ABSTRACT A high pressure H-type electrochemical cell was developed to enable collection and quantitative analysis of gaseous and liquid electrolysis products. Owing to the use of transparent chambers, the volume of evolved gas can be estimated. The cell includes septum-sealed sampling ports on cathodic and anodic chambers, allowing direct gas and liquid sampling using syringes after depressurizing to ambient pressure. This setup enables quantitative evaluation of overall product distribution under pressure, providing a comprehensive view of pressure-dependent reaction selectivity. As a demonstration, CO2 electrolysis was performed under hydrostatic pressures of up to 50 MPa, during which key CO2 reduction products (CO, CH4, and C2H4) and H2 from the hydrogen evolution reaction were detected. These results demonstrate that the cell can operate reliably at pressures up to 50 MPa while providing quantitative access to evolved products, indicating its suitability for mechanistic studies of electrochemical reactions involving both gaseous and dissolved products.

ABSTRACT In this study, we developed an optical pump-probe spectroscopy measurement system that operates at high pressures and low temperatures by combining a diamond anvil cell with a commercially available cryostat. The current setup allows for optical measurements at pressures up to 10 GPa and temperatures as low as approximately 13 K. As a demonstration, we examined the effects of pressure on the photo-induced pseudogap formation at a temperature T g of approximately 70 K in the organic superconductor κ-(BEDT-TTF) 2 Cu(NCS) 2 . At a pressure of 0.8 GPa, we observed changes in transient reflectivity associated with pseudogap formation occurring below approximately 200 K, which is above T g . This finding suggests that pressure influences the electron-phonon interaction, leading to the development of a pseudogap at higher temperatures.

ABSTRACT We investigated pressure-induced phases in the organic dimer–Mott insulators β ′ - ( BEDT - TTF ) 2 CF 3 CF 2 SO 3 and β ′ - ( BEDT - TTF ) 2 SF 5 CF 2 SO 3 [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene] by measuring their electrical resistivity under pressures up to 12 GPa utilizing a cubic-anvil cell. Although previous high-pressure studies on BEDT-TTF salts using cubic anvil techniques achieved a maximum pressure of approximately 10 GPa, the use of an MgO gasket and Daphne 7373 as the pressure-transmitting medium in this study enabled stable measurements up to 12 GPa. Increasing pressure produced a substantial reduction in room-temperature resistivity, and both salts exhibited insulator–metal transitions. Near the Mott boundary, a pronounced decrease in resistivity was observed at low temperatures. Although zero resistance was not achieved, this behavior is consistent with that of a superconductivity precursor. These findings indicate that the vicinity of the Mott critical pressure is a promising regime for superconductivity in β ′ -type dimer–Mott systems and demonstrate the effectiveness of cubic-anvil high-pressure transport measurements for systematic exploration of this regime.

ABSTRACT In 1997, AIRAPT recommended a set of room-temperature pressure reference points (PRPs) for the large-volume press (LVP) community, known as the Practical International Pressure Scale (PIPS-97). With recent AIRAPT-recommended ruby scale Ruby2020 for diamond-anvil cell (DAC) experiments, it is now necessary to re-examine PIPS-97 for consistency with the DAC pressure scale. We reconstruct equations of state (EOSs) for NaCl and Au that are explicitly tied to Ruby2020 and recalculate the PRPs using these EOSs. The revised PRP values are given. GaAs is removed from the PRP list because of the complexity of its phase transitions. The ZnS value, although retained, requires further investigation. Overall, the revised pressures are systematically higher than PIPS-97 by up to 4% at 35 GPa. We propose that this updated set of PRPs, referred to as PIPS-2025, be adopted for LVP experiments to improve pressure consistency between the LVP and DAC communities.

ABSTRACT The superconducting transition temperature T c of compressed barium (Ba) has been reported to increase with pressure (P) up to ≈8 K under low-temperature compression [Jackson et al., Phys. Rev. B 96, 184,514 (2017)]. However, those measurements were interpreted only through a previously established phase diagram without simultaneous structural determination. We calculated T c for several candidate structures using first-principles methods, and compared them with the experimental trends. The experimental pressures are offset by ≈10 GPa in comparison to our results, likely due to non-equilibrium effects caused by compression at ≈10 K. After accounting for this offset, we argue that the data assigned to the Ba-VI phase cannot be explained by a single structure. The T c(P) slope below ≈20 GPa corresponds to the stable hexagonal close-packed Ba-II phase, whereas above ≈20 GPa it follows Pnma-related metastable structures. These results demonstrate that the T c(P) slope provides a reliable structural fingerprint for identifying the superconducting phases in compressed Ba.

ABSTRACT This study investigates the structural, mechanical and thermodynamic properties of MAX phase compounds Zr2GeN and Zr2GeF under pressure ranging from 0 to 18 GPa using DFT. The simulations were performed with the VASP code integrated into the MedeA software. The equilibrium lattice parameters and elastic constants confirm that both compounds have structural and mechanical stability. The negative formation and cohesive energies suggest that the two compounds are synthesizable and energetically stable. Zr2GeN is stiffer and less compressible than Zr2GeF because its Young's and bulk moduli are higher. Thermodynamic analysis shows that heat capacities (CV and CP) increase with temperature, while the Grüneisen parameter decreases with pressure, indicating enhanced lattice stability. The findings offer valuable insights into how Zr-based MAX phases behave under pressure and may support the development of materials for high-pressure, high-temperature applications.

ABSTRACT A novel diamond anvil cell design is presented with significant improvements in precision, operation, and manufacturing. It is building up from the known ‘plate’ cells, further minimizing even small shear forces, that are most likely responsible for the frequent and unnecessary damage or failure of costly diamond anvils. This diamond cell accommodates high resolution microscope objectives with short working distance to obtain sharp Raman spectra of the diamond/sample interface for precise pressure measurements.

ABSTRACT Magnesite is recognized as a key host of oxidized carbon in the subducted slabs and plays a fundamental role in transporting and storing carbon into the deep Earth. Here, we investigate the stability of magnesite at 14 GPa, 900–1700°C, and oxygen fugacity ( f O 2 ) from the nickel-nickel oxide (Ni-NiO) to iron-wüstite (IW) buffers, using a multi-anvil apparatus. Using ex-situ Raman spectroscopy and ex-situ scanning electron microscopy energy-dispersive spectroscopy, we demonstrate that the magnesite-diamond/graphite boundary along hot slab geotherms tends to occur at higher oxygen fugacity compared to the average mantle, reaching values above IW+3.5 at 14 GPa. We further model that, along cold slab geotherms, magnesite can retain its stability even under highly reduced conditions, whereas it would transform into graphite along hot slab geotherms.

ABSTRACT We used density functional theory calculations to explore the structural, elastic, and thermodynamic properties of the Zintl phases CaZn2P2 and CaZn2As2 under hydrostatic pressure. The excellent agreement between predicted structural features and experimental data validates our method. The [001] crystal orientation demonstrates greater compressibility in both compounds compared to the [100] direction. The anticipated monocrystalline elastic constants for both compounds meet mechanical stability criteria up to 18 GPa. We also examined the polycrystalline mechanical properties. Pugh's ratio, Poisson's ratio, and Cauchy pressure suggest the materials are brittle. The quasiharmonic Debye approximation was utilized to assess the dependence of key macroscopic physical parameters, including lattice constants, bulk modulus, volumetric thermal expansion coefficient, Debye temperature, and both isobaric and isochoric heat capacities, on temperature at constant pressures of 0, 4, 8, 12, and 16 GPa. The agreement between elastic constant data and the Debye quasiharmonic results confirms the reliability of our findings.

ABSTRACT We present a simple method for determining equations of state (densities) of liquids up to 10 GPa based on a precise measurement of the volume of the gasket hole in a diamond anvil cell. Key ingredients are the use of a highly sensitive optical pressure gauge, in our case SrClF:Sm2+ and ruby, the preparation of gaskets which maintain a well-defined geometry of the sample chamber, and the application of corrections due to the elasticity of the diamonds. We show that, following a certain procedure, the method allows under favorable conditions measurements of the equations of state with a precision of 1–3%. Results on the equation of state of the 4:1 methanol–ethanol mixture as well as of Daphne fluids 7474 and 7676 are presented. Measurements on water to 5.5 GPa allow a direct evaluation of the precision of the method.