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The authors perform heating experiments using femtosecond X-ray free electron laser pulses to explore the phase stability of superionic H₂O. The absence of a face-centered cubic phase below 50 GPa, where superionic ice forms from the melt, is attributed to the short heating time and may help understanding the stability of superionic phases in ice-rich planets.

Fe₂O₃is known to undergo a series of structural, electronic and magnetic transformations at high pressures and temperatures but these are poorly understood due to a lack of structural data. Here, the authors perform experiments to elucidate the transformations and relationships between them.

Experimental evidence shows that hydrogen–silicate reactions can generate abundant water in sub-Neptunes, suggesting hydrogen-rich planets have the potential to reach water-rich compositions.

Excited state dynamics of alloyed quantum dots differ from that of binary quantum dots. Here, the authors use femtosecond spectroscopy and theoretical calculations to show that alloying tunes relaxation dynamics separately from traditional optical properties of quantum dots.

Earth’s core exhibits similar elastic properties to rubber. Experiments show that a high-pressure phase of iron carbide modifies iron’s elastic properties under inner-core conditions, suggesting that carbon is the light element in the core.

As silica melts are believed to be important components of the Earth’s mantle, their structure should determine many of its properties. Here, the authors identify two crystalline modifications of SiO₂, whose local structures closely resemble those of known melts, providing a structural model for their atomic ordering at the nanoscale.

Pressures of up to 900 gigapascals (9 million atmospheres) are achieved in a laser-heated double-stage diamond cell, enabling the synthesis of Re₇N₃, and materials characterization is performed in situ using single-crystal X-ray diffraction.

Superconductivity in hydrides has been primarily explored by electrical transport measurements. Here, the authors perform SQUID magnetometry under extreme high-pressure and report characteristic superconducting parameters for Im-3m-H₃S and Fm-3m- LaH₁₀—the representative members of two families of high-temperature superconducting hydrides.

The Earth’s lowermost mantle displays an important mineralogical transition from perovskite to post-perovskite but the spin state of iron in these phases remains poorly known. Experimental results suggest that iron occurs in the intermediate spin state in both of these phases, which implies that changes in physical properties of the lower mantle must be governed by factors other than spin transitions in iron.

The progress in generating high static pressures in diamond anvil cells opens opportunities for studying novel materials with unusual properties. Here, the authors report a universal high-pressure diamond edge Raman scale up to 500 gigapascals, which does not require an additional pressure sensor.

Metallization of pure hydrogen via overlapping of electronic bands requires high pressure above 3 Mbar. Here the authors study the Ba-H system and discover a unique superhydride BaH₁₂ that contains molecular hydrogen, which demonstrates metallic properties and superconductivity below 1.5 Mbar.

Owing to the energetic nature of N–N bonds, poly-nitrogen compounds are considered promising high energy density materials. Here, the authors synthesize three iron–nitrogen compounds at high pressure, including FeN₄, which features polymeric nitrogen chains of [N₄²⁻]_n units.

The only known compound of sodium and hydrogen is ionic NaH, but theory predicts the existence of polyhydrides at high pressure. Here, the authors report observations of the formation of polyhydrides above 40 GPa and 2000 K, supporting the idea of multicentre bonding in a material with unusual stoichiometry.

Multi-technique synchrotron measurements support the viability of solid FeO-rich structures at Earth’s mantle base. An order-disorder transition identified in the iron defect structure of FeO may lead to unique physical properties in the region.

High pressure experiments may yield materials with unusual combinations of properties, but typically in small amounts and unstable. Here the authors synthesize millimeter-sized samples of metallic, ultraincompressible and very hard rhenium nitride pernitride, recoverable at ambient conditions.

Iron has the ability to adopt different electronic configurations, and transitions in its spin state in the lower mantle can significantly influence mantle properties and dynamics. Experimental results for two lower-mantle perovskite compositions show that the intermediate spin state of iron is stable throughout the bulk of the lower mantle.

The detailed nucleation and growth kinetics and the crystal structure of catalytically relevant CoPt₃/Au, FePt/Au and Pt/Au metal dumbbell nanoparticles have been obtained by in situ synchrotron small- and wide-angle X-ray scattering techniques.

A lanthanum hydride compound at a pressure of around 170 gigapascals is found to exhibit superconductivity with a critical temperature of 250 kelvin.

Subtle anomalies in how the structure of metallic osmium evolves with pressure are detected using powder X-ray diffraction measurements at ultra-high static pressures; the anomaly at 440 gigapascals is attributed to an electronic transition caused by pressure-induced interactions between core electrons.

Ionization of highly compressed ammonia has previously been predicted by computation. Here, the authors provide experimental evidence for this autoionization process at high pressures, showing the transformation of molecular ammonia into ammonium amide.

Superconductivity was recently observed in the binary iron-based compound, FeSe. It is now shown that under pressure, the transition temperature can rise above 36 K. In addition, no static magnetic ordering is observed for this system, contrary to FeAs superconductors.

The physics of NiO under applied pressure has long been debated and the material has been a key contributor to our understanding of Mott insulators and strongly correlated materials more generally. Here, the authors perform high-pressure X-ray diffraction measurements reporting a pressure-induced structural phase transition for NiO, which they suggest is linked with the metal-insulator transition of this system.