Recent advances in the exploration of carbonates have established their high-pressure crystal chemistry as mainly based on carbon in the sp3 configuration. Such carbonates, built upon isolated or vertex-sharing CO 4 4 - tetrahedra, exhibit striking structural diversity. Despite extensive research, synthesis of layered or framework carbonates remained a long-standing challenge. Herein we report on the synthesis and full structural characterization of a novel carbonate, oP32 CaC2O5 (Pna21), obtained at 122 GPa and 2800 K in a laser-heated diamond anvil cell, with a structure based on a vertex-sharing tetrahedral framework. In addition, mP80 CaCO3 (P21/c) was obtained at the same conditions, featuring pyroxene-like chains of vertex-sharing tetrahedra. In contrast to previously reported CaCO3 phases, we propose a novel racemic model based on both clockwise and counter-clockwise helical chirality of the chains. Ab initio calculations support experimental findings and indicate thermodynamic stability of oP32 CaC2O5 and mP80 CaCO3 in the megabar pressure range.

The synthesis of carbonates with novel types of anions is important for geoscience, chemistry, and materials science. Herein, we present the first inorganic tricarbonate salt, K2C3O7, discovered in laser-heated diamond anvil cells at 55(3) and 45(2) GPa. The crystal structure of K2C3O7 was determined in situ by using synchrotron single-crystal X-ray diffraction from a polycrystalline sample. It features nonplanar [C3O7]2- anions, which consist of three corner-sharing planar CO3 groups rotated relative to one another. This anion extends the homologous series of sp2-carbonates: [CO3]2-─[C2O5]2-─[C3O7]2-. Raman spectroscopy establishes the characteristic vibrational fingerprint of the [C3O7]2- anion. Density functional theory (DFT) calculations corroborate the experimental results and suggest a thermodynamic stability of K2C3O7 between 10 and 55 GPa. DFT calculations predict a phase transition between 80 and 90 GPa associated with polymerization of the [C3O7]2- groups, accompanied by a change in the coordination polyhedra of two carbon atoms from triangles to tetrahedra. These results imply that other sp2-and mixed sp2/sp3-carbonates might be stabilized at a high pressure.

Synthesis at extreme conditions enables access to nitrogen-rich carbon-nitrogen anions that cannot be obtained at ambient conditions. Here, through a direct reaction between Eu(N3)2 and EuC2 with Fe in a laser-heated diamond anvil cell (DAC) at 50(3) GPa, we synthesized the first inorganic hydrogen-free pyronitridocarbonate, Eu4Fe x (C2N5)2, x = 0.864(6), featuring novel highly charged [C2N5]7- anions, along with the first stoichiometric oxygen-free rare-earth metal guanidinate Eu5(CN3)3. The crystal structures of both compounds were determined via synchrotron single-crystal X-ray diffraction (SCXRD) and fully corroborated by density functional theory (DFT) calculations. Eu4Fe x (C2N5)2 was found to be recoverable at pressures close to ambient. Keeping the sample at ambient conditions for 1 day leads to splitting of half of the [C2N5]7- units in Eu4Fe x (C2N5)2 into the guanidinate [CN3]5- and carbodiimide [CN2]2- anions. The statistical analysis of the multigrain SCXRD data and DFT-based electronic structure analysis well defined the chemical nature of the bonding in [C2N5]7- and [CN3]5- anions. This study provides a clear synthetic pathway to a new class of inorganic nitridocarbonates.

Recent advances in the exploration of carbonates have established their high-pressure crystal chemistry as mainly based on carbon in the sp 3 configuration. Such carbonates, built upon isolated or vertex-sharing CO44- tetrahedra, exhibit striking structural diversity. Despite extensive research, synthesis of layered or framework carbonates remained a long-standing challenge. Herein we report on the synthesis and full structural characterization of a novel carbonate, oP32 CaC2O5 (Pna2 1), obtained at 122 GPa and 2800 K in a laser-heated diamond anvil cell, with a structure based on a vertex-sharing tetrahedral framework. In addition, mP80 CaCO3 (P2 1 /c) was obtained at the same conditions, featuring pyroxene-like chains of vertex-sharing tetrahedra. In contrast to previously reported CaCO3 phases, we propose a novel racemic model based on both clockwise and counter-clockwise helical chirality of the chains. Ab initio calculations support experimental findings and indicate thermodynamic stability of oP32 CaC2O5 and mP80 CaCO3 in the megabar pressure range.

The phase transition sequences of MeX2 compounds (Me = metal or, more generally, an electropositive element), whose constituent atoms contribute 16 valence electrons per formula unit under high pressure, are of fundamental importance in materials science, high-pressure chemistry, and mineral physics. Here, we report the first observation of trigonal prismatic coordination in this class of materials, realized in magnesium dichloride MgCl2. We synthesized anhydrous MgCl2 by the direct reaction of elemental magnesium with carbon tetrachloride (CCl4) in laser-heated diamond anvil cells from 7(2) to 83(3) GPa. Single-crystal X-ray diffraction identified the known hP3-MgCl2 polymorph at 7(2) GPa, and two previously unknown high-pressure phases: an orthorhombic oP72-MgCl2 at 28(2) and 44(3) GPa, and a cotunnite-type oP12-MgCl2 at 64(3), 73(3), and 83(3) GPa. The oP72 phase features distorted MgCl6 trigonal prisms, while the oP12 phase adopts MgCl8 bicapped trigonal prisms. This sequence of hP3 → oP72 → oP12 reveals a complex pressure-induced structural transition from layered to three-dimensional frameworks. Ab initio calculations agree well with the experimental structural data, support the stability range of the new polymorphs, provide the equation of states, and reveal their electronic properties. Our findings demonstrate several transformation pathways by which MeX2 compounds evolve toward cotunnite-type structures under compression.

The chemical evolution of Earth’s mantle is governed by the interplay between primordial reservoirs formed during accretion and recycled components introduced by subduction. While helium and hydrogen isotopic anomalies strongly suggest the existence of primordial deep-water reservoirs, the mineral hosts capable of sequestering hydrogen during crystallization of basal magma ocean remain elusive. Here we use high-pressure and high-temperature experiments in laser-heated diamond anvil cells and report the synthesis of two hexagonal iron oxyhydroxides, Fe5O12Hx and Fe7O12Hx, under lowermost mantle conditions. We demonstrate that these phases can form under water-undersaturated conditions and exhibit high densities that facilitate gravitational settling. Capable of hosting both primordial and recycled water, these dense oxyhydroxides provide a plausible mineralogical basis for the seismically observed ultralow-velocity zones at the core–mantle boundary. Furthermore, their stability provides a mechanism for the transport of volatiles into Earth’s core or their episodic release into mantle plumes. Therefore, deep mantle iron oxyhydroxides may play a critical role in modulating planetary volatile cycles throughout geological time. Dense iron oxyhydroxide phases may form from an early basal magma ocean, trapping water and potentially contributing to the formation of thermochemical anomalies in the deep mantle, according to high-pressure and high-temperature experiments.

Interactions between carbonates and silicates play a central role in many industrial and planetary processes. Although current knowledge is largely limited to silicate-carbonate exchange mechanisms, high-pressure compounds incorporating both carbonate and silicate units have long been anticipated. Here we report the synthesis of the high-pressure silicate-diorthocarbonate CaSiC2O7 at 122(2) GPa and 2800(200) K. CaSiC2O7 is based on the framework of vertex-sharing SiO6 octahedra and CO4 tetrahedra. Ab initio calculations are consistent with the experimental results and indicate dynamical and mechanical stability of this phase over a wide pressure range. These findings reveal an additional pathway for carbonate-silicate interaction in carbonate-rich deep-mantle environments. CaSiC2O7 has a density lower than that of major mantle minerals and exhibits comparatively low acoustic velocities, suggesting that silicate-carbonates may contribute to seismic anomalies near the core-mantle boundary.

High-pressure synthesis provides unique pathways to materials with unprecedented structures and properties. Here we report the synthesis and structural characterization of novel rare-earth (La, Sm, Gd, Dy) chlorides, chloride carbides, and oxychloride phases obtained due to complex chemical reactions in diamond anvil cells after laser heating of rare-earth metals and NaCl at pressures of 39-127 GPa and temperatures of 2500-2800 K. Synchrotron single-crystal X-ray diffraction analysis allowed us to solve previously unknown crystal structures of binary (La2Cl, LaCl, LaCl3, DyCl) and ternary (DyNa2Cl5, Sm2ClC2, Gd2ClC2, Dy2ClC2, Sm19ClC18, Gd19ClC18, Dy5Cl3C, DyOCl) compounds. Significantly, we identified trans-polyacetylene-like carbon chains in lanthanide chloride carbides, a structural motif previously hypothesized but not observed experimentally. Our findings highlight the enhanced chemical reactivity of alkali halides under extreme conditions, uncovering novel chemical bonding and expanding the landscape of potential functional materials accessible through high-pressure synthesis.

We present an approach to nanoscale-resolution high-sensitivity imaging of internal material structure under in situ/operando conditions for virtually any sample environment. When bulky or heavy sample environment is required state-of-the-art X-ray imaging techniques, such as scanning and full-field microscopy or holography fail to deliver high-resolution imaging capabilities due to either i) extremely small optics' working distance for magnification-based methods or ii) the inability to precisely control heavy sample position in the case of lens-less methods. In this work, we address those challenges for a scanning lens-less imaging method called ptychography. Instead of precisely controlling the sample position during raster scan in a focused, confined X-ray beam, we are scanning that beam across the sample. This overcomes the constraints on scanning procedure imposed by sample size/weight and delivers unmatched scanning speed while maintaining high precision of beam position during the scan. We directly applied our approach, showcasing phase contrast nanoimaging with diamond anvil cells, and visualized intricate details of the melting and oxidation of laser-irradiated iron under pressure of 50 GPa.

Zusammenfassung Die Entdeckung und Stabilisierung des cyclo ‐N 5 ⁻ Anions hat eine neue Klasse von Pentazolatverbindungen eingeführt, die ein großes Potential als neuartige Materialien mit hoher Energiedichte pro Formeleinheit aufweisen. Dieses Potential kann im Weiteren durch Erhöhung des Pentazolat‐zu‐Metall‐Verhältnisses verbessert werden. Wir berichten in dieser Publikation von einer Hochdruck‐ und Hochtemperatursynthese zur Darstellung eines neuartigen Yttrium‐Pentazolat, Y(N 5 ) 3 ·N 2 , das ein außerordentlich großes Stickstoff‐zu‐Metall‐Verhältnis von 17:1 aufweist. Die Synthese von Y(N 5 ) 3 ·N 2 erfolgte ausgehend von elementarem Yttrium und Stickstoff durch laserinduziertes Heizen bei 3000 K und bei einem Druck von 125 GPa in einer Diamantstempelzelle. Die Kristallstruktur, die ein dreidimensionales Metallpentazolat‐Gerüst mit Stickstoffeinschlüssen aufweist, wurde durch in‐situ Synchrotron‐Einkristall‐Röntgenbeugung gelöst und verfeinert. Diese Struktur weist eine perowskitartige Topologie auf, wo die Pentazolatringe vereinfacht als eckenverknüpfte Oktaeder angesehen werden können, wo sich neutrale Stickstoffdimere in den Zentren der aufgespannten Oktaederlücken einlagern, während Yttriumatome verzerrte Kuboktaeder innerhalb des oktaedrischen 3D‐Rahmens besetzen. Theoretische Rechnungen mittels Dichtefunktionaltheorie bestätigen die experimentellen Ergebnisse und liefern weitere Einblicke in die Stabilität und Eigenschaften der synthetisierten Verbindung. Y(N 5 ) 3 ·N 2 ist das erste Beispiel für die Stabilisierung von drei Pentazolat‐Anionen pro Metallkation und übertrifft damit das zuvor erreichte Verhältnis von 1:1. Darüber hinaus schlagen wir eine neue Methode zur Strukturklassifizierung lösungsmittelfreier anorganischer Pentazolate vor, die auf der räumlichen Anordnung ihrer strukturellen Baueinheiten basiert und einen wichtigen Schritt für die systematische Einordnung von Pentazolaten sowie anderen Polynitriden darstellt.

Since the pioneering works of Peierls, one-dimensional materials have attracted great attention. Still, the synthesis of truly monoatomic chains remains elusive. In this study, we explore a novel path of experimental synthesis of monoatomic one-dimensional chains by their chemical stabilization in ionic compounds. We demonstrate that in synthesized at high pressure sodium halides Na4X5 (X = I, Br, Cl) with hP18 Ga4Ti5-type structures, transfer of valence electrons from cations to anions leads to the formation of halogen chains connected with other atoms only by ionic interaction and having one-dimensional electronic structure. The Peierls physics in the systems is confirmed by theoretical calculations, newly synthesized incommensurately modulated i-hP18-Na4X5 (X = I, Br, Cl) compounds, as well as by the discovered hP36 phases of Na4Cl5 and Na4Br5.

Seismic, geodetic and cosmochemical evidence point to Mars having a sulfur-rich liquid core. Due to the similarity between estimates of the core's sulfur content and the iron-iron sulfide eutectic composition at core conditions, it has been concluded that temperatures are too high for Mars to have an inner core. Recent low density estimates for the core, however, appear consistent with sulfur contents that are higher than the eutectic composition, leading to the possibility that an inner core could form from a high-pressure iron sulfide phase. Here we report the crystal structure of a phase with the formula Fe4+xS3, the iron content of which increases with temperature, approaching the stoichiometry Fe5S3 under Martian inner core conditions. We show that Fe4+xS3 has a higher density than the liquid Martian core and that a Fe4+xS3 inner core would crystalize if temperatures fall below 1960 (±105) K at the center of Mars.

Recent advances in the exploration of carbonates have established their high-pressure crystal chemistry as mainly based on carbon in the sp 3 configuration. Such carbonates, built upon isolated or vertex-sharing \(\:{\text{C}\text{O}}_{4}^{4-}\) tetrahedra, reveal striking structural diversity. Despite extensive research, synthesis of layered or framework carbonates remained a long-standing challenge. Herein we report on the synthesis and full structural characterization of a novel carbonate, oP32 CaC 2 O 5 , obtained at 122 GPa and 2800 K in a laser-heated diamond anvil cell. Crystal structure of oP32 CaC 2 O 5 based on a vertex-sharing tetrahedral framework. In addition, mP80 CaCO 3 was obtained at the same conditions, featuring pyroxene-like chains of vertex-sharing tetrahedra. In contrast to previously reported experimentally observed or theoretically proposed CaCO 3 phases, our single crystal X-ray diffraction data reveal that the structure of mP80 CaCO 3 features both clockwise and counter-clockwise helical chirality of the pyroxene-like chains. Ab initio calculations support experimental findings and indicate thermodynamic stability of oP32 CaC 2 O 5 and mP80 CaCO 3 in the megabar pressure range.

The discovery and stabilization of the cyclo-N 5 ⁻ anion have introduced a class of pentazolate compounds with significant potential as high-energy-density materials (HEDMs). This potential could be further enhanced by increasing the pentazolate-to-metal ratio. Here, we report the high-pressure, high-temperature synthesis and characterization of a novel yttrium pentazolate, Y(N 5 ) 3 ·N 2 , which exhibits an exceptionally high nitrogen-to-metal ratio of 17:1. Y(N 5 ) 3 ·N 2 was synthesized from yttrium and nitrogen by laser heating to 3000 K at 125 GPa in a diamond anvil cell. Its crystal structure, a 3D nitrogen-inclusion metal-pentazolate framework, was solved and refined in situ using synchrotron single-crystal X-ray diffraction. This structure demonstrates a perovskite topology, as pentazolate ring centers form octahedra connected via vertices, neutral nitrogen dimers are located at the centers of the octahedra, and yttrium atoms occupy distorted cuboctahedra within the octahedral 3D framework. Density functional theory (DFT) calculations corroborate the experimental findings and provide further insights into the stability and properties of the synthesized compound. Y(N 5 ) 3 ·N 2 is the first example of stabilizing three pentazolate anions per metal cation, surpassing the previously achieved 1:1 ratio. Additionally, we propose a centroid-based structure typification for solvent-free inorganic pentazolates, serving as an important step for further structural classification of pentazolates and other polynitrides.

Polar metals have attracted growing interest due to both their significance in fundamental science and their potential functionalities. Here, we report the discovery of a novel polar metal, magnesium chloride Mg3Cl7, in which the metallicity of the polar structure is uniquely driven by attractive halogen interactions. Mg3Cl7 was synthesized in laser-heated diamond anvil cells and observed at pressures of 28(2)-93(3) GPa. Synchrotron single-crystal X-ray diffraction revealed that the structure of the new compound has polar hexagonal space group P63mc, representing an example of a previously unknown anti-Th7Fe3 structure type. Measurements of the physical properties have shown that the material is a metallic conductor capable of emitting second-harmonic generation light. Ab initio calculations support experimental findings and reveal complex halogen-halogen interactions, anionic metallicity, anisotropic electronic structure, and the presence of Dirac and Weyl points at the Fermi level. Our findings broaden the family of polar metals, provide new insight into halogen bonding under extreme conditions, and offer a platform for further exploration of materials' unconventional electronic behavior.

Two novel ternary compounds, yttrium borate oC20-YBO3 and yttrium orthocarbonate hR39-Y3(CO4)2, were synthesized at 90 and 120 GPa upon heating to about 3500 K in a laser-heated diamond anvil cell. Their crystal structures were solved and refined using in situ high-pressure synchrotron single-crystal X-ray diffraction. The crystal structure of oC20-YBO3 features previously unobserved infinite unbranched zigzag chains of corner-sharing BO4 tetrahedra. The compound hR39-Y3(CO4)2 consists of isolated [CO4]4- orthocarbonate anions and represents the first rare-earth orthocarbonate. Density functional theory calculations reproduce the structures of the new compounds and provide further insight into their stability and physical properties. Our results enrich the chemistry of metal borates and carbonates.

Recently, we discovered the aluminium oxonitridoborate AlB 4 O 6 N:Cr 3+ , whose high-pressure/high-temperature synthesis could be optimized in the last months. This compound shows extraordinary luminescence properties, that closely resemble the famous compound ruby, whose luminescence is characterized by two narrow R emission lines close to each other. Apart from a slight blue shift, the main difference of the luminescence of the title compound is the presence of a single R line due to nearly perfect [(Al/Cr)O 6 ] octahedra in the structure. Ruby plays a crucial role as gold standard for pressure calibration in diamond anvil cells by measuring the shift of one of these R lines with increasing pressure. However, the accuracy is limited at elevated pressure, since the two R lines broaden and eventually merge. Since the compound AlB 4 O 6 N:Cr 3+ showed only one single R line up to a pressure of at least 52 GPa, it could provide improved accuracy for the calibration of diamond anvil cells. This raises the question as to how the material behaves at even higher pressures. Therefore, we performed luminescence measurements of AlB 4 O 6 N:Cr 3+ up to 78(1) GPa in a diamond anvil cell and complemented our findings with single-crystal diffraction data (synchrotron) at elevated pressure to detect possible structural changes.