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Under high pressure, elemental sulfur shows a sharp density discontinuity that evolves with pressure and temperature and terminates at a critical point, indicating a first-order liquid–liquid phase transition.

The nature and stability of carbon dioxide under extreme conditions relevant to the Earth’s mantle is still under debate, in view of its possible role within the deep carbon cycle. Here, the authors perform high-pressure experiments providing evidence that polymeric crystalline CO₂ is stable under megabaric conditions.

Chemical elements at high pressure may behave more consistently with their periodic properties than they do at ambient conditions. The authors report the synthesis of PH₃ from black phosphorous and hydrogen, and the crystallization of the van der Waals compound (PH₃)₂H₂ which fills a gap in the chemistry of adjacent elements in the periodic table.

Iron in partially molten rocks under deep-mantle conditions partitions into the melt phase less than previously reported, suggesting that melt generated near the core–mantle boundary should segregate upwards.

The absence of very deep moonquakes implies that the lower mantle of the Moon is partially molten. An analysis of the density range of lunar melts at high pressures suggests that only titanium-rich melt is neutrally buoyant deep within the Moon.

Supervolcano eruptions dwarf all historical eruptions, but their trigger mechanisms are unclear. Experimental measurements of magma density at high pressures and temperatures show that the buoyancy of magma alone can impose sufficient pressure at the roof of a supervolcano magma chamber to induce an eruption.

Carbonate mineral aqueous solubility decreases as carbonates become more Mg-rich during subduction. Coupled with regional variations in amounts of carbon and water subducted, this explains discrepancies in estimates of carbon recycling, suggesting that only around a third returns to the surface.

Extreme static pressures exceeding a million atmospheres exist in a variety of natural environments, but obtaining such pressures in a laboratory is still a challenge. Here, the authors develop a toroidal diamond anvil design that allows for the generation of 600 GPa (6 million atmospheres) in routinely used diamond anvil cells.

The presence of α-seifertite and seiferite in shocked meteorites are used to determine shock pressures. Here, using high-pressure experiments, the authors find that the presence of α-cristobalite does not exclude high-pressure transformation and seifertite does not necessarily indicate high pressures.

The reactivity of the noble gases—a notoriously inert group—at high pressures is intriguing. Now, two xenon oxides with unusual stoichiometries, Xe₂O₅ and Xe₃O₂, have been synthesized above 78 GPa and predicted to be stable above 50 GPa, indicating that xenon is more reactive than previously thought.

Carbonates are shown to exist in the lower mantle as seen in diamond inclusions, but thermodynamic constraints are poorly understood. Here, the authors synthesise two new iron carbonate compounds and find that self-oxidation-reduction reactions can preserve carbonates in the mantle.

Carbonates are transported into the deep Earth by subduction of the oceanic lithosphere, but the stability fields of subducted carbonates as a function of pressure, temperature, and composition remain incompletely described. Here, the authors synthesize the anhydrous, mixed pyrocarbonate Ca3[C2O5]2[CO3] from Ca[CO3] and CO2 in a laser-heated diamond anvil cell at moderate pressure and elucidate its structural features.

Structural studies of pyrene, a polycyclic aromatic hydrocarbon, have so far been limited to below 2 GPa. Here, studying the crystal structure of pyrene up to ~35 GPa using in situ single-crystal synchrotron X-ray diffraction in diamond anvil cells, the authors discover two previously unobserved polymorphs, and find that gradual compression results in continuous compaction of molecular packing, eventually leading to a curvature of the molecules.

The transition metal dichalcogenide IrTe₂ is a candidate system to realise topological superconductivity, a sought-after state which could host Majorana fermions, and hence is of interest to the field of quantum computing. Here, the authors combine high-pressure X-ray diffraction and DFT calculations to investigate the evolution in the crystal- and electronic structure of IrTe₂ as a function of pressure, highlighting the role of the Te-Ir-Te bond angle.

The study of materials under extreme conditions can reveal interesting physics in diverse areas such as condensed matter and geophysics. Here, the authors investigate experimentally and theoretically the high pressure-high temperature phase diagram of niobium revealing a previously unobserved phase transition from body-centered cubic to orthorhombic phase.

X-ray science at modern Synchrotrons and X-ray Free Electron Laser facilities are enabling the study of subtle structural changes of matter from the single atom to the macroscopic scale. This paper reviews new concepts in synchrotron storage rings design and reports on the successful commissioning and operation of the new X-ray storage ring of the European Synchrotron Radiation Facility (ESRF) in Grenoble.