Energy-dispersive X-ray diffraction study of liquid gallium under high pressure at elevated temperatures

Yagafarov, O.; Katayama, Yoshinori; Brazhkin, V. V.*; Lyapin, A. G.*; Saito, Hiroyuki

High Pressure Research, 33(1), p.191 - 195, 2013/01

https://doi.org/10.1080/08957959.2012.757311

Densified low-hygroscopic form of PO glass

Brazhkin, V. V.*; Akola, J.*; Katayama, Yoshinori; Kohara, Shinji*; Kondrin, M. V.*; Lyapin, A. G.*; Lyapin, S. G.*; Tricot, G.*; Yagafarov, O.

Journal of Materials Chemistry, 21(28), p.10442 - 10447, 2011/07

https://doi.org/10.1039/c1jm10889a

PO compound is an archetypical glass-forming oxide with a high hygroscopicity. We found that the quenching from the POmelt under ultrahigh pressures enables obtaining densified PO glasses with a residual densification up to 12% at normal conditions. These glasses have a low hygroscopicity and can exist under air conditions for several weeks. An examination of the structure of the new form of PO glass reveals a cardinal decrease of the volume of nanovoids in the glassy matrix.

Neutron scattering experiment on water under high pressure and temperature

Katayama, Yoshinori; Yagafarov, O.; Hattori, Takanori

no journal, , 

We plan to carry out neutron scattering experiments on liquid water under high pressure and temperature using a high pressure neutron diffractometer, PLANET, which will be available in fall this year, at J-PARC. Our previous synchrotron X-ray diffraction experiments and molecular dynamics simulation studies have revealed that structure of liquid water changes drastically under high pressure and temperature. But experimental observation of hydrogen is limited and neutron experiments are necessary to understand pressure and temperature dependence of hydrogen bonds in water. In this presentation, scientific background and the present status of target, design of an high-pressure assembly, methods for data analysis will be shown.

Densified SiO glass study by RMC simulation using X-ray and neutron diffraction data

Yagafarov, O.; Kohara, Shinji*; Temleitner, L.*; Inamura, Yasuhiro; Katayama, Yoshinori

no journal, , 

Structure of water under high pressure and high temperature

Katayama, Yoshinori; Yagafarov, O.; Ikeda, Takashi; Saito, Hiroyuki; Aoki, Katsutoshi; Hattori, Takanori; Fukui, Hiroshi*; Tange, Yoshinori*; Funakoshi, Kenichi*

no journal, , 

Liquid water at ambient pressure shows unique properties and they are related to the network structure formed by hydrogen bonds between water molecules. To study structural change in the liquid water under high-pressure and high-temperature conditions, we have measured X-ray diffraction of liquid water just above the melting line up to 20 GPa. Up to 4 GPa, the coordination number increased rapidly while the intermolecular distance changed slightly. First-principles molecular dynamics simulations were also performed for high-density water. Results of the simulations in a wide pressure- temperature range revealed that temperature was more important factor for the crossover between the hydrogen-bonded and simple liquid-like liquids. We have measured X-ray diffraction of water as a function of temperature. The experimental results supported the results of the simulation.

Feasibility study of neutron diffraction measurements of silica glass under high pressure

Katayama, Yoshinori; Yagafarov, O.; Machida, Akihiko; Hattori, Takanori; Sano, Asami; Komatsu, Kazuki*; Otomo, Toshiya*

no journal, , 

To test feasibility of neutron diffraction measurements of glass at high pressures up to several GPa, a sample of silica glass in a Paris-Edinburgh type high-pressure apparatus was measured at ambient conditions using a total scattering spectrometer, NOVA, at the Japan Proton Accelerator Complex (J-PARC). The sample has a shape of double convex lens, 6 mm in diameter, 4.4 mm in thickness. It was surrounded by a ring-shape gasket made of TiZr alloy and two anviles made of tungsten carbide. The incident neutron beam passed through a anvil and the diffracted beam passed through the gasket. The data acquisition time was about 20 hours. A vanadium sample and the empty gasket were also measured as references. A clear oscillation was observed in the intensity as a function of wave number.

Measurements of silica glass and water using a high-prssure diffractometer in J-PARC/MLF

Katayama, Yoshinori; Hattori, Takanori; Yagafarov, O.*; Saito, Hiroyuki; Sano, Asami; Suzuya, Kentaro; Chiba, Ayano*

no journal, , 

As the first high-pressure experiments on structurally disordered materials using a new high-pressure neutron diffractometer, PLANET, installed in J-PARC/MLF, measurements of silica glass were caried out. We compressed a sample in a ZrO cube using a six-axis press and measured diffraction at pressures of 0.1 MPa, 2.3, 5.5, 7.5 and 9.9 GPa at room temperature. The size of the sample was 4.6 mm in diameter and 6.7 mm in height. The size of the incident beam was 2.5 mm in width and 4.5 mm in height. The pressure was estimated from the applied load. Vanadium sample and empty cell were also measured for the correction of the diffraction intensity. Clean diffraction patterns without diffraction lines from surrounding materials were obtained thanks to the radial collimator system. Measurements on heavy water at room temperature, 100C and 200C at 0.8 GPa were also carried out. Significant temperature dependence of diffraction pattern was observed.

High-pressure neutron experiments on SiO glass using J-PARC high-pressure neutron diffractometer PLANET

Hattori, Takanori; Yagafarov, O.*; Katayama, Yoshinori; Sano, Asami; Saito, Hiroyuki; Chiba, Ayano*; Inamura, Yasuhiro; Suzuya, Kentaro; Otomo, Toshiya*

no journal, , 

SiO glass consists of SiO tetrahedra. This glass is easily densified by applying pressure, due to its relatively sparse network ring formed by the linkage of tetrahedra. The density increase amounts to 20% by room temperature compression to 8 GPa. This increase is, however, released after decompression because of insufficient structural relaxation. On the other hand, the heating at high pressures promotes the structural relaxation, resulting in permanent densification of 20% at most. The mechanism of this densification has been investigated so far, but the microscopic origin is still to be revealed. So, we performed in-situ high-pressure neutron experiments at newly constructed high-pressure neutron beamline PLANET in J-PARC. We will discuss the origin of the reversibility in the densification.

X-ray and neutron structural study on water under high pressure and high temperature

Katayama, Yoshinori; Hattori, Takanori; Saito, Hiroyuki; Sano, Asami; Suzuya, Kentaro; Yagafarov, O.*; Chiba, Ayano*; Otomo, Toshiya*

no journal, , 

Liquid water at ambient conditions has an ice-like, characteristic structure due to the hydrogen bonds between molecules. To study pressure and temperature dependence of the structure of water, we have carried out in-situ high-temperature high-pressure measurements on liquid water using synchrotron radiation at the SPring-8 and molecular dynamics simulations. The results revealed transformation from the ice-like structure to a simple-liquid-like structure. To investigate change in hydrogen bonds, neutron is an important probe. We carried out neutron diffraction measurements on heavy water at room temperature, 100C and 200C at 0.8 GPa using newly-built high-pressure diffractometer, PLANET, at J-PARC/MLF. Significant temperature dependence of diffraction pattern was observed.

High-pressure neutron study on silica glass at J-PARC high-pressure neutron diffractometer PLANET

Hattori, Takanori; Yagafarov, O.*; Katayama, Yoshinori; Chiba, Ayano*; Sano, Asami; Inamura, Yasuhiro; Otomo, Toshiya*

no journal, , 

SiO glass is an amorphous solid consisting of SiO tetrahedra. Each tetrahedra are connected to each other, and forms the many-menbered ring. Thus, the glass has large void space and therefore marked densification is expected under pressure. Actually, the density increases by 20% on compression to 8 GPa, accompanying the change in the intermediate range order. The density goes back to the original one on room-temperature decompression, but the high-density state is maintained once the sample is heated under pressure by structural relaxation (permanent densification). So far, the mechanism has been investigated, but remains to be revealed. To reveal the mechanism, in situ high-pressure diffraction is indispensable. Such data were obtained up to 10 GPa at the high-pressure neutron diffactometer PLANET in the last year, therefore we developed the method to analyze the data this year. By developing the program, we succeeded in obtaining structure factor and confirmed its reliability by comparing with the previous results.