Carbon nanothreads (CNThs) are one-dimensional saturated carbon nanomaterials with exceptional mechanical properties. Polycyclic aromatic hydrocarbons (PAHs) are anticipated to form thicker, multi-ring CNThs with improved mechanical performance under high-pressure. Herein, we systematically investigated the high-pressure polymerization of naphthalene, the simplest PAH, using multiple cutting-edge methods. Naphthalene molecules adopt a herringbone stacking along the a-b direction, and underwent reactions along this stacking direction above 20 GPa, affording one-dimensional unsaturated CNThs with the [4+2] cycloaddition reaction as the dominant reaction path. In contrast to the formation of many reported CNThs, the nucleation of the naphthalene-derived CNThs occurs during compression while their growth proceeds during decompression; this behavior is likely common among aromatics with a herringbone structure. The unit cell of the as-obtained CNTh crystal was determined, and a possible structure of the CNTh product was proposed. Our research reveals the polymerization characteristics of naphthalene under high-pressure, highlighting that the slip-angle and herringbone-angle play an important role in governing the polymerization pathway.

Abstract The density of the Earth’s core is lower than that of pure iron; this is considered to be caused by the presence of light elements in the core. Hydrogen is one of the most important light elements in the Earth’s core because of its high cosmochemical abundance and its nature as a siderophile element under high pressure. Thus, the hydrogen content in liquid iron under high pressure is required to constrain the chemical composition of the Earth’s core. However, the hydrogen content has been estimated based on the observation of quench products; there are no examples of hydrogen content being determined in the liquid state. Here, we performed high-pressure and high-temperature neutron diffraction and imaging experiments in situ to determine the hydrogen content in liquid iron. We observed that liquid iron contains 0.17(3) wt% H at 3.4 GPa and 1400 K, indicating that liquid iron is hydrogenated in the magma ocean during core formation. For the hydrogen content in the liquid iron at the base of the magma ocean, we estimated that the outer and inner cores contain 0.60–0.72 and 0.30–0.44 wt% H, corresponding to 70–85 and 1.9–2.7 times the mass of hydrogen in the ocean, respectively. This suggests that hydrogen can contribute more than half of the density deficit in the outer core. For the magma ocean equilibrating with the hydrogen-rich primary atmosphere, the study findings show that liquid iron plays a crucial role in transporting a large amount of hydrogen into the core.

Graphane shares the same two-dimensional honeycomb structure of graphene, but its saturated carbon skeleton gives rise to a bandgap and therefore provides more possibilities for the development of novel carbon-based semiconductors. However, the hydrogenation of graphene usually leads to disordered and incompletely hydrogenated graphane, and the precise synthesis of graphane with a specific configuration is still very challenging. Here, we synthesized a crystalline graphane nanoribbon (GANR) via pressure-induced polymerization of 2,2'-bipyrazine (BPZ). By performing Rietveld refinement of in situ neutron diffraction data, nuclear magnetic resonance spectroscopy, infrared spectra, and theoretical calculation, we found that BPZ experienced Diels-Alder polymerization between the π···π stacked aromatic rings and formed extended boat-GANR structures with exceptional long-range order. The unreacted -C═N- groups bridge the two ends of the boat and are ready for further functionalization. The GANR has a bandgap of 2.25 eV, with booming photoelectric response (ION/IOFF = 18.8). Our work highlights that high-pressure topochemical polymerization is a promising method for the precise synthesis of graphane with specific structure and desired properties.

The Alder-ene reaction is a chemical reaction between an alkene with an allylic hydrogen, and it provides an efficient method to construct the C-C bond. Traditionally, this reaction requires catalysts, high temperatures, or photocatalysis. In this study, we reported a high-pressure-induced solid-state Alder-ene reaction of 1-hexene at room temperature without a catalyst. 1-Hexene crystallizes at 4.3 GPa and polymerizes at 18 GPa, forming olefins. By exploring gas chromatography-mass spectrometry, we discovered that 1-hexene generates dimeric products through the Alder-ene reaction under high pressures. The in situ neutron diffraction shows that the reaction process did not obey the topochemical rule. A six-membered ring transition state including one C-H σ bond and two alkene π bonds was evidenced by the theoretical calculation, whose energy obviously decreased when compressed to 20 GPa. Our work offers a novel and promising method to realize the Alder-ene reaction at room temperature without a catalyst, expanding the application of this important reaction.

The development of effective plastic degradation methods is crucial to address environmental pollution. Hydrothermal liquefaction using near-critical water is a promising technology, but the fundamental dissolution and decomposition mechanisms remain poorly understood. This study investigates the thermodynamics of a polystyrene (PS)/water system under near-critical conditions to elucidate this mechanism. We performed in situ small-angle neutron scattering (SANS) to observe the swelling of PS particles in deuterated water (D2O) at various temperatures under pressures of 10 MPa and 25 MPa. By applying the Flory-Huggins-Staverman (FHS) theory to the swelling data, we quantitatively determined the Flory-Huggins interaction parameter (chi) as a function of temperature and pressure. Based on these results, we constructed a phase diagram of the PS/D2O system. The diagram reveals that miscibility increases with increasing pressure. This work provides the thermodynamic properties of water solutions of polymers under near-critical conditions for optimizing industrial hydrothermal recycling processes.

Mechanochemical radical polymerization has unique advantages in the synthesis of polymers due to its reduced solvent consumption and adaptability of insoluble monomers. However, it suffers from the uncontrollable degradation of the formed polymers during reaction, and a new synthetic strategy with precise controllability needs to be developed. Here, by employing high static pressure up to 30 GPa, we found 1,3,5-trifluorobenzene undergoes radical polymerization by breaking the conjugated π-bonds and forms a carbon nanothread with high selectivity (Polymer-I polymorph). Based on the crystal structure at the threshold pressure and the calculated energy barriers for the bonding pathway, we concluded that the benzene rings react via a radical 1,2-addition pathway. Our work highlights that high pressure is a robust method to initiate solid-state radical polymerization, even for very stable aromatics, and offers fresh insights for the synthesis of polymeric carbon-based materials with high selectivity.

Metal hydroxyhalides with the laurionite-type structure (Pnma, Z = 4) are representatives of studying hydrogen bonds with halogens as proton acceptors. In this study, high-pressure responses of the O-D center dot center dot center dot F hydrogen bonds in deuterated magnesium hydroxyfluoride [ideally Mg(OD)F] were investigated using neutron powder diffraction and Raman spectroscopy. The Rietveld analysis on the neutron powder diffractogram collected under ambient conditions revealed a chemical formula of Mg(OD)0.920(12)F1.080(12) and hydroxyl group/fluorine disorder (OD/F disorder) in the crystal structure, which gave rise to two hydrogen-bonding configurations. The evolution of the hydrogen-bonding geometries under high pressure were obtained from neutron powder diffraction experiments up to 9.8 GPa, evidencing no clear sign of pressure-induced hydrogen bond strengthening. The Raman spectra collected under 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 in Mg(OD)0.920(12)F1.080(12) should be involved in weak or none hydrogen-bonding interactions, though the presence of hydrogen bonds cannot be ruled out. Up to 20.2 GPa, the mode initially centered at 2694 cm-1 displayed a pressure-induced blue shift, revealing that the hydrogen bonds were not strengthened under compression, confirming the conclusion drawn by the neutron diffraction results. Discussions are made on the existence of hydrogen bonds and the causes of the blue-shifting hydroxyls in Mg(OD)0.920(12)F1.080(12) under ambient conditions and at high pressure.

A high-temperature high-pressure cell equipped with a metallic window was developed for small-angle neutron scattering (SANS). The feasibility of a Ti alloy (Ti–6Al–4V) as a candidate window material was assessed, considering its mechanical strength and neutron characteristics. SANS experiments should be conducted using safe and reliable materials without risk of window damage or leakage of the activated samples due to window breakage. SANS profiles measured for supercritical heavy water showed maximum scattering intensity at temperatures and pressures near the critical density. Additionally, the utility of the cell for observations of the decomposition of plastic in supercritical water is presented. The cell facilitates analysis of reaction mechanisms under sub- and supercritical conditions, which could provide detailed information to aid efficient decomposition and recycling, contributing to a sustainable society.

Brucite, Mg(OH)2 (P3m1, Z = 1), is a prototype material for studying hydrogen bonds in solid hydroxides. In this study, substitutional effects of fluorine (F) on the hydrogen-bonding geometries of hydrogenated and deuterated brucite were investigated under ambient conditions and at high pressure using combined experimental methods of neutron powder diffraction, Raman spectroscopy, and infrared (IR) spectroscopy. Under ambient conditions, neutron powder diffraction results showed that F substitution decreased the donor-acceptor distance and increased the hydroxyl covalent bond lengths of both hydrogenated and deuterated brucite, strengthening the hydrogen bond. Red shifts of the hydroxyl stretching modes also indicated an elongation of d(O-H) and d(O-D). High-pressure neutron diffraction experiments were performed on Mg(OH)1.81F0.19 and Mg(OD)1.74F0.26 up to 7.04 and 10.02 GPa, respectively. For both samples, changes in the hydrogen-bonding geometries did not indicate hydrogen-bond strengthening under high pressure. Compared with Mg(OD)2, the doping of F suppressed the increase of the hydroxyl covalent bond length, the hydrogen-bond angle, and the cone angle, inhibiting pressure-induced hydrogen-bond strengthening. High-pressure Raman and IR absorption spectroscopic measurements on Mg(OD)2 and Mg(OD)1.79F0.21 up to 9.7 and 13.7 GPa confirmed that F substitution restrains pressure-induced hydroxyl elongation.

AbstractThe density of the Earth’s core is several percent lower than that of iron-nickel alloy under conditions of pressure and temperature equivalent to the Earth’s core. Hydrogen is one of the most promising constituents accounting for the density deficit, but hydrogen occupation sites and density decrease of iron-nickel alloy caused by hydrogenation have never been investigated. In this study, the phase relation and crystal structure of Fe0.9Ni0.1Hx(Dx) at high pressures and temperatures up to 12 GPa and 1000 K were clarified by in situ X-ray diffraction and neutron diffraction measurements. Under the P-T conditions of the present study, no deuterium atoms occupied tetragonal (T) sites of face-centered cubic (fcc) Fe0.9Ni0.1Dx, although the T-site occupation was previously reported for fcc FeHx(Dx). The deuterium-induced volume expansion per deuterium vD was determined to be 2.45(4) and 3.31(6) Å3 for fcc and hcp Fe0.9Ni0.1Dx, respectively. These vD values are significantly larger than the corresponding values for FeDx. The vD value for fcc Fe0.9Ni0.1Dx slightly increases with increasing temperature. This study suggests that only 10% of nickel in iron drastically changes the behaviors of hydrogen in metal. Assuming that vD 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.

Marine ecosystem degradation due to microplastic pollution is a significant environmental problem, as acknowledged by Sustainable Development Goal 14. Decomposition of plastics using near critical or supercritical water is a promising method to remove microplastics. To optimize this method for realizing environmental benefits, it is necessary to clarify the structural change of materials during the process. Thus, we investigated the decomposition processes of polystyrene particles dispersed in deuterated water (D2O) during heating under near critical or supercritical conditions by using in situ small-angle neutron scattering. Under subcritical conditions, the PS particles were swollen by D2O due to increased compatibility with temperature. In subcritical conditions near the critical point, cleavage of PS chains in the particles occurred, so that the swollen ratio was enhanced despite the PS particles keeping their shapes. Under supercritical conditions, the PS particles were degraded into oil, including oligomers or monomers and phase-separated structures with styrene-rich and D2O-rich regions.

We have performed in situ time‐of‐flight neutron diffraction experiments to examine the uptake of deuterium in iron monosulfide at pressures up to 11.4 GPa and temperatures to 1300 K. A D 2 fluid was formed in the experiments through the decomposition of ND 3 BD 3 , resulting in an oxygen fugacity of approximately 1.2 log units below the iron‐wüstite buffer. Deuterium positions and site occupancies were determined in FeS V, using Rietveld refinements of the powder neutron diffraction patterns. Our structural model indicates that two normally unoccupied sites in the P 6 3 / mmc FeS V structure, at Wyckoff positions 6h and 4f , are partially occupied by D atoms, with the latter being more dominant. The deuterium content D x in FeSD X increases with both pressure and temperature over the experimental conditions explored, from 0.126 (14) at 2.3 GPa and 787 K to 1.20 (16) at 9.7 GPa and 1300 K. The unit‐cell volume expansion per deuterium atom is 1.53 ± 0.16 Å 3 at 6.9 GPa and 960 K, which is smaller than that determined for metallic iron phases at similar conditions. The variation in unit‐cell volume indicates that most deuterium is lost from FeS V upon temperature quenching at high‐pressures. By fitting the obtained FeS V deuterium site occupancies to a thermodynamic model, estimates for the hydrogen contents of iron monosulfide at conditions and oxygen fugacities consistent with the base of the cratonic lithosphere can be made. This results in values in the range of 1,700–2,700 ppm, which contribute to approximately 2–3 ppm hydrogen in the bulk mantle.

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 Ho2Fe17 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 (EF), 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.

This study developed a high-temperature and high-pressure (HTHP) cell for in situ neutron imaging of hydrothermal reactions. The cell's maximum temperature and pressure were 500 °C and 50 MPa, respectively, and its vessel for observing reactions comprised SUS316 stainless steel. Neutron transmission images were obtained to observe the behavior of sub- and supercritical water and the decomposition of two plastics (polypropylene and polyethylene) at HTHP. The images showed that water's density and phase changed with temperature and pressure, affecting neutron transmission (and thus image brightness). The plastics began to melt and change shape at 150-200 °C, and they decomposed at 500 °C and 20 MPa. This study provides a basis for future research using the HTHP cell to examine various reactions such as the decomposition of biomass samples, the reforming of heavy oil, and the synthesis of nano-materials using sub- and supercritical water.

The density of the Earth's core is several percent lower than that of iron-nickel alloy under conditions of pressure and temperature equivalent to the Earth's core. Hydrogen is one of the most promising constituents accounting for the density deficit, but hydrogen occupation sites and density decrease of iron-nickel alloy caused by hydrogenation have never been investigated. In this study, the phase relation and crystal structure of Fe0.9Ni0.1Hx(D-x) at high pressures and temperatures up to 12 GPa and 1000 K were clarified by in situ X-ray diffraction and neutron diffraction measurements. Under the P-T conditions of the present study, no deuterium atoms occupied tetragonal (T) sites of face-centered cubic (fcc) Fe0.9Ni0.1Dx, although the T-site occupation was previously reported for fcc FeHx(D-x). The deuterium-induced volume expansion per deuterium v(D) was determined to be 2.45(4) and 3.31(6) angstrom(3) for fcc and hcp Fe0.9Ni0.1Dx, respectively. These v(D) values are significantly larger than the corresponding values for FeDx. The v(D) value for fcc Fe0.9Ni0.1Dx slightly increases with increasing temperature. This study suggests that only 10% of nickel in iron drastically changes the behaviors of hydrogen in metal. Assuming that v(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.

Underground engineering for processes such as geological disposal of high-level nuclear waste, CO2 capture and storage, and mining and drilling for resources requires an understanding of the mechanical behavior of rocks at subsurface stress states, i.e., triaxial compressive stress. Strain measurement using neutron diffraction can be applied to rocks to analyze strain accumulation mechanisms at the microscopic scale. This study reports the development of triaxial compressive apparatus for strain measurement using neutron diffraction. The apparatus can analyze rock specimens (diameter, 25 mm; length, 50 mm) and apply a maximum confining pressure of 50 MPa. Materials for the components of the apparatus were investigated theoretically based on neutron beam transmission and experimentally using neutron diffraction experiments. The feasibility of the apparatus was verified by measuring strain at hydrostatic pressure under the application of confining pressure and triaxial compression. The theoretical and experimental results show that the apparatus could obtain sufficient neutron statistics from a rock specimen. It was confirmed experimentally that the measured strain values are correlated with the applied confining pressure and stress. The lattice strains of quartz minerals measured by neutron diffraction showed linear deformation behavior, indicating that elastic strain accumulated in the minerals. This apparatus will enable the finding of new insights into the deformation mechanisms of rocks.

We applied Kawai-type multi-anvil assemblies (MA6-8) for time-of-flight neutron-diffraction experiments to achieve high-pressures and high-temperatures simultaneously. To achieve sufficient signal intensities, the angular access to the sample was enlarged using slits and tapers on the first-stage anvils. Using SiC-binder sintered diamond for the second-stage anvils that transmits neutrons, sufficient signal intensities were achieved at a high-pressure of similar to 23.1 GPa. A high-temperature experiment was also conducted at 16.2 GPa and 973 K, validating the use of tungsten carbide for the second-stage anvils. The present study reveals the capability of the MA6-8 cells in neutron-diffraction experiments to attain pressures and temperatures beyond the limits of the conventional MA6-6 cells used in the high-pressure neutron diffractometer PLANET at the MLF, J-PARC.

Neutron di ff raction, Raman spectroscopy, and thermal analysis were performed to investigate the composition, structure, and formation conditions of the magnesium carbonate hydrate nesquehonite. The crystal structure of deuterated nesquehonite was analyzed by Rietveld re fi nement of the time – of – fl ight neutron powder di ff raction pattern. The crystal structure possessed the monoclinic space group P 2 1 / n with lattice parameters of a = 7.72100(12) Å, b = 5.37518(7) Å, c = 12.1430(3) Å, β = 90.165(4)°, and V = 503.956(13) Å 3 . The re fi nement with a fi nal crystal structure model of deuterated nesquehonite converged to wRp = 4.22% and Rp = 3.50%. The result of structure re fi nement showed that two deuterium atoms are coordinated to the O1, O2, and O6 atoms as a water molecule in the nesquehonite. The fact that the three water molecules were included in the structure suggests the structural formula of the nesquehonite obtained in the study should be written as MgCO 3 ·3H 2 O not Mg(HCO 3 )(OH)·2H 2 O.

The rapid increase in the oxidation state of the Earth’s mantle after core formation [1] was a key process in Earth’s development towards habitability. One possibility is that the mantle was oxidised by water, through the reaction H 2 O+2FeO = Fe 2 O 3 +H 2 , delivered during the late stages of accretion [2,3]. However, the resulting H 2 needs to be removed from the mantle to prevent it from reversing the oxidation process. The main phase segregating to the core during the final period of accretion is proposed to be iron sulphide [4]. A viable mechanism to remove H 2 from the mantle would be for it to be incorporated into this FeS melt. Investigating the hydrogen incorporation into FeS is only possible via in-situ methods at high-pressures ( P ) and high-temperatures ( T ), since H 2 exsolves from FeS during quenching. We performed in-situ high-pressure time-of-flight neutron diffraction experiments on the FeS–H(D) system using a six-axis multi-anvil press installed at the PLANET beamline (BL-11), J-PARC , Japan. Thermal decomposition of deuterated ammonia borane (ND 3 BD 3 ) supplied deuterium to the FeS starting material