ABSTRACT Conformational changes in ionic liquids (ILs) under high pressure (HP) are closely related to pressure-induced phase transitions. The HP-induced conformational preferences (trans–gauche equilibrium for the N–C–C–C dihedral angle) of two 1-propyl-3-methylimidazolium-based ILs ([C3mim][X]; X= I and BF4) were investigated up to approximately 8 GPa using Raman spectroscopy. The trans conformer of [C3mim][I] increased monotonically with increasing pressure up to 8 GPa. Conversely, the trans conformer of [C3mim][BF4] decreased with increasing pressure up to 2.4 GPa and then increased up to 5.8 GPa. Subsequently, the conformational distribution remained constant up to approximately 8 GPa. The difference in the HP-induced conformational changes between these two [C3mim]+-based ILs were attributed to the anion position relative to the cation, unlike the [C4mim]+-based ILs. These findings provide insight into the role of cation–anion interactions in determining IL behavior under extreme conditions, which is crucial for their applications in HP environments.

ABSTRACT Triaxial deformation experiments on olivine aggregates were conducted at pressures of 1.3–3.4 GPa and temperatures of 670–1160 K under nominally dry and water-saturated conditions. The maximum strength of olivine was found to be well described by a reported flow law for dry olivine controlled by Peierls creep. Vigorous acoustic activity followed by faulting was recorded in the olivine samples deformed to a maximum stress of ∼2 GPa at 1070–1160 K. In contrast, acoustic emissions were less active and faulting was absent at lower temperatures (670–950 K) even though the maximum stress exceeded 2.5 GPa in these runs. Our observations suggest that processes that promote microcracking (e.g. kinking and microfaulting), rather than elevated stress magnitude, are necessary for the occurrence of faulting.

ABSTRACT High-pressure electron spin resonance techniques offer a powerful approach for investigating the effects of pressure on magnetic materials from a microscopic perspective. Among these techniques, the thermal detection method can be combined with a split-pair-type superconducting magnet owing to its compactness, allowing for field-angle-dependent measurements. By applying this technique to the spin-gap compound Cu 2 (C 5 H 12 N 2 ) 2 Cl 4 , which exhibits a marked pressure dependence, we found that the local square-pyramidal crystal field of the Cu 2 + magnetic ion is deformed under pressure. This deformation suggests a significant modification of the ferromagnetic interactions within the Cu binuclear unit.

ABSTRACT The pressure-induced phase transition behavior of the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([C4dmim][BF4]) in the crystalline state was investigated by Raman spectroscopy at 298 K. The observed spectral changes indicate that four phase transitions may occur up to 8 GPa. The obtained results were compared with those reported in a previous study on supercooled [C4dmim][BF4], where crystallization occurred at ∼1.3 GPa and unexpectedly, only the gauche conformer was present in the high-pressure crystalline state. Typically, the trans conformer dominates the crystalline structures of most imidazolium-based ILs at high-pressures. This study reports two unique pressure-induced phase transition patterns in [C4dmim][BF4], highlighting the different conformational behavior under applied pressure.

ABSTRACT Filled skutterudite compounds have attracted attention due to their excellent thermoelectric properties and various anomalous properties specific to strongly correlated electron systems such as metal-nonmetal transition, multipole ordering, and heavy electron state. Filled skutterudite compounds containing heavy rare-earth elements are extremely difficult to synthesize at ambient pressure. However, we have succeeded in synthesizing new filled skutterudite compounds containing heavy rare-earth elements by high pressure synthesis methods. We report high pressure synthesis and magnetic properties of ROs4P12 (R = Gd, Tb, Dy, and Ho), which are difficult to obtain at ambient pressure. We discuss the crystal field ground states, magnetic phase diagrams and the role of multipole degree of freedom, in these compounds.

ABSTRACT We have conducted the AC magnetization measurement for high-quality HgBa2Ca2Cu3O8 + δ specimens synthesized by high-pressure synthesis, using a miniature diamond anvil cell (DAC) and various pressure-transmitting media such as Daphne-7373 oil, Apiezon-J oil, fluorine-oil mixture, methanol–ethanol mixture, and liquid oxygen. There were two trends in the pressure dependence of superconducting transition temperature (T c), and they reveal how hydrostatic compression is necessary to increase T c effectively. The optimal T c in the present experiments is 153 K, which is consistent with T c determined by zero resistance using a cubic anvil cell. Hydrostatic compression using a cubic anvil is more effective in increasing T c than a somewhat uniaxial style using DAC.

ABSTRACT Yb-based intermediate-valence quasicrystals (IV-QCs) are known to exhibit robust quantum criticality against both applied physical and chemical pressure. In this study, we investigated the pressure dependance of the Yb mean valence (ν) in the quantum-critical Au–Al–Yb QC. We newly identified a critical pressure of 5.8 GPa at which a valence anomaly emerges. Furthermore, high pressure XRD measurements were performed to compare the effects of physical and chemical pressure, revealing that both lead to similar ν- a 6 D curves with a nearly identical critical Yb mean valence, although the anomaly is much sharper and the critical lattice parameter differs in the case of chemical pressure. These new findings provide valuable clues toward elucidating the origin of quantum criticality in IV-QCs.

ABSTRACT Investigating materials under extreme pressure using diamond anvil cells (DACs) requires very small samples. X-ray diffraction studies of such samples therefore require beams focused to < 5 μ m . Fortuitously, advances in light-source and beamline design mean that modern synchrotrons, such as PETRA III and ESRF-EBS, now deliver sub-μm focusing. Combined with increased source brightness, fast motors, user-friendly control interfaces, and data processing advances, 2D mapping of microscopic samples becomes routine, with exposures on mid-Z samples reduced to seconds. We demonstrate the use of sub-μm beams, with high-resolution 2D scans, to map pressure and strain gradients. We show how small scans are applied to collect optimum data, and how the sample can affect the pressure inferred from the pressure calibrant. Although sub-μm beams can improve compressibility data, they may also introduce undersampling, revealing variability on μm length scales. We provide recommendations for the use of sub-μm beams for extreme conditions research.

ABSTRACT We investigated phase relations in the CaSiO3–MgSiO₃ system through multi-anvil phase-equilibrium experiments and time-resolved in-situ X-ray diffraction measurements on diopside and related compositions. Under equilibrium conditions at 23–25 GPa and 2100 K, all starting materials decomposed into MgSiO₃ bridgmanite and CaSiO3 davemaoite. However, a (Ca,Mg)SiO3 CM-perovskite appeared transiently during the rapid decomposition of diopside in the in-situ XRD measurements. Its kinetic stability increased markedly at lower temperatures and higher pressures, and the phase was observed up to 2100 K at ∼40 GPa, indicating strong kinetic stabilization under high-pressure conditions. These results suggest that preservation of CM-perovskite found in a shocked meteorite requires extremely rapid quenching during the shock event. It also stresses that phase-equilibrium experiments – particularly at higher pressures than 40 GPa – must be interpreted carefully, as metastable perovskite compositions can readily appear during transformation processes.

ABSTRACT A relationship between density of solid FeS and that of coexisting liquid Fe–S is crucial for understanding the Martian core structure. In the sulfur-rich Martian core (S > 25 wt%), FeS could be a liquidus phase. In this study, the density of FeS V phase was measured using the X-ray absorption method combined with a laser-heated DAC up to 26 GPa and 1950K. The density from the X-ray absorption method is consistent with that from X-ray diffraction (0.04–2.82% in difference). The density of FeS is found to be lower than that of the liquid Fe–30wt%S at the Martian core pressures. Therefore, solid FeS could float in the liquid Fe–S core. The solid FeS outer core may influence the weak Martian magnetic field. If Mars has a solid inner core, FeS is excluded from the liquidus phases in the core, indicating that the sulfur content in the core is constrained to be <25 wt%.