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Journal Articles

Brightening triplet excitons enable high-performance white-light emission in organic small molecules via integrating n-$$pi^*/pi$$-$$pi^*$$ transitions

Yang, Q.*; Yang, X.*; Wang, Y.*; Fei, Y.*; Li, F.*; Zheng, H.*; Li, K.*; Han, Y.*; Hattori, Takanori; Zhu, P.*; et al.

Nature Communications (Internet), 15, p.7778_1 - 7778_9, 2024/09

https://doi.org/10.1038/s41467-024-52196-7

Luminescent materials that simultaneously embody bright singlet and triplet excitons hold great potential in optoelectronics, signage, and information encryption. However, achieving high-performance white-light emission is severely hampered by their inherent unbalanced contribution of fluorescence and phosphorescence. Herein, we address this challenge by pressure treatment engineering via hydrogen bonding cooperativity effect to realize the mixture of n-$$pi^*/pi$$-$$pi^*$$ transitions, where the triplet state emission was boosted from 7% to 40% in isophthalic acid (IPA). A superior white-light emission based on hybrid fluorescence and phosphorescence was harvested in pressure-treated IPA, and the photoluminescence quantum yield was increased to 75% from the initial 19% (blue-light emission). In-situ high-pressure IR spectra, X ray diffraction, and neutron diffraction reveal continuous strengthening of the hydrogen bonds with the increase of pressure. Furthermore, this enhanced hydrogen bond is retained down to the ambient conditions after pressure treatment, awarding the targeted IPA efficient intersystem crossing for balanced singlet/triplet excitons population and resulting in efficient white-light emission. This work not only proposes a route for brightening triplet states in organic small molecule, but also regulates the ratio of singlet and triplet excitons to construct high-performance white-light emission.

Journal Articles

Hydroxyl group/fluorine disorder in deuterated magnesium hydroxyfluoride and behaviors of hydrogen bonds under high pressure

He, X.*; Kagi, Hiroyuki*; Komatsu, Kazuki*; Iizuka, Riko*; Okajima, Hajime*; Hattori, Takanori; Sano, Asami; Machida, Shinichi*; Abe, Jun*; Goto, Hirotada*; et al.

Journal of Molecular Structure, 1310, p.138271_1 - 138271_8, 2024/08

https://doi.org/10.1016/j.molstruc.2024.138271

High-pressure responses of the O-D$$cdotcdotcdot$$F hydrogen bonds in deuterated magnesium hydroxyfluoride were investigated using neutron powder diffraction and Raman spectroscopy. The Rietveld analysis at ambient conditions revealed a chemical formula of Mg(OD)$$_{0.920(12)}$$F$$_{1.080(12)}$$ and hydroxyl group/fluorine disorder (OD/F disorder) in the crystal structure, which gave rise to two hydrogen-bonding configurations. The Rietveld analysis showed the hydrogen-bonding geometries remains up to 9.8 GPa, indicating no pressure-induced strengthening of hydrogen bonds. The Raman spectra at ambient conditions showed three hydroxyl stretching bands at 2613, 2694, and 2718 cm$$^{-1}$$. The high frequencies of the O-D stretching modes indicated that the hydroxyls should be involved in weak or none hydrogen-bonding interactions. Up to 20.2 GPa, the mode initially centered at 2694 cm$$^{-1}$$ displayed a pressure-induced blue shift, revealing no strengthening of hydrogen bonds under compression. We discuss the existence of hydrogen bonds and the causes of the blue-shifting hydroxyls at ambient and at high pressures.

Journal Articles

Giant barocaloric effects in sodium hexafluorophosphate and hexafluoroarsenate

Zhang, Z.*; Hattori, Takanori; Song, R.*; Yu, D.*; Mole, R.*; Chen, J.*; He, L.*; Zhang, Z.*; Li, B.*

Journal of Applied Physics, 136(3), p.035105_1 - 035105_8, 2024/07

https://doi.org/10.1063/5.0211085

Solid-state refrigeration using barocaloric materials is environmentally friendly and highly efficient, making it a subject of global interest over the past decade. Here, we report giant barocaloric effects in sodium hexafluorophosphate (NaPF$$_6$$) and sodium hexafluoroarsenate (NaAsF$$_6$$) that both undergo a cubic-to-rhombohedral phase transition near room temperature. We have determined that the low-temperature phase structure of NaPF$$_6$$ is a rhombohedral structure with space group R$=3 by neutron powder diffraction. There are three Raman active vibration modes in NaPF$_6$$ and NaAsF$$_6$$, i.e., F$$_{2g}$$, E$$_g$$, and A$$_{1g}$$. The phase transition temperature varies with pressure at a rate of dT$$_t$$/dP = 250 and 310 K/GPa for NaPF$$_6$$ and NaAsF$$_6$$. The pressure-induced entropy changes of NaPF$$_6$$ and NaAsF$$_6$$ are determined to be around 45.2 and 35.6J kg$$^{-1}$$K$$^{-1}$$, respectively. The saturation driving pressure is about 40 MPa. The pressure-dependent neutron powder diffraction suggests that the barocaloric effects are related to the pressure-induced cubic-to-rhombohedral phase transitions.

Journal Articles

Hydrogen bond symmetrisation in D$$_2$$O ice observed by neutron diffraction

Komatsu, Kazuki*; Hattori, Takanori; Klotz, S.*; Machida, Shinichi*; Yamashita, Keishiro*; Ito, Hayate*; Kobayashi, Hiroki*; Irifune, Tetsuo*; Shimmei, Toru*; Sano, Asami; et al.

Nature Communications (Internet), 15, p.5100_1 - 5100_7, 2024/06

https://doi.org/10.1038/s41467-024-48932-8

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 transition pressures reported up to date remain inconsistent. Here we report the atomic distribution of deuterium in D$$_2$$O ice using neutron diffraction above 100 GPa and observe for the first time the transition from a bimodal to a unimodal distribution of deuterium at around 80 GPa. At the transition pressure, a significant narrowing of the peak widths of 110 was also observed, attributed to the structural relaxation by the change of elastic properties.

Journal Articles

Development of 0.5 mm gauge size radial collimators for high-pressure neutron diffraction experiments at PLANET in J-PARC

Hattori, Takanori; Suzuki, Koji*; Miyo, Tatsuya*; Ito, Takayoshi*; Machida, Shinichi*

Nuclear Instruments and Methods in Physics Research A, 1059, p.168956_1 - 168956_9, 2024/02

https://doi.org/10.1016/j.nima.2023.168956
 Times Cited Count：0 Percentile：0.02(Instruments & Instrumentation)

Radial collimators (RC) with a 0.5 mm gauge size (GS) were specially designed for high-pressure neutron diffraction experiments and their performance and efficacy were investigated. The RCs with nominal GS of 0.75 mm, 1.5 mm, and 3.0 mm effectively exhibited GS of 0.50 mm, 1.07 mm, and 2.78 mm, respectively. The transmissions of all three RCs were almost equivalent. The assessment using a P-E press and a DAC revealed that the anvil scattering was considerably minimized and the sample-to-anvil signal ratio reached values of 0.5 and 2.0 for the PE press and DAC, respectively, when using the 0.5 mm-GS RCs. These results indicate that the 0.5mm-GS RCs have been fabricated as intended and exhibit efficacy for the high-pressure-neutron diffraction experiments, specifically those exceeding 30 GPa. Among those ever manufactured for neutron scattering experiments, the RCs display the smallest GS.

Journal Articles

Anisotropic electrical conductivity changes in FeTiO$$_3$$ structure transition under high pressure

Yamanaka, Takamitsu*; Nakamoto, Yuki*; Sakata, Masafumi*; Shimizu, Katsuya*; Hattori, Takanori

Physics and Chemistry of Minerals, 51(1), p.4_1 - 4_10, 2024/02

https://doi.org/10.1007/s00269-023-01261-6
 Times Cited Count：0 Percentile：0.10(Materials Science, Multidisciplinary)

Neutron and synchrotron X-ray diffraction and electric conductivity measurements of FeTiO$$_3$$ ilmenite were performed under pressures. Ilmenite structure is retained up to 28 GPa. Structure analysis revealed that FeO$$_6$$ and TiO$$_6$$ are compressible and less compressible below 8 GPa, respectively. The resistivity is lowest along the Fe-Ti direction that has shortest interatomic distance among all the metal ion pairs. The resistivity in the direction normal to c-axis monotonically decreases with pressure, whereas that along c-axis shows hallow-shape with pressure. Maximum entropy analysis shows that electron configuration of Fe$$^{2+}$$ (3$$d^6$$) is more strongly changed than Ti$$^{4+}$$ (3$$d^0$$) under compression. The anisotropic electrical conductivity and non-uniform structure change of Fe-Ti interatomic distance can be explained by the possible spin transition from high-spin state to intermediate-spin state of Fe cation.

Journal Articles

Slightly hydrogen-ordered state of ice IV evidenced by ${it in situ}$ neutron diffraction

Kobayashi, Hiroki*; Komatsu, Kazuki*; Ito, Hayate*; Machida, Shinichi*; Hattori, Takanori; Kagi, Hiroyuki*

Journal of Physical Chemistry Letters (Internet), 14(47), p.10664 - 10669, 2023/11

https://doi.org/10.1021/acs.jpclett.3c02563
 Times Cited Count：1 Percentile：44.88(Chemistry, Physical)

Ice IV is a metastable high-pressure phase of ice in which the water molecules exhibit orientational disorder. Although orientational ordering is commonly observed for other ice phases, it has not been reported for ice IV. We conducted ${it in situ}$ powder neutron diffraction experiments for DCl-doped D$$_{2}$$O ice IV to investigate hydrogen ordering in ice IV. We found abrupt changes in the temperature derivative of unit cell volume, dV/dT, at about 120 K, and revealed their slightly ordered structure at low temperatures based on the Rietveld method. The occupancy of the D1 site deviates from 0.5; it increased when samples were cooled at higher pressures and reached 0.282(5) at 2.38 GPa, 58 K. Our results evidence the presence of a low-symmetry hydrogen-ordered state corresponding to ice IV. It seems, however, difficult to experimentally access the completely ordered phase corresponding to ice IV by slow cooling at high pressure.

Journal Articles

The Hydrogen-bond network in sodium chloride tridecahydrate; Analogy with ice VI

Yamashita, Keishiro*; Nakayama, Kazuya*; Komatsu, Kazuki*; Ohara, Takashi; Munakata, Koji*; Hattori, Takanori; Sano, Asami; Kagi, Hiroyuki*

Acta Crystallographica Section B; Structural Science, Crystal Engineering and Materials (Internet), 79(5), p.414 - 426, 2023/10

https://doi.org/10.1107/S2052520623007199
 Times Cited Count：0 Percentile：0.02(Chemistry, Multidisciplinary)

The structure of a recently-found hyperhydrated form of sodium chloride, NaCl$$cdot$$ 13H(D)$$_{2}$$O, has been determined by ${it in situ}$ single-crystal neutron diffraction at 1.7 GPa and 298 K. It has large hydrogen-bond networks and some water molecules have distorted bonding features such as bifurcated hydrogen bonds and five-coordinated water molecules. The hydrogen-bond network has similarities to ice VI in terms of network topology and disordered hydrogen bonds. Assuming the equivalence of network components connected by pseudo symmetries, the overall network structure of this hydrate can be expressed by breaking it down into smaller structural units which correspond to the ice VI network structure. This hydrogen-bond network contains orientational disorder of water molecules in contrast to the known salt hydrates. Here, we present an example for further insights into a hydrogen-bond network containing ionic species.

Journal Articles

An X-ray and neutron scattering study of aqueous MgCl$$_2$$ solution in the gigapascal pressure range

Yamaguchi, Toshio*; Fukuyama, Nami*; Yoshida, Koji*; Katayama, Yoshinori*; Machida, Shinichi*; Hattori, Takanori

Liquids (Internet), 3(3), p.288 - 302, 2023/09

https://doi.org/10.3390/liquids3030019

We report the structure of an aqueous 2 mol/kg MgCl$$_2$$ solution at pressures from 0.1 MPa to 4 GPa and temperatures from 300 to 500 K revealed by X-ray and neutron scattering measurements. The scattering data are analyzed by empirical potential structure refinement (EPSR) modeling to derive the pair distribution functions, coordination number distributions, angle distributions, and spatial density functions as a function of pressure and temperature. Mg$$^{2+}$$ forms rigid solvation shells extended to the third shell; the first solvation shell of six-fold octahedral coordination with about six water molecules at 0 GPa transforms into about five water molecules and one Cl$$^-$$ due to the formation of the contact ion pairs in the GPa pressure range. The Cl$$^-$$ solvation shows a substantial pressure dependence; the coordination number of a water oxygen atom around Cl$$^-$$ increases from 8 at 0.1 MPa/300 K to 10 at 4 GPa/500 K. The solvent water transforms the tetrahedral network structure at 0.1 MPa/300 K to a densely packed structure in the GPa pressure range; the number of water oxygen atoms around a central water molecule gradually increases from 4.6 at 0.1 MPa/298 K to 8.4 at 4 GPa/500 K.

Journal Articles

Pressure engineering of van der Waals compound RhI$$_3$$; Bandgap narrowing, metallization, and remarkable enhancement of photoelectric activity

Fang, Y.*; Kong, L.*; Wang, R.*; Zhang, Z.*; Li, Z.*; Wu, Y.*; Bu, K.*; Liu, X.*; Yan, S.*; Hattori, Takanori; et al.

Materials Today Physics (Internet), 34, p.101083_1 - 101083_7, 2023/05

https://doi.org/10.1016/j.mtphys.2023.101083
 Times Cited Count：1 Percentile：44.21(Materials Science, Multidisciplinary)

The layered van der Waals halides are particularly sensitive to external pressure, suggesting a feasible route to pinpoint their structure with extraordinary behavior. However, a very sensitive pressure response usually lead to a detrimental phase transition and/or lattice distortion, making the approach of materials manipulation in a continuous manner remain challenging. Here, the extremely weak interlayer coupling and high tunability of layered RhI$$_3$$ crystals are observed. A pressure-driven phase transition occurs at a moderate pressure of 5 GPa, interlinking to a change of layer stack mode. Strikingly, such a phase transition does not affect the tendency of quasi-linear bandgap narrowing, and a metallization with an ultra-broad tunability of 1.3 eV redshift is observed at higher pressures. Moreover, the carrier concentration increases by 4 orders of magnitude at 30 GPa, and the photocurrent enhances by 5 orders of magnitude at 7.8 GPa. These findings create new opportunities for exploring, tuning, and understanding the van der Waals halides by harnessing their unusual feature of a layered structure, which is promising for future devices based on materials-by-design that are atomically thin.

Journal Articles

Hydrogen occupation and hydrogen-induced volume expansion in Fe$$_{0.9}$$Ni$$_{0.1}$$D$$_x$$ at high $$P-T$$ conditions

Shito, Chikara*; Kagi, Hiroyuki*; Kakizawa, Sho*; Aoki, Katsutoshi*; Komatsu, Kazuki*; Iizuka, Riko*; Abe, Jun*; Saito, Hiroyuki*; Sano, Asami; Hattori, Takanori

American Mineralogist, 108(4), p.659 - 666, 2023/04

https://doi.org/10.2138/am-2022-8348
 Times Cited Count：1 Percentile：54.63(Geochemistry & Geophysics)

The phase relation and crystal structure of Fe$$_{0.9}$$Ni$$_{0.1}$$H$$_x$$ (D$$_x$$) at high pressures and temperatures up to 12 GPa and 1000 K were clarified by in-situ X-ray and neutron diffraction measurements. Under $$P-T$$ conditions of the present study, no deuterium atoms occupied tetragonal ($$T$$) sites of face-centered cubic (fcc) Fe$$_{0.9}$$Ni$$_{0.1}$$D$$_x$$ unlike fcc FeH$$_x$$(D$$_x$$). The deuterium-induced volume expansion per deuterium $$v_mathrm{D}$$ was determined as 2.45(4) $AA$^3$$ and 3.31(6) $AA$^3$$ for fcc and hcp phases, respectively, which were significantly larger than the corresponding values for FeD$$_x$$. The $$v_mathrm{D}$$ value slightly increased with increasing temperature. This study suggests that only 10% of nickel in iron drastically changes the behaviors of hydrogen in metal. Assuming that $$v_mathrm{D}$$ is constant regardless of pressure, the maximum hydrogen content in the Earth's inner core is estimated to be one to two times the amount of hydrogen in the oceans.

Journal Articles

Pressure-modulated magnetism and negative thermal expansion in the Ho$$_2$$Fe$$_{17}$$ intermetallic compound

Cao, Y.*; Zhou, H.*; Khmelevskyi, S.*; Lin, K.*; Avdeev, M.*; Wang, C.-W.*; Wang, B.*; Hu, F.*; Kato, Kenichi*; Hattori, Takanori; et al.

Chemistry of Materials, 35(8), p.3249 - 3255, 2023/04

https://doi.org/10.1021/acs.chemmater.3c00158
 Times Cited Count：1 Percentile：40.78(Chemistry, Physical)

Hydrostatic and chemical pressure are efficient stimuli to alter the crystal structure and are commonly used for tuning electronic and magnetic properties in materials science. However, chemical pressure is difficult to quantify and a clear correspondence between these two types of pressure is still lacking. Here, we study intermetallic candidates for a permanent magnet with a negative thermal expansion (NTE). Based on in situ synchrotron X-ray diffraction, negative chemical pressure is revealed in Ho$$_2$$Fe$$_{17}$$ on Al doping and quantitatively evaluated by using temperature and pressure dependence of unit cell volume. A combination of magnetization and neutron diffraction measurements also allowed one to compare the effect of chemical pressure on magnetic ordering with that of hydrostatic pressure. Intriguingly, pressure can be used to control suppression and enhancement of NTE. Electronic structure calculations indicate that pressure affected the top of the majority band with respect to the Fermi level, which has implications for the magnetic stability, which in turn plays a critical role in modulating magnetism and NTE. This work presents a good example of understanding the effect of pressure and utilizing it to control properties of functional materials.

Journal Articles

A Colossal barocaloric effect induced by the creation of a high-pressure phase

Jiang, X.*; Hattori, Takanori; Xu, X.*; Li, M.*; Yu, C.*; Yu, D.*; Mole, R.*; Yano, Shinichiro*; Chen, J.*; He, L.*; et al.

Materials Horizons, 10(3), p.977 - 982, 2023/03

https://doi.org/10.1039/d2mh00905f
 Times Cited Count：6 Percentile：89.86(Chemistry, Multidisciplinary)

As a promising environment-friendly alternative to current vapor-compression refrigeration, solid-state refrigeration based on the barocaloric effect has been attracting world wide attention. Generally, both phases in which a barocaloric effect occurs are present at ambient pressure. Here, instead, we demonstrate that KPF$$_{6}$$ exhibits a colossal barocaloric effect due to the creation of a high-pressure rhombohedral phase. The phase diagram is constructed based on pressure-dependent calorimetric, Raman scattering, and neutron diffraction measurements. The present study is expected to provide an alternative routine to colossal barocaloric effects through the creation of a high-pressure phase.

Journal Articles

Neutron scattering on an aqueous sodium chloride solution in the gigapascal pressure range

Yamaguchi, Toshio*; Yoshida, Koji*; Machida, Shinichi*; Hattori, Takanori

Journal of Molecular Liquids, 365, p.120181_1 - 120181_10, 2022/11

https://doi.org/10.1016/j.molliq.2022.120181
 Times Cited Count：1 Percentile：13.89(Chemistry, Physical)

Neutron scattering measurements were performed on an aqueous 3 mol/kg NaCl solution in D$$_2$$O at temperature and pressure conditions of 0.1 MPa/298K, 1 GPa/298K, 1 GPa/523K, and 4 GPa/523K. The empirical potential structure refinement method was applied to the obtained data to extract the pair correlation function, coordination number distribution, angular distribution (orientation correlation), and spatial density function (3-D structure). From those results, pressure and temperature dependence of solvation and association of ions and solvent-water structure were discussed.

Journal Articles

Hydrogen vibration excitations of ZrH$$_{1.8}$$ and TiH$$_{1.84}$$ up to 21 GPa by incoherent inelastic neutron scattering

Hattori, Takanori; Nakamura, Mitsutaka; Iida, Kazuki*; Machida, Akihiko*; Sano, Asami; Machida, Shinichi*; Arima, Hiroshi*; Oshita, Hidetoshi*; Honda, Takashi*; Ikeda, Kazutaka*; et al.

Physical Review B, 106(13), p.134309_1 - 134309_9, 2022/10

https://doi.org/10.1103/PhysRevB.106.134309
 Times Cited Count：0 Percentile：0.00(Materials Science, Multidisciplinary)

Hydrogen vibration excitations of fluorite-type ZrH$$_{1.8}$$ and TiH$$_{1.84}$$ were investigated up to 21 GPa and 4 GPa, respectively, by incoherent inelastic neutron scattering experiments. The first excitation energies increased with pressure, as described by the equations $$E_1$$(meV) = 141.4(2) + 1.02(2)$$P$$(GPa) and $$E_1$$(meV) = 149.4(1) + 1.21(8)$$P$$(GPa) for ZrH$$_{1.8}$$ and TiH$$_{1.84}$$, respectively. Coupling with pressure dependence of lattice parameters, the relations between metal-hydrogen distance ($$d_{M-H}$$) and $$E_1$$ are found to be well described by the equations $$E_1$$(meV) = 1.62(9)$$times$$ 10$$^3$$ $$d_{M-H}^{-3.31(8)}$$($AA) and $E_1$$(meV) = 1.47(21)$$times$$ 10$$^3$$ $$d_{M-H}^{-3.5(2)}$$(AA), respectively. The slopes of these curves are much steep compared to the previously reported trend in various fluorite-type metal hydrides at ambient pressure. The hydrogen wave function spreading showed that the local potential field for a hydrogen atom shrinks more intensively than the tetrahedral site. These behavior is likely caused by the rigid metal ion core and the resulting confinement of the hydrogen atom in the narrower potential field at high pressures.

Journal Articles

Magnetic and structure transition of Mn$$_{3-x}$$Fe$$_x$$O$$_4$$ solid solutions under high-pressure and high-temperature conditions

Yamanaka, Takamitsu*; Hirao, Naohisa*; Nakamoto, Yuki*; Mikouchi, Takashi*; Hattori, Takanori; Komatsu, Kazuki*; Mao, H.-K.*

Physics and Chemistry of Minerals, 49(10), p.41_1 - 41_14, 2022/10

https://doi.org/10.1007/s00269-022-01215-4
 Times Cited Count：0 Percentile：0.02(Materials Science, Multidisciplinary)

Magnetic and crystal structure of Mn$$_{3-x}$$Fe$$_x$$O$$_4$$ solid solutions under high-PT conditions are investigated by neutron diffraction and synchrotron M${"o}$ssbauer spectroscopy. The ferrimagnetic-paramagnetic transition and tetragonal-cubic transition of Mn$$_2$$FeO$$_4$$ spinel occur at 100$$^circ$$C and 180$$^circ$$C, respectively, suggesting both the transitions are not coupled. The structure transition temperature decreases with pressure. M${"o}$ssbauer experiments and neutron diffraction revealed that the Fe$$^{2+}$$ occupancy in tetrahedral site increases increase with pressure, suggesting Mn$$_2$$FeO$$_4$$ phase approaches inverse spinel. Magnetic structure refinement clarified paramagnetic and ferrimagnetic structure of MnFe$$_2$$O$$_4$$ and Mn$$_2$$FeO$$_4$$. These spinels transform into high-pressure orthorhombic phases at 18.4 and 14.0 GPa, respectively, indicating lower transition pressure with increasing Mn content.

Journal Articles

Atomic distribution and local structure in ice VII from in situ neutron diffraction

Yamashita, Keishiro*; Komatsu, Kazuki*; Klotz, S.*; Fabelo, O.*; Fern$'a$ndez-D$'i$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

https://doi.org/10.1073/pnas.2208717119
 Times Cited Count：2 Percentile：19.02(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.

Journal Articles

Enhancement of electrical conductivity to metallization of Mn$$_{3-x}$$Fe$$_x$$O$$_4$$ spinel and postspinel with elevating pressure

Yamanaka, Takamitsu*; Rahman, S.*; Nakamoto, Yuki*; Hattori, Takanori; Jang, B. G.*; Kim, D. Y.*; Mao, H.-K.*

Journal of Physics and Chemistry of Solids, 167, p.110721_1 - 110721_10, 2022/08

https://doi.org/10.1016/j.jpcs.2022.110721
 Times Cited Count：1 Percentile：13.39(Chemistry, Multidisciplinary)

High-pressure neutron diffraction proved that MnFe$$_2$$O$$_4$$ and Mn$$_2$$FeO$$_4$$ spinels transform into CaMn$$_2$$O$$_4$$-type structure above 18 GPa and 14 GPa, respectively. The transition pressure of Mn$$_{3-x}$$Fe$$_x$$O$$_4$$ solutions decreases with increasing Mn content. Synchrotron X-ray M$"{o}$ssbauer experiments revealed that Fe$$^{2+}$$ and Fe$$^{3+}$$ distribution at the tetrahedral (A) and octahedral (B) sites in the spinel structure changes with pressure. MnFe$$_2$$O$$_4$$ and Mn$$_2$$FeO$$_4$$ spinels are ferrimagnetic and the CaMn$$_2$$O$$_4$$-type phase is paramagnetic. The temperature dependence of resistivity indicates that both spinels are semiconductors wherein electrons hop between cations at the A and B sites. A pressure-induced shortening of B-B distance promoted conduction via greater electron mobility between adjacent B cations. The Fe$$^{2+}$$ and Fe$$^{3+}$$ occupancies at the B sites in MnFe$$_2$$O$$_4$$ are much larger than those in Mn$$_2$$FeO$$_4$$. The CaMn$$_2$$O$$_4$$-type phase is metallic. Theoretical calculation confirmed the metallic character and Fe d-orbitals strongly renormalized compared to Mn d-orbitals.

Journal Articles

High-pressure neutron experiments at PLANET in J-PARC using the six-axis multi-anvil press ATSUHIME

Hattori, Takanori

Yukuatsu Gijutsu, 61(7), p.29 - 35, 2022/07

As an example of the application of hydraulic technology, the 6-axis type multi-anvil press "ATSUHIME" in the J-PARC ultra-high pressure neutron diffractometer PLANET and the research on hydrogen in the Earth's core using them are introduced.

Journal Articles

Structure of basaltic glass at pressures up to 18 GPa

Ohashi, Tomonori*; Sakamaki, Tatsuya*; Funakoshi, Kenichi*; Hattori, Takanori; Hisano, Naoki*; Abe, Jun*; Suzuki, Akio*

American Mineralogist, 107(3), p.325 - 335, 2022/03

https://doi.org/10.2138/am-2021-7742
 Times Cited Count：1 Percentile：19.16(Geochemistry & Geophysics)

The basaltic glass structure were investigated to 18 GPa using in situ X-ray and neutron diffraction. The O-O coordination number (CN$$_textrm{OO}$$) starts to rise with maintaining the mean O-O distance (r$$_textrm{OO}$$) above 2-4 GPa, and then CN$$_textrm{OO}$$ stops increasing and r$$_textrm{OO}$$ begins to shrink along with the increase in the Al-O coordination number (CN$$_textrm{AlO}$$) above 9 GPa. This is interpreted by the change in the contraction mechanism from tetrahedral network bending to oxygen packing ratio increase via the CN$$_textrm{AlO}$$ increase. The oxygen packing fraction exceeds the value for dense random packing, suggesting that the oxygen-packing hypothesis cannot account for the pressure-induced structural transformations of silica and silicate glasses. The CN$$_textrm{OO}$$ increase at 2-4 GPa reflects the elastic softening of silicate glass, which may causes anomalous elastic moduli of basaltic glass at $$sim$$ 2 GPa.

302 (Records 1-20 displayed on this page)