The Earth's core is believed to contain some light elements because it is 10% less dense than pure Fe under the corresponding pressure and temperature conditions. Hydrogen, a promising candidate among light elements, has phase relations and physical properties that have been investigated mainly for the Fe-H system. This study specifically examined an Fe-Si-H system using in-situ neutron diffraction experiments to investigate the site occupancy of deuterium of hcp-Fe0.95Si0.05 hydride at 14.7 GPa and 800 K. To date, this pressure condition is the highest for neutron diffraction experiments conducted at high pressure and high temperature, where crystal structure analysis has been conducted. Results of Rietveld refinement indicate hcp-Fe0.95Si0.05 hydride as having deuterium (D) occupancy of 0.24(2) exclusively at the interstitial octahedral site in the hcp lattice. The effect on the site occupancy of D by addition of 2.6 wt% Si into Fe (Fe0.95Si0.05) was negligible compared to results obtained from an earlier study of an Fe-D system (Machida et al., 2019).

Crystal structures of alkali metal hydrogen carbonates are affected by pressure. Previous studies showed that KHCO₃ has a phase transition at around 2.8 GPa, room temperature. This study discovered that RbHCO₃ transformed into a high-pressure phase at around 0.5 GPa, room temperature. As for CsHCO₃, no phase transition was observed up to 5 GPa. These results suggested that the pressure-induced behaviors of alkali metal hydrogen carbonates were systematically related to their cation radii.

Ultrafine-grained (0.2-0.3μm) WC-Ni hardmetals with a low Ni content (3-5wt%) were developed using new production techniques based on adding an appropriate amount of VC and Cr3C2, combined with the strong mixing of raw materials. Their uniaxial compressibility was subsequently compared with that of existing WC-Ni and WC-Co hardmetals to assess their suitability for use as anvils in various high pressure experiments, particularly those associated with neutron or magnetic studies. The ultimate compressive strength of the newly developed hardmetals was over 7.7GPa, which was higher by 1.2GPa than that of the existing WC-Ni hardmetal MF10. When these hardmetals were used as anvils, a pressure of approximately 16GPa was generated using a Paris-Edinburgh-type apparatus with φ8mm culet, thereby proving that they can allow the physical properties of various materials to be measured at higher pressures than is possible with existing hardmetals.

X-ray radiography was applied to observe the segregation process of iron from silicate at high pressure and high temperature in mixtures containing light elements. As the temperature of the hydrogen-containing sample increases, the molten iron becomes coherent. Small droplets of iron sink to the bottom of the chamber, where they merge into a single, large droplet. The small iron droplets exhibit complex motion, moving in random directions. Markedly different behavior is found in the sulfur-containing sample, where no clear motion of the molten iron is observed. Instead, as the sample temperature is increased, the concentration of iron near the wall of the sample chamber gradually increases. These observations demonstrate that the behavior of molten iron changes according to the dissolved elements. This X-ray radiography experiment represents a powerful technique to study the segregation process of molten iron from solid or partially molten silicate, particularly when combined with high-resolution tomography techniques.

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 11.9GPa. This is comparable to anvils made of tungsten carbide (TC) with Ni binder with the same dimensions. ATZ would also be an alternative material to TC with pressure performance comparable to ZTA, whereas YSZ is much weaker than the other two ceramics. The attenuation coefficient for YSZ is significantly smaller than that of TC and similar to ZTA and ATZ, the latter being estimated by attenuation calculations. Neutron diffraction on a sample of lead in YSZ anvils as well as quasi-elastic neutron scattering on liquid water in ZTA also demonstrate the outstanding neutron transparency of these ceramics. The gain factor in count rate is up to one order of magnitude.

A new opposed-anvil high pressure and temperature apparatus was developed based on the Drickamer-type apparatus. Various improvements were made to increase the sample volume and to generate high pressure and temperature stably and easily. By optimizing components such as the anvil, heater, and gasket, large sample volumes of about 4mm 3 (∼10 3 times more than that previously obtained with our previous apparatus) were achieved, with compact and light apparatus (outer diameter φ 40mm; height 31mm; weight 300g). Pressures and temperatures up to about 15GPa and 1700K can routinely and stably be achieved by using this assembly. In order to extend the pressure range further, sintered diamond was used as an anvil material. As a result, pressures and temperatures of around 38GPa and 1400K were achieved, although the sample volume was decreased to about 1.3∼10 -1mm 3. © 2011 Taylor and Francis.

We designed a new cell assembly of diamond anvil cells for single crystal x-ray diffraction under pressure and demonstrate the application of the cell to the crystallographic studies for ice VI and ethanol high-pressure (HP) phase at 0.95(5) GPa and 1.95(2) GPa, respectively. The features of the assembly are: (1) the platy anvil and unique-shaped backing seat (called as Wing seat) allowing the extremely wide opening angle up to ±65°, (2) the PFA-bulk metallic glass composite gasket allowing the easy attenuation correction and less background. Thanks to the designed assembly, the Rint values after attenuation corrections are fairly good (0.0125 and 0.0460 for ice VI and ethanol HP phase, respectively), and the errors of the refined parameters are satisfactory small even for hydrogen positions, those are comparable to the results which obtained at ambient conditions. The result for ice VI is in excellent agreement with the previous study, and that for ethanol HP phase has remarkable contributions to the revision to its structure; the H12 site, which makes gauche molecules with O1, C2, and C3 sites, may not exist so that only trans conformers are present at least at 1.95(2) GPa. The accurate intensities using the cell assembly allow us to extract the electron density for ethanol HP phase by the maximum entropy method. © 2011 American Institute of Physics.

Infrared absorption spectra of δ-AlOOH and its deuterated form (δ-AlOOD) were measured at high pressure using a diamond anvil cell under a quasi-hydrostatic pressure condition using helium as a pressure-transmitting medium. Two absorption bands at 1180 cm-1and 1330 cm-1 involving vibrations of hydrogen and oxygen atoms shifted to higher frequencies with increasing pressure up to 10 and 12 GPa for δ-AlOOH and δ-AlOOD, respectively. In contrast, at higher pressures the two bands did not shift so much. The pressure-response on the infrared spectra has a close relationship to the symmetrization of the hydrogen bonds and change in the compressibility which was observed from X-ray diffraction measurements. © 2010 IOP Publishing Ltd.

The compression behaviors of δ-AlOOH and δ-AlOOD were investigated under quasi-hydrostatic conditions at pressures up to 63.5 and 34.9 GPa, respectively, using results from synchrotron X-ray diffraction experiments conducted at ambient temperature. Because of the geometric isotope effect, at ambient pressure, the a and b axes of δ-AlOOD, which define the plane in which the hydrogen bond lies, are longer than those of δ-AOOH. Under increasing pressure, the a and b axes of δ-AlOOH stiffen at 10 GPa, although the c axis shows no marked change. Identical behavior was found in δ-AlOOD, but the change in compressibility was observed at a slightly higher pressure of 12 GPa. Axial ratios a/c and b/c first decrease rapidly with increasing pressure, then begin to increase at pressures >10 GPa in δ-AlOOH and >12 GPa in δ-AlOOD. At these pressures, the pressure dependence of a/b also changes from increasing to decreasing. The unit-cell volumes of δ-AlOOH and δ-AlOOD become slightly less compressible at high pressures. Assuming K0' = 4, the calculated bulk moduli of δ-AlOOH below and above 10 GPa are 152(2) and 219(3) GPa, respectively. Those of δ-AlOOD below and above 12 GPa are 151(1) and 207(2) GPa, respectively.

A method was proposed for measuring infrared absorption spectra at high pressure under quasi-hydrostatic pressure conditions. Two KBr micro-pellets were prepared as samples, and reference materials were charged in a diamond anvil cell, applying helium as the pressure-transmitting medium. Using this method, the quasi-hydrostatic pressure condition was retained up to approximately 20GPa. Furthermore, hydrostaticity was much better than conventional pressure-transmitting media used for infrared spectroscopy. Infrared absorption spectra of α -FeOOH at high pressure were measured using the KBr micro-pellet method with a helium pressure-transmitting medium. Downshift of the OH stretching vibration was observed with increasing pressure. Use of the KBr micro-pellet method for infrared absorption spectroscopy at high pressure is a complementary experimental technique to neutron diffraction at high pressure for studying the pressure response of hydrogen bonds.

含水鉱物の圧縮挙動は物質の構造変化に直接的に関連し、地球内部での大規模現象における有用な情報を与えうることから、近年、水素結合を含む物質の圧力応答に関する研究が進められてきた。常圧でも強い水素結合をもつ炭酸水素カリウムKHCO₃は、結晶構造中で２つのHCO₃^－イオンが水素結合によって二量体を形成している。この二量体の配向秩序が変化することで、圧力や温度誘起による相転移が起こる。しかし、この物質の相転移圧力への同位体効果はいまだ明らかではない。本研究では、DACを用いた、単結晶KHCO₃とKDCO₃の圧力相転移前後のラマンスペクトルと結晶の外形の変化の精密なその場観察から、圧力誘起相転移における同位体効果の存在の確認と相転移メカニズムの検証を行った。