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Beryllium in inorganic compounds is usually coordinated to four oxygen atoms, but higher coordination numbers have been predicted. Here the authors observe a pressure induced stepwise transition in CaBe₂P₂O₈ where Be coordination changes to trigonal-bipyramidal and octahedral, implying that d orbitals are not mandatory for high coordination.

The planar hexazine dianion ring (N₆^2–), which had previously been predicted to exist, has now been synthesized from potassium azide (KN₃) under laser heating in a diamond anvil cell above 45 GPa; it remains metastable down to 20 GPa. By contrast, at 30 GPa an unusual N₂-containing compound with the formula K₃(N₂)₄ was produced.

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.

The authors demonstrate that carbides with infinite chains of fused [C6] and [C5] rings are synthesized at deep planetary pressures and temperatures. Hydrolysis of these carbides may lead to polycyclic aromatic hydrocarbons in the Universe.

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.

The authors use systematic monitoring across the former USSR to investigate phenological changes across taxa. The long-term mean temperature of a site emerged as a strong predictor of phenological change, with further imprints of trophic level, event timing, site, year and biotic interactions.

Experiments using high-intensity X-ray pulses incident on high-pressure hydrocarbons suggest that diamond formation can occur at shallower depths in icy planets and may play a role in the internal convection that generates their magnetic fields.

Feldspars are stable at pressures up to 3 GPa along the mantle geotherm, but they can persist metastably at higher pressures at colder conditions. Here, above 10 GPa the authors find  new high-pressure polymorphs of feldspars that could persist at depths corresponding to the Earth’s upper mantle, potentially influencing the dynamics and fate of cold subducting slabs.

The chemical stability of alkali halides has caused them to be exploited as inert media in high-pressure, high-temperature experiments. Here, NaCl and KCl are unexpectedly found to react with yttrium, dysprosium and iron oxide in a laser-heated diamond anvil cell, producing Y₂Cl, DyCl, Y₂ClC and Dy₂ClC at ~40 GPa and 2000 K and FeCl₂ at ~160 GPa and 2100 K.

Polynitrogen compounds are potentially promising high energy density materials, but are difficult to synthesize due to their instability. Here, the authors observe the formation, under high pressure, of a Mg₂N₄ magnesium–tetranitrogen salt which remains stable at ambient conditions.

The lowermost mantle and transition zone are increasingly oxidized at depth, according to analyses of the oxidation state of iron in majoritic garnet inclusions from deep diamonds.

Phase transitions in materials are intriguing, and can also be of practical importance. Below ∼150 K, mixed-valent iron oxide Fe₄O₅ has now been shown to undergo an unusual charge-ordering phase transition that involves the competing formation of iron dimers and trimers, and leads to a significant increase in electrical resistivity.

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.

The charge order transition of commonly known magnetite has only recently been unraveled. Here, the measurement of the low-temperature high-pressure phase diagram of a related material (Fe₄O₅) elucidates the interplay of average oxidation state and charge-ordering phenomena in the iron oxide family.

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.

This work concerns a systematic study of Fe_1-xO employing complementary methods of powder and single-crystal X-ray diffraction and synchrotron Mössbauer source spectroscopy up to 94 GPa and 1700 K. It presents a structural and magnetic transitional pressure-temperature diagram of Fe_1-xO and demonstrates the complex physicochemical properties of simple Fe_1-xO binary oxide under extreme conditions.