In laser-heated diamond anvil cell (DAC) experiments, the effective heated region typically decreases in size with increasing pressure, leading to steeper thermal gradients. Under these conditions, chromatic aberration in the optical path from sample to detector can significantly create bias in spectro-radiometric temperature measurement. We present a radiance-mapping approach using a hyperspectral camera that records 25 spectral channels spanning 605-875 nm at each pixel in a single exposure, providing spatially and spectrally resolved radiance in each frame. This enables chromatic effects to be recorded and corrected in data processing. We developed a procedure for hyperspectral mapping, involving per-camera calibration, crosstalk removal, measured spectral throughput functions, and optional sub-pixel co-registration to minimize chromatic distortion. The calibrated radiance maps are then used to derive temperature maps of the laser-heated hotspots. For smaller heating spots, the radiance mapping approach reveals chromatic shifts that conventional spectro-radiometric methods cannot quantify. Ambient-pressure heating experiments confirm accurate temperature retrieval. At high pressure, application of the hyperspectral system to a platinum-heating experiment at 12 GPa demonstrates stable temperature reconstruction under steep thermal gradients. Beyond mitigating chromatic aberrations, the ability to diagnose optical artifacts separately from emissivity variations during controlled test experiments or in situ suggests a path toward more rigorous spectral emissivity analysis and improved modeling of thermal transport in laser-heated DAC experiments.

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.

Beamline 16-BM-B of the High-Pressure Collaborative Access Team (HPCAT) at the Advanced Photon Source (APS) provides a Paris-Edinburgh press program to probe the structure and properties of crystalline and amorphous materials up to 12 GPa at room temperature or 7 GPa at 2000$<^>\circ$degrees C. During the recent APS upgrade, 16-BM-B undertook major improvements to its instrumentation and measurement techniques. The upgrade includes the addition of a 1.2 m horizontal "condenser" mirror and a new variable-sized collimation system, the combination of which decreases the acquisition time for energy dispersive X-ray diffraction measurements by a factor of 10 when compared to pre-upgrade measurements. The addition of a new Ge energy-sensitive detector and DANTE (XGLab) digital pulse processor allows for processing the increased diffraction counts with minimal deadtime. In addition to upgraded beamline components, new techniques are being developed for eventual release to the user community, including electrical resistivity and tomography measurements.

Accurate pressure calibration is fundamental to quantitative high-pressure science, yet inconsistencies among widely used secondary pressure scales persist. We report simultaneous synchrotron x-ray diffraction meatogether in diamond anvil cells to 140 GPa. This simultaneous-measurement strategy minimizes transitive errors and run-to-run inconsistencies inherent to paired-measurement approaches, yielding direct experimental volume-volume (V-V) relations among the calibrants. These V-V relations link the compression state of each phase to that of every other phase measured in the same experiment. By anchoring these V-V relations to the reduced 300 K equation of state (EOS) of copper derived from ramp-compression measurements, we derive an internally consistent set of Cu-referenced pressure scales via Vinet EOS fits. Because the primary experimental result is the V-V dataset, it provides an EOS-independent constraint that can be rereferenced if primary standards are revised. The dataset further enables a direct experimental cross-check of consistency between the adopted reduced 300 K Cu EOS and the corresponding reduced 300 K ramp-derived EOSs for Pt, Au, Ta, and hcp-Fe under a fixed V-V constraint. The residuals quantify small, material-dependent mismatches between each phase EOS and the Cu reference EOS.

In this study, we investigated pressure-induced changes in the structure and elastic properties of xAl2O3-(100 - x)SiO2 glasses (x = 29, 36, 43, 50, 60 mol%; referred to as xAS) by in situ high-pressure pair distribution function measurement and sound velocity measurement. The 29AS and 60AS glasses are regarded as Si-rich/Al-rich end-member compositions, and the 36AS, 43AS, and 50AS glasses consist of the two end-member phases at the nanoscale. The 29AS glass shows gradual changes in the intermediate-range order up to 9.3 GPa, similar to SiO2 glass, while the 60AS glass exhibits a rapid structural change at 7.4-8.4 GPa, similar to CaAl2O4 glass. This rapid structural change causes a kink in the sound velocity-pressure trend near 8 GPa, as also observed in CaAl2O4 glass. In contrast, the Si-rich end-member 29AS glass does not exhibit the velocity kink. The Poisson's ratios of the five AS glasses and the SiO2 glass start to converge above similar to 11 GPa, finally reaching a constant value of similar to 0.32 at a pressure of similar to 20 GPa. This result indicates that both the Si-rich and Al-rich end-members have a similar structure above similar to 20 GPa.

The pressure-temperature phase behavior of covalent disordered solids such as amorphous silicon and germanium is complex. Questions remain on possible glass transitions, on polyamorphism via amorphous-amorphous transitions, on connections with liquid-liquid transitions, on structure-behavior relationships, and on their potential as precursor for novel methods for material discovery. Here we demonstrate experimentally the nucleation of a metastable, four-fold coordinated rhombohedral r8 phase from pure amorphous silicon and germanium upon room temperature compression at pressures below 10 GPa. Accompanying theory reveals a strong pressure-driven distortion of the bond angle transforming the starting tetrahedral low-density amorphous network to a distorted four-fold coordinated medium-density state. This state is of lower density than metallic high-density networks, resembles the crystalline r8 phase and initiates its nucleation. Our finding shows that polyamorphism is not the only possible transformation mode for these amorphous solids and that instead nucleation of interesting functional phases at potentially useful pressures is possible. Such novel access modes to metastable structures are critical for future exploitability and could be useful for other tetrahedral materials including carbon, where the related (bc8) post-diamond phase remains elusive. Our observed density match between an amorphous and a metastable crystalline phase clearly allows for a new phase transition pathway, while corresponding theory demonstrates how carefully validated atomistic simulations can guide prediction, discovery and synthesis of novel material structures.

Electronic responses of glasses under extreme pressures differ from those of crystalline analogs. Their distinct electronic environments are found in network formers with well-defined, covalent-bonded coordination environments (e.g., [4]Si and [4]Al) and in network modifiers with more disordered, ionic-bonded configurations (e.g., [5,6,7]Ca). Deciphering the evolution of the bonding environment of network modifier cations upon compression provides atomic insights into the pressure-driven hardening and transport properties of glasses. Despite the importance, in contrast to extensive efforts to uncover how network formers behave under pressure, considerable structural disorder around network modifiers makes it challenging to probe their electronic bonding environments under compression. Our understanding of the evolution of network modifiers above megabars is currently absent. Here, we report a discovery of highly densified electronic configurations of network modifier Ca in aluminate glass under extreme compression via the first inelastic X-ray scattering at the Ca L-edge up to 140 GPa. As evidenced by the prominent pressure-driven increases in electronic dispersion and delocalization, densified calcium environments are characterized by a decreased average Ca-O distance, the formation of highly coordinated calcium, a broader distribution of topological variables, and a greater distortion of Ca polyhedra above megabars. The spectral features for the Ca environments reveal significant electronic and bonding modifications, including pressure-driven increases in the ligand field interaction, the covalence characteristic of the Ca-O bond, and the electron-hole Coulomb interaction. These densification paths identify the electronic adaptation of network modifiers above megabars, shedding light on the origins of enhanced electron transport and the electron-storing capacity of glasses under pressure.

The formation of carbon-carbon interlinkage bonds (CCIBs) via the chemical binding of interlayer carbon atoms of many sp2-bonded carbon precursors is an essential step for synthesizing various diamond and diamond-like materials. Although the existence of CCIBs may be reasonably assumed under high-pressure conditions, direct experimental evidence has been scarce. Micro-Raman spectroscopy is here employed to track in situ the evolution of C-C bonds in a pressure range from ambient to 54 GPa. A pressure-induced two-stage (polynomial and linear) shift of the G peak and new generation of the CCIB peak at about 1550 cm-1 are observed in multiple types of layer-structured carbon precursors, including glassy carbon, natural graphite, and carbon nanotubes. The experimental discovery of CCIBs holds significance in comprehending phase transitions of sp2-bonded carbon materials and has implications for the advancement of novel carbon structures.

Cu2IrO3 has attracted recent interest due to its proximity to the Kitaev quantum spin liquid state and the complex structural response observed at high pressures. We use x-ray spectroscopy and scattering as well as electrical transport techniques to unveil the electronic structure of Cu2IrO3 at ambient and high pressures. Despite featuring a Ir4+ Jeff = 1/2 state at ambient pressure, Ir L3-edge resonant inelastic x-ray scattering reveals broadened electronic excitations that point to the importance of Ir 5d-Cu 3d interaction. High pressure first drives an Ir-Ir dimer state with collapsed (L S) and (Lz)/(Sz), signaling the formation of 5d molecular orbitals. A novel Cu -* Ir charge transfer is observed above 30 GPa at low temperatures, leading to an approximate Ir3+ and Cu1.5+ valence, with persistent insulating electrical transport seemingly driven by charge segregation of Cu1+/Cu2+ ions into distinct sites. Concomitant x-ray spectroscopy and diffraction measurements through different thermodynamic paths demonstrate a strong electron-lattice coupling, with Jeff = 1/2 and Ir3+/Cu1.5+ electronic states occurring only in phases 1 and 5, respectively. Remarkably, the charge-transfer state can only be reached if Cu2IrO3 is pressurized at low temperature, suggesting that phonons play an important role in the inhibiting this phase. These results point to the choice of thermodynamic path across interplanar collapse transition as a key parameter to access novel states in intercalated iridates.

We have measured the luminescence shift of the ruby's R1-line corresponding to the transition pressure of bismuth (Bi) I-II. The Bi sample was loaded in a diamond anvil cell using neon as pressure medium, with small ruby spheres positioned near the Bi sample. Fine compression and decompression were controlled by a double-sided membrane system. Synchrotron x-ray diffraction measurements on Bi and luminescence measurements on ruby were simultaneously collected using an in-line ruby system at the 16-ID-B beamline at the Advanced Photon Source. The Bi I-II transformation is signified by the distinct diffraction patterns, associated with discontinuities in the luminescence shift as a function of time. The determined ruby's R1-shift is 0.9311 +/- 0.007 nm at the Bi I-II transition at 25.8 +/- 0.1 degrees C. Together with the previously determined R1-shift relative to the melting pressure of mercury, the calibrations constrain the initial slope of ruby gauge to 1860 +/- 3 GPa, compared to 1870 +/- 10 GPa in the Ruby2020 gauge.

We evaluate pressure consistency of equations of state (EOS) for NaCl and Au at 300 K. The simultaneous measurements of unit-cell volumes (V) with ruby R1 line shifts (Delta lambda) in a helium (He) loaded diamond cell effectively remove potential systematic errors. Compression and decompression data were automatically collected at 1 sec interval, yielding a dense dataset with >8,000 (V, Delta lambda) pairs each for NaCl and Au. Solidification of He has noticeable effects on both V and Delta lambda (hence P). Only data up to similar to 14 GPa, or 6000 (V, P) pairs, can be considered hydrostatic within the resolution. The P-V data are fitted to the Rydberg-Vinet and the 3(rd) order Birch-Murnaghan EOS. Predicted pressures of these EOSs agree with those given by the Ruby2020 ruby scale to within +/- 0.05 GPa. Overall, pressures predicted by the Rydberg-Vinet EOS are in better agreement with the average of commonly used NaCl and Au pressure scales.

Inelastic x-ray scattering (IXS) of B2O3 glass up to ∼2.2 Mbar reveals electronic bonding transitions in oxide glasses. B -edge IXS identifies the high-energy feature above ∼1.4 Mbar and a gradual increase in its intensity toward ∼2.2 Mbar, indicating the formation of hypervalent boron via electron polarization to oxygen atoms. The pressure-driven high energy shifts in O -edge IXS indicate pronounced electronic dispersion that increases upon densification of amorphous oxides above ∼2 Mbar. The extent of the energy shifts and enhanced polarization correlate with increasing atomic radius of cation in oxide glass, establishing the role of cation radius in electronic structures of amorphous oxides under compression. The results elucidate the electronic mechanisms behind the structural transformation in low- oxide glasses, where transitions to highly coordinated cations are hindered well above 1 Mbar, providing the origin of incompressibility of low- amorphous oxide under multi-Mbar compression. Published by the American Physical Society 2024

Pressure-dependent synchrotron x-ray diffraction (XRD), nuclear resonant inelastic x-ray scattering (NRIXS), and nuclear forward scattering (NFS) measurements were made on 57 Fe 55 Ni45. 45 . XRD measurements were at 298 and 392 K at pressures up to 20 GPa, confirming a pressure-induced Invar effect between 7 and 13 GPa. A decrease of the 57 Fe magnetic moment was found in NFS measurements under pressure, showing an increase in magnetic entropy. The 57 Fe phonon density of states (DOS) was obtained from NRIXS measurements. The low thermal expansion in the high-pressure Invar region originates from a competition between the thermal expansion from spins and phonons as calculated from Maxwell relations. The longitudinal phonon modes changed their pressure dependence near the Curie transition, which is evidence for a spin-phonon interaction.

The speciation of iodine in basalts has been investigated by combining in situ X-ray diffraction at high pressures and temperatures up to 4.9 GPa and 1600 °C, and Raman spectroscopy on recovered high pressure glasses at ambient conditions. Both methods point to iodine being oxidized in basalts, whether molten or quenched as glasses. Observed interatomic distances and Raman vibrational modes are consistent with iodine being dissolved as complex iodate groups alike polyiodates or periodates, not as $\mathrm{IO}_3^-$ groups. Iodine speciation in basalts therefore seems to reflect a trend amongst halogens, with lighter chlorine bonding to network modifying cations, and bromine changing affinity from network modifying cations to oxygen anions under pressure. In the absence of a fluid aqueous phase, iodine could thus reach the Earth’s surface in basaltic magmas as an oxide, not as a reduced species.

The diamond anvil cell (DAC) has been widely used in high-pressure research. Despite significant progress over the past five decades, the opposed anvil geometry in the DAC inevitably leads to a disk-shaped sample configuration at high pressure. This intrinsic limitation is largely responsible for the large pressure and temperature gradients in the DAC, which often compromise precise experiments and their characterizations. We designed and fabricated a multi-axis diamond anvil cell (MDAC) by adopting the concept of a multi-anvil apparatus but using single crystal diamonds as the anvil material. Preliminary data show that the MDAC can generate extreme pressure conditions above 100 GPa. The advantages of the MDAC over a traditional opposed anvil DAC include thicker, voluminous samples, quasi-hydrostatic, or designed deviatoric stress conditions, and multidirectional access windows for optical applications and x-ray probes. In this article, we present the design and performance of a prototype MDAC, as well as the application prospects in high-pressure research.

Many aromatic polymers undergo shock-induced transformations above 15 GPa, often with significant volume collapses. While the mechanisms responsible for these transformations remain unclear due to challenges in combining in situ characterization with dynamic compression, static compression is a viable alternative. In-situ energy dispersive X-ray diffraction experiments (EDXD) were carried out at room temperature and up to 32 GPa in polyurea, an amorphous aromatic elastomer used in armor applications. Measurements were performed with a double -stage compression technique developed at sector 16 of the Advanced Photon Source in a large volume Paris -Edinburgh press. Signatures of a transformation were observed in the total structure factors and pair distribution functions (PDF) between 11-16 GPa, including a shift to larger bond lengths and an apparent increase in 1st and 2nd coordination numbers. The transformation appears to be driven by a disruption in the intermediate range order arising from interchain distances and the subsequent formation of cross -linkages between neighboring chains. This study illustrates the advantages of studying amorphous polymers using the double-stage static compression technique and EDXD.

The detailed study of the effect of the initial microstructure on its evolution under hydrostatic compression before, during, and after the irreversible alpha -> omega phase transformation and during pressure release in Zr using in situ x-ray diffraction is presented. Two samples were studied: one is plastically pre-deformed Zr with saturated hardness and the other is annealed. Phase transformation alpha -> omega initiates at lower pressure for a pre-deformed sample but for a volume fraction of omega Zr, c > 0.7, a larger volume fraction is observed for the annealed sample. This implies that the proportionality between the athermal resistance to the transformation and the yield strength in the continuum phase transformation theory is invalid; an advanced version of the theory is outlined. Phenomenological plasticity theory under hydrostatic loading is outlined in terms of microstructural parameters, and plastic strain is estimated. During transformation, the first rule is suggested, i.e., the average domain size, microstrain, and dislocation density in omega Zr for c < 0.8 are functions of the volume fraction, c of omega Zr only, which are independent of the plastic strain tensor prior to transformation and pressure. The microstructure is not inherited during phase transformation. Surprisingly, for the annealed sample, the final dislocation density and the average microstrain after pressure release in the omega phase are larger than for the severely pre-deformed sample. The results suggest that an extended experimental basis is required for the predictive models for the combined pressure-induced phase transformations and microstructure evolutions. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Metallophilicity has been widely studied as a fundamental supramolecular interaction. However, the extent and directionality thereof remain controversial. A major obstacle lies in the difficulty to separately control the geometry and chemical composition. Herein, we address this challenge by modulating metallophilicity with mechanical pressure. Using a multinuclear Cu(I) complex as model system, we report anomalous anisotropies of (supra)molecular structures, vibrations, and interaction energies upon isotropic compression as well as concomitant (essentially turn-on) piezochromic luminescence enhancement with ∼103 modulation. The in situ characterizations indicate opposite behaviors of contact distances and cuprophilic interactions for intermolecular vs intramolecular Cu-Cu pairs under pressure. Theoretical calculations break down the attractive and repulsive forces associated with cuprophilicity, its spontaneous 4p-3d hybridization origin, and direction-dependent interaction strength. The use of isotropic mechanical force reveals the intrinsic anisotropy of metallophilicity in multinuclear systems.

Diamond shows unprecedented hardness. Because hardness is a measure of resistance of chemical bonds in a material to external indentation, the electronic bonding nature of diamond beyond several million atmospheres is key to understanding the origin of hardness. However, probing the electronic structures of diamond at such extreme pressure has not been experimentally possible. The measurements on the inelastic x-ray scattering spectra for diamond up to 2 million atmospheres provide data on the evolution of its electronic structures under compression. The mapping of the observed electronic density of states allows us to obtain a two-dimensional image of the bonding transitions of diamond undergoing deformation. The spectral change near edge onset is minor beyond a million atmospheres, while its electronic structure displays marked pressure-induced electron delocalization. Such electronic responses indicate that diamond’s external rigidity is supported by its ability to reconcile internal stress, providing insights into the origins of hardness in materials.