On the identification of hyperhydrated sodium chloride hydrates, stable at icy moon conditions.

Sodium chloride is expected to be found on many of the surfaces of icy moons like Europa and Ganymede. However, spectral identification remains elusive as the known NaCl-bearing phases cannot match current observations, which require higher number of water of hydration. Working at relevant conditions for icy worlds, we report the characterization of three "hyperhydrated" sodium chloride (SC) hydrates, and refined two crystal structures [2NaCl·17H2O (SC8.5); NaCl·13H2O (SC13)]. We found that the dissociation of Na+ and Cl- ions within these crystal lattices allows for the high incorporation of water molecules and thus explain their hyperhydration. This finding suggests that a great diversity of hyperhydrated crystalline phases of common salts might be found at similar conditions. Thermodynamic constraints indicate that SC8.5 is stable at room pressure below 235 K, and it could be the most abundant NaCl hydrate on icy moon surfaces like Europa, Titan, Ganymede, Callisto, Enceladus, or Ceres. The finding of these hyperhydrated structures represents a major update to the H2O-NaCl phase diagram. These hyperhydrated structures provide an explanation for the mismatch between the remote observations of the surface of Europa and Ganymede and previously available data on NaCl solids. It also underlines the urgent need for mineralogical exploration and spectral data on hyperhydrates at relevant conditions to help future icy world exploration by space missions.

Superior Superconducting Properties Realized in Quaternary La-Y-Ce Hydrides at Moderate Pressures.

The recent revolution in the superconductivity field stems from hydride superconductors. Multicomponent hydrides provide a crucial platform for tracking high-temperature superconductors. Besides high superconducting transition temperature (Tc), achieving both giant upper critical magnetic field [µ0Hc2(0)] and high critical current density [Jc(0)] is also key to the latent potential of the application for hydride superconductors. In this work, we have successfully synthesized quaternary La-Y-Ce hydrides with excellent properties under moderate pressure by using the concept of "entropy engineering." The obtained temperature dependence of the resistance provides evidence for the superconductivity of Fm3m-(La,Y,Ce)H10, with the maximum Tc ∼ 190 K (at 112 GPa). Notably, Fm3m-(La,Y,Ce)H10 boasts exceptional properties: µ0Hc2(0) reaching 292 T and Jc(0) surpassing 4.61 × 107 A/cm2. Compared with the binary LaH10/YH10, we find that the Fm3m structure in (La,Y,Ce)H10 can be stable at relatively low pressures (112 GPa). These results indicate that multicomponent hydrides can significantly enhance the superconducting properties and regulate stabilizing pressure through the application of "entropy engineering." This work stimulates the experimental exploration of multihydride superconductors and also provides a reference for the search of room-temperature superconductors in more diversified hydride materials in the future.

High-Pressure oC16-YBr3 Polymorph Recoverable to Ambient Conditions: From 3D Framework to Layered Material.

Exfoliation of graphite and the discovery of the unique properties of graphene─graphite's single layer─have raised significant attention to layered compounds as potential precursors to 2D materials with applications in optoelectronics, spintronics, sensors, and solar cells. In this work, a new orthorhombic polymorph of yttrium bromide, oC16-YBr3 was synthesized from yttrium and CBr4 in a laser-heated diamond anvil cell at 45 GPa and 3000 K. The structure of oC16-YBr3 was solved and refined using in situ synchrotron single-crystal X-ray diffraction. At high pressure, it can be described as a 3D framework of YBr9 polyhedra, but upon decompression below 15 GPa, the structure motif changes to layered, with layers comprising edge-sharing YBr8 polyhedra weakly bonded by van der Waals interactions. The layered oC16-YBr3 material can be recovered to ambient conditions, and according to Perdew-Burke-Ernzerhof-density functional theory calculations, it exhibits semiconductor properties with a band gap that is highly sensitive to pressure. This polymorph possesses a low exfoliation energy of 0.30 J/m2. Our results expand the list of layered trivalent rare-earth metal halides and provide insights into how high pressure alters their structural motifs and physical properties.

High temperature decomposition of polymeric carbon monoxide at pressures up to 120 GPa.

While polymeric carbon monoxide (pCO) has been experimentally found to remain amorphous and undecomposed at room temperature up to 50 GPa, the question of whether crystalline counterparts of it can be obtained naturally raises. From different computational studies, it can be inferred that either the crystallization of amorphous pCO (a-pCO) or its decomposition into a mixture of CxOy suboxides (x > y) or carbon and CO2 may occur. In this study, we report experimental investigations of the high temperature (700-4000 K) transformation of a-pCO in the 47-120 GPa pressure range, conducted by x-ray diffraction in laser heated diamond anvil cells. Our results show the formation of no crystalline phases other than CO2 phase V, thus indicating the decomposition of the pristine a-pCO into CO2 and, likely, a mixture of amorphous CxOy suboxides and amorphous carbon hardly detectable at extreme conditions. These results support the theoretical picture of the pCO decomposition. We also show that the pressure-temperature kinetic border for this decomposition is very steep, thus indicating a strongly pressure-dependent kinetic barrier.

Unconventional Route to High-Pressure and -Temperature Synthesis of GeSn Solid Solutions.

Ge and Sn are unreactive at ambient conditions. Their significant promise for optoelectronic applications is thus largely confined to thin film investigations. We sought to remove barriers to reactivity here by accessing a unique pressure, 10 GPa, where the two elements can adopt the same crystal structure (tetragonal, I41/amd) and exhibit compatible atomic radii. The route to GeSn solid solution, however, even under these directed conditions, is different. Reaction upon heating at 10 GPa occurs between unlike crystal structures (Ge, Fd3m and Sn, I4/mmm), which also have highly incompatible atomic radii. They should not react, but they do. A reconstructive transformation of I4/mmm into the I41/amd solid solution then follows. The new tetragonal GeSn solid solution (I41/amd a = 5.280(1) Å, c = 2.915(1) Å, Z = 4 at 9.9 GPa and 298 K) also constitutes the structural and electronic bridge between 4-fold and newly prepared 8-fold coordinated alloy cubic symmetries. Furthermore, using this high-pressure route, bulk cubic diamond-structured GeSn alloys can now be obtained at ambient pressure. The findings here remove confining conventional criteria on routes to synthesis. This opens innovative avenues to advanced materials development.

Laser heating system at the Extreme Conditions Beamline, P02.2, PETRA III.

A laser heating system for samples confined in diamond anvil cells paired with in situ X-ray diffraction measurements at the Extreme Conditions Beamline of PETRA III is presented. The system features two independent laser configurations (on-axis and off-axis of the X-ray path) allowing for a broad range of experiments using different designs of diamond anvil cells. The power of the continuous laser source can be modulated for use in various pulsed laser heating or flash heating applications. An example of such an application is illustrated here on the melting curve of iron at megabar pressures. The optical path of the spectroradiometry measurements is simulated with ray-tracing methods in order to assess the level of present aberrations in the system and the results are compared with other systems, that are using simpler lens optics. Based on the ray-tracing the choice of the first achromatic lens and other aspects for accurate temperature measurements are evaluated.

Polymorphs of the Gadolinite-Type Borates ZrB2 O5 and HfB2 O5 Under Extreme Pressure.

Based on the results from previous high-pressure experiments on the gadolinite-type mineral datolite, CaBSiO4 (OH), the behavior of the isostructural borates ß-HfB2 O5 and ß-ZrB2 O5 have been studied by synchrotron-based in situ high-pressure single-crystal X-ray diffraction experiments. On compression to 120 GPa, both borate layer-structures are preserved. Additionally, at ≈114 GPa, the formation of a second phase can be observed in both compounds. The new high-pressure modification γ-ZrB2 O5 features a rearrangement of the corner-sharing BO4 tetrahedra, while still maintaining the four- and eight-membered rings. The new phase γ-HfB2 O5 contains ten-membered rings including the rare structural motif of edge-sharing BO4 tetrahedra with exceptionally short B-O and B⋅⋅⋅B distances. For both structures, unusually high coordination numbers are found for the transition metal cations, with ninefold coordinated Hf4+ , and tenfold coordinated Zr4+ , respectively. These findings remarkably show the potential of cold compression as a low-energy pathway to discover metastable structures that exhibit new coordinations and structural motifs.

An Unexpected Cubic Symmetry in Group†IV Alloys Prepared Using Pressure and Temperature.

The cubic diamond (Fd 3 ‾ m) group IVA element Si has been the material driver of the electronics industry since its inception. We report synthesis of a new cubic (Im 3 ‾ m) group IVA material, a GeSn solid solution, upon heating Ge and Sn at pressures from 13 to 28 GPa using double-sided diamond anvil laser-heating and large volume press methods. Both methods were coupled with in situ angle dispersive X-ray diffraction characterization. The new material substantially enriches the seminal group IVA alloy materials landscape by introducing an eightfold coordinated cubic symmetry, which markedly expands on the conventional tetrahedrally coordinated cubic one. This cubic solid solution is formed, despite Ge never adopting the Im 3 ‾ m symmetry, melting inhibiting subsequent Im 3 ‾ m formation and reactant Ge and Sn having unlike crystal structures and atomic radii at all these pressures. This is hence achieved without adherence to conventional formation criteria and routes to synthesis. This advance creates fertile avenues for new materials development.

High-Pressure Polymeric Nitrogen Allotrope with the Black Phosphorus Structure.

Studies of polynitrogen phases are of great interest for fundamental science and for the design of novel high energy density materials. Laser heating of pure nitrogen at 140 GPa in a diamond anvil cell led to the synthesis of a polymeric nitrogen allotrope with the black phosphorus structure, bp-N. The structure was identified in situ using synchrotron single-crystal x-ray diffraction and further studied by Raman spectroscopy and density functional theory calculations. The discovery of bp-N brings nitrogen in line with heavier pnictogen elements, resolves incongruities regarding polymeric nitrogen phases and provides insights into polynitrogen arrangements at extreme densities.

Nitride Spinel: An Ultraincompressible High-Pressure Form of BeP2 N4.

Owing to its outstanding elastic properties, the nitride spinel γ-Si3 N4 is of considered interest for materials scientists and chemists. DFT calculations suggest that Si3 N4 -analog beryllium phosphorus nitride BeP2 N4 adopts the spinel structure at elevated pressures as well and shows outstanding elastic properties. Herein, we investigate phenakite-type BeP2 N4 by single-crystal synchrotron X-ray diffraction and report the phase transition into the spinel-type phase at 47 GPa and 1800 K in a laser-heated diamond anvil cell. The structure of spinel-type BeP2 N4 was refined from pressure-dependent in situ synchrotron powder X-ray diffraction measurements down to ambient pressure, which proves spinel-type BeP2 N4 a quenchable and metastable phase at ambient conditions. Its isothermal bulk modulus was determined to 325(8) GPa from equation of state, which indicates that spinel-type BeP2 N4 is an ultraincompressible material.

Assessment and Management of HIV Distal Sensory Peripheral Neuropathy: Understanding the Symptoms.

Distal sensory peripheral neuropathy (HIV-DSP) affects upwards of 50% of people living with HIV. Causing often debilitating symptoms of tingling, numbness and burning, HIV-DSP can result in disability, unemployment and low quality of life. Comorbidities further complicate nursing care, heightening risk of polypharmacy and symptom exacerbation. Therefore, a neurological sensory assessment, combined with the patient's self-report of symptoms, can help nurse practitioners visualize, quantify and understand symptoms. Common pharmacological interventions include antiepileptics, antidepressants, analgesics and medical marijuana. The complexity of care for individuals with HIV-DSP merits a comprehensive approach. Implications for practice include interdisciplinary management with neurologists, podiatrists, mental health providers, and nurse-led counseling inclusive of patient safety teaching.

Boron Phosphorus Nitride at Extremes: PN6 Octahedra in the High-Pressure Polymorph ß-BP3 N6.

The high-pressure behavior of non-metal nitrides is of special interest for inorganic and theoretical chemistry as well as materials science, as these compounds feature intriguing elastic properties. The double nitride α-BP3 N6 was investigated by in situ single-crystal X-ray diffraction (XRD) upon cold compression to a maximum pressure of about 42 GPa, and its isothermal bulk modulus at ambient conditions was determined to be 146(6) GPa. At maximum pressure the sample was laser-heated, which resulted in the formation of an unprecedented high-pressure polymorph, ß-BP3 N6 . Its structure was elucidated by single-crystal XRD, and can be described as a decoration of a distorted hexagonal close packing of N with B in tetrahedral and P in octahedral voids. Hence, ß-BP3 N6 is the first nitride to contain PN6 octahedra, representing the much sought-after proof of principle for sixfold N-coordinated P that has been predicted for numerous high-pressure phases of nitrides.

Structural and Magnetic Transitions in CaCo3V4O12 Perovskite at Extreme Conditions.

We investigated the structural, vibrational, magnetic, and electronic properties of the recently synthesized CaCo3V4O12 double perovskite with the high-spin (HS) Co2+ ions in a square-planar oxygen coordination at extreme conditions of high pressures and low temperatures. The single-crystal X-ray diffraction and Raman spectroscopy studies up to 60 GPa showed a conservation of its cubic crystal structure but indicated a crossover near 30 GPa. Above 30 GPa, we observed both an abnormally high "compressibility" of the Co-O bonds in the square-planar oxygen coordination and a huge anisotropic displacement of HS-Co2+ ions in the direction perpendicular to the oxygen planes. Although this effect is reminiscent of a continuous HS → LS transformation of the Co2+ ions, it did not result in the anticipated shrinkage of the cell volume because of a certain "stiffing" of the bonds of the Ca and V cations. We verified that the oxidation states of all the cations did not change across this crossover, and hence, no charge-transfer effects were involved. Consequently, we proposed that CaCo3V4O12 could undergo a phase transition at which the large HS-Co2+ ions were pushed out of the oxygen planes because of lattice compression. The antiferromagnetic transition in CaCo3V4O12 at 100 K was investigated by neutron powder diffraction at ambient pressure. We established that the magnetic moments of the Co2+ ions were aligned along one of the cubic axes, and the magnetic structure had a 2-fold periodicity along this axis, compared to the crystallographic one.

Diverse high-pressure chemistry in Y-NH3BH3 and Y-paraffin oil systems.

The yttrium-hydrogen system has gained attention because of near-ambient temperature superconductivity reports in yttrium hydrides at high pressures. We conducted a study using synchrotron single-crystal x-ray diffraction (SCXRD) at 87 to 171 GPa, resulting in the discovery of known (two YH3 phases) and five previously unknown yttrium hydrides. These were synthesized in diamond anvil cells by laser heating yttrium with hydrogen-rich precursors-ammonia borane or paraffin oil. The arrangements of yttrium atoms in the crystal structures of new phases were determined on the basis of SCXRD, and the hydrogen content estimations based on empirical relations and ab initio calculations revealed the following compounds: Y3H11, Y2H9, Y4H23, Y13H75, and Y4H25. The study also uncovered a carbide (YC2) and two yttrium allotropes. Complex phase diversity, variable hydrogen content in yttrium hydrides, and their metallic nature, as revealed by ab initio calculations, underline the challenges in identifying superconducting phases and understanding electronic transitions in high-pressure synthesized materials.

Host-Guest Hydrogen Bonding in High-Pressure Acetone Clathrate Hydrates: In Situ Single-Crystal X-ray Diffraction Study.

The phenomenon of host-guest hydrogen bonding in clathrate hydrate crystal structures and its effect on physical and chemical properties have become subjects of extensive research. Hydrogen bonding has been studied for cubic (sI and sII) and hexagonal (sH) binary clathrates, while it has not been addressed for clathrate structures that exist at elevated pressures. Here, four acetone hydrate clathrates have been grown at high-pressure and low-temperature conditions. In situ single-crystal X-ray diffraction revealed that the synthesized phases possess already known trigonal (sTr), orthorhombic (sO), and tetragonal (sT) crystal structures as well as a previously unknown orthorhombic structure, so-called sO-II. Only sO and sII have previously been reported for acetone clathrates. Structural analysis suggests that acetone oxygens are hydrogen-bonded to the closest water oxygens of the host frameworks. Our discoveries show that clathrate hydrates hosting polar molecules are not as exotic as previously thought and could be stabilized at high-pressure conditions through hydrogen bonding.

Polymorphism of feldspars above 10 GPa.

Feldspars are rock-forming minerals that make up most of the Earth's crust. Along the mantle geotherm, feldspars are stable at pressures up to 3 GPa and may persist metastably at higher pressures under cold conditions. Previous structural studies of feldspars are limited to ~10 GPa, and have shown that the dominant mechanism of pressure-induced deformation is the tilting of AlO4 and SiO4 tetrahedra in a tetrahedral framework. Herein, based on results of in situ single-crystal X-ray diffraction studies up to 27 GPa, we report the discovery of new high-pressure polymorphs of the feldspars anorthite (CaSi2Al2O8), albite (NaAlSi3O8), and microcline (KAlSi3O8). The phase transitions are induced by severe tetrahedral distortions, resulting in an increase in the Al and/or Si coordination number. High-pressure phases derived from feldspars could persist at depths corresponding to the Earth upper mantle and could possibly influence the dynamics and fate of cold subducting slabs.

Tricaesium dimolybdate(VI) bromide.

The title compound, Cs(3)(Mo(2)O(7))Br, was synthesized by the reaction of CsNO(3), MoO(3) and 1-ethyl-3-methyl-imidazolium bromide. Its crystal structure is isotypic with K(3)(Mo(2)O(7))Br and contains (MoO(4))(2-) tetra-hedra which share an O atom to produce a [Mo(2)O(7)](2-) dimolybdate(VI) anion with a linear bridging angle and m2 symmetry. The anions are linked by Cs atoms (site symmetry m2), forming sheets parallel to (001). Br atoms (site symmetry m2) are also part of this layer. Another type of Cs atom (3m site symmetry) is located in the inter-layer space and connects the layers via Cs-O and Cs-Br inter-actions into a three-dimensional array.

High pressure phase transitions of paracelsian BaAl2Si2O8.

Three new polymorphs of aluminosilicate paracelsian, BaAl2Si2O8, have been discovered using synchrotron-based in situ high-pressure single crystal X-ray diffraction. The first isosymmetric phase transition (from paracelsian-I to paracelsian-II) occurs between 3 and 6 GPa. The phase transition is associated with the formation of pentacoordinated Al3+ and Si4+ ions, which occurs in a stepwise fashion by sequential formation of Al-O and Si-O bonds additional to those in AlO4 and SiO4 tetrahedra, respectively. The next phase transition occurs between 25 and 28 GPa and is accompanied by the symmetry change from monoclinic (P21/c) to orthorhombic (Pna21). The structure of paracelsian-III consists of SiO6 octahedra, AlO6 octahedra and distorted AlO4 tetrahedra, i.e. the transition is reconstructive and associated with the changes of Si4+ and Al3+ coordination, which show rather complex behaviour with the general tendency towards increasing coordination numbers. The third phase transition is observed between 28 and 32 GPa and results in the symmetry decreasing from Pna21 to Pn. The transition has a displacive character. In the course of the phase transformation pathway up to 32 GPa, the structure of polymorphs becomes denser: paracelsian-II is based upon elements of cubic and hexagonal close-packing arrangements of large O2- and Ba2+ ions, whereas, in the crystal structure of paracelsian-III and IV, this arrangement corresponds to 9-layer closest-packing with the layer sequence ABACACBCB.

Penta- and hexa-coordinated beryllium and phosphorus in high-pressure modifications of CaBe2P2O8.

Beryllium oxides have been extensively studied due to their unique chemical properties and important technological applications. Typically, in inorganic compounds beryllium is tetrahedrally coordinated by oxygen atoms. Herein based on results of in situ single crystal X-ray diffraction studies and ab initio calculations we report on the high-pressure behavior of CaBe2P2O8, to the best of our knowledge the first compound showing a step-wise transition of Be coordination from tetrahedral (4) to octahedral (6) through trigonal bipyramidal (5). It is remarkable that the same transformation route is observed for phosphorus. Our theoretical analysis suggests that the sequence of structural transitions of CaBe2P2O8 is associated with the electronic transformation from predominantly molecular orbitals at low pressure to the state with overlapping electronic clouds of anions orbitals.

High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re2(N2)(N)2 stable at ambient conditions.

High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K0 = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re2(N2)(N)2. Unlike known transition metals pernitrides Re2(N2)(N)2 contains both pernitride N24- and discrete N3- anions, which explains its exceptional properties. Re2(N2)(N)2 can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambient conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH4N3, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re2(N2)(N)2 turned to be at a threshold for superhard materials.