)The compression behaviour of deuterated ice VII and VIII was investigated by high pressure neutron scattering in the pressure range 2-13.7 GPa between 93 K and 300 K. We establish equations-of-state which contain accurate values for the bulk moduli B
, their pressure derivatives B', as well as the ambient pressure volumina V. These equations-of-state hold over a large part of the stability domain of ice VII, by comparison with available X-ray data, and to at least 
13 GPa for ice VIII. They are indistinguishable at low pressures, but beyond 7 GPa and at low temperatures ice VIII appears to become stiffer than expected. This might be related to an anomalous phonon hardening observed previously in ice VIII in this 
range [D.D. Klug et al., Physical Review B, 70, 144113 (2004)].
Klotz, S.*; Komatsu, Kazuki*; Pietrucci, F.*; Kagi, Hiroyuki*; Ludl, A.-A.*; Machida, Shinichi*; Hattori, Takanori; Sano, Asami; Bove, L. E.*
Scientific Reports (Internet), 6, p.32040_1 - 32040_8, 2016/08
Times Cited Count：27 Percentile：60.26(Multidisciplinary Sciences)It has been known since decades that certain aqueous salt solutions of LiCl and LiBr readily form glasses when cooled to below 160 K. This fact has recently been exploited to produce a 
salty
high pressure ice form: When the glass is compressed at low temperatures to pressures higher than 4 GPa and subsequently warmed, it crystallizes into ice VII with the ionic species trapped inside the ice lattice. Here we report the extreme limit of salt incorporation into ice VII, using high pressure neutron diffraction and molecular dynamics simulations. We show that high-pressure crystallization of aqueous solutions of LiCl
5.6HO and LiBr5.6HO leads to solids with strongly expanded volume, a destruction of the hydrogen-bond network with an isotropic distribution of water-dipole moments, as well as a crystal to-amorphous transition on decompression. This highly unusual behavior constitutes an interesting pathway from a glass to a crystal where translational periodicity is restored but the rotational degree of freedoms remaining completely random.
Kitazawa, Sin-iti; Okayama, Katsumi*; Neyatani, Yuzuru; Sagot, F.*; Van Houtte, D.*; Abadie, L.*; Yonekawa, Izuru*; Wallander, A.*; Klotz, W.-D.*
Fusion Engineering and Design, 87(7-8), p.1510 - 1513, 2012/08
Times Cited Count：8 Percentile：52.49(Nuclear Science & Technology)In the ITER project, Reliability, Availability, Maintainability and Inspectability (RAMI) approach has been adopted for technical risk control to guide the design of components and the preparation for operation and maintenance. RAMI analysis of the ITER CODAC system, the central plant control system, was performed in the current design available in conceptual design phase. A functional breakdown was prepared in a bottom-up approach, resulting in the system being divided into 5 main functions and sub-functions. Criticality matrices highlight the risks of the different failure modes with regard to their probability of occurrence and the impact on the availability. Reliability block diagrams were prepared to estimate the reliability and availability of each function under operating conditions. The inherent availability of the mandatory functions for the control of plasma experiments with mitigations was calculated to be 99.2% that is higher than the project required value of 98.8%.
