Magnesium chloride hydrates show a rich diversity of structural forms, with different hydration numbers ranging from 1 to 12. We show that this structural versatility is also present within the same hydration numbers, with the formation of a new phase of magnesium chloride decahydrate (MgCl210H2O-II) stable at the conditions of 0.03-0.40(14) GPa at 234(11) K and up to 2.11(3) GPa at 220(2) K, as determined by in situ single-crystal X-ray diffraction. The hydrogen bonding interactions of MgCl210H2O-II are identified and the bulk modulus determined at B 0 = 18.9(12) GPa at 220(2) K. We discuss the implication of this high-pressure MgCl2 hydrate for icy moon compositional investigations and showcase the structural and density changes between the various hydrates in MgCl2nH2O.

Subsurface oceans inside icy moons are expected to contain dissolved salts whose crystallization controls the mineralogy of their hydrospheres and potentially their surfaces. Here, we use in situ neutron diffraction to investigate the isobaric crystallization of a nearly saturated MgCl2:D2O solution between ambient pressure and 0.4 GPa. At ambient pressure, substantial supercooling leads primarily to MgCl2·12D2O, whereas increasing the pressure to only 0.1 GPa fundamentally changes the crystallization pathway, yielding the recently discovered MgCl2·10D2O-II as the dominant hydrate throughout the 0.1–0.4 GPa range. The simple isobaric route enables reproducible preparation of decahydrate-II, opening the door to future studies, including spectroscopic characterization relevant to its remote detection on icy moons. We further determine a new thermal equation of state and reveal a curious contrast between its responses to pressure and temperature: the most compressible crystallographic direction exhibits the smallest thermal expansion. These findings demonstrate the importance of pressure for understanding salt-hydrate crystallization and icy-moon mineralogy.

Retraction of 'Carbon content drives high temperature superconductivity in a carbonaceous sulfur hydride below 100 GPa' by G. Alexander Smith et al., Chem. Commun., 2022, 58, 9064-9067, https://doi.org/10.1039/D2CC03170A.

Much of Earth’s carbon may have been stripped away from the silicate mantle by dense metallic-iron during core formation. However, at deep magma ocean conditions carbon becomes less siderophile and thus large amounts of it may be stranded instead in the deep mantle. Here, we describe the structure and compaction mechanisms of carbonate glass to deep mantle pressures. Our results, based on non-resonant inelastic X-ray scattering, X-ray diffraction and ab initio calculations, demonstrate a pressure-induced change in hybridization of carbon from sp 2 to sp 3 starting at 40 GPa, due to the conversion of [3] CO 3 2- groups into [4] CO 4 4- units, which is completed at ~112 GPa. The pressure-induced change of carbon coordination number from three to four increases possibilities for carbon-oxygen interactions with lower mantle silicate melts. sp 3 hybridized carbon provides a mechanism for changing the presumed siderophile nature of deep carbon, becoming a possible source for carbon-rich emissions registered at the surface in intra-plate and near-ridge hot spots.

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·17H 2 O (SC8.5); NaCl·13H 2 O (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 H 2 O–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.

The high-pressure behavior of jamesonite (FePb4Sb6S14, a = 4.08(3) Å, b = 19.08(3) Å, c = 15.67(3) Å, β= 91.89°, space group P21/c) has been investigated using in situ HP synchrotron X-ray single-crystal diffraction up to ~17 GPa with a diamond anvil cell under hydrostatic conditions. Results of the volume isothermal equation of state (EoS), determined by fitting the P-V data with a third-order Birch–Murnaghan (BM) EoS, are V0 = 1207.1(4) Å3, K0 = 36(1) GPa and K’ = 5.7(7). At high pressure, jamesonite undergoes a phase transition to an orthorhombic structure with a Pmcb space group (β-jamesonite). The analysis of β-jamesonite’s compressibility up to 16.6 GPa, studied by fitting the data with a second-order BM-EoS, gives V0 = 1027(2) Å3, K0 = 74(2) GPa. The comparison of the structural refinements at different pressures indicates that Fe, Pb and Sb do not change their coordination number over the whole investigated P range, respectively, 6 for Fe, 7 and 8 for Pb and 5 + 2 for Sb. However, a significant change occurs on the orientation of Sb lone electron pairs upon the phase transition in accordance with the change in symmetry. Furthermore, a discontinuity in the Fe chain evolution at the transition pressure is observed.

Thin film layer-by-layer room-temperature synthesis of targeted DUT-8 MOFs from 2,6-ndc and dabco ligands give different crystalline framework growths depending on the metal cation used: Cu(2,6-ndc) and Zn(2,6-ndc)(H2O).

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.

We report a previously unobserved superconducting state of the photosynthesized carbonaceous sulfur hydride (C-S-H) system with a maximum T-C of 191(1) K below 100 GPa. The properties of C-S-H are dependent on carbon content, and X-ray diffraction and simulations reveal the system remains molecular-like up to 100 GPa.

In this paper, high-pressure data from a synchrotron X-ray diffraction study on a lillianite (Pb3Bi2S6) single crystal up to similar to 21 GPa are presented. A phase transition from lillianite (space group Bbmm, LP lillianite) to the high-pressure form beta-Pb3Bi2S6 (space group Pbnm, HP lillianite) was confirmed and bracketed between 4.90 and 4.92 GPa. The transition is reversible but of first-order with a hysteresis of similar to 2.8 GPa. It showed weak effects of pseudo-merohedral twinning that disappeared upon decompression, testifying to a full recovery of the single crystal of lillianite This makes lillianite an interesting shape-memory material. With a bulk modulus K-4.9 = 78(3) GPa and K' = 5.1(4), beta-Pb3Bi2S6 is markedly less compressible than lillianite [K-0 = 44(2) GPa, K' = 7(1)]. Compressional anisotropy increases markedly in beta-Pb3Bi2S6 with compressibility along the b axis [M-0b = 130(6) GPa and M-b' = 19(3) in lillianite, M-4.9b = 145(4) GPa and M-b' = 16.0(7) in beta-Pb3Bi2S6] significantly larger than that along the other two axes [M-0a = 118(5) GPa, M-a' = 21(3), M-0c = 139(12) GPa, and M-c' = 31(10) in lillianite, M-4.9a = 242(12) GPa, M-a' = 8(1), M-4.9c = 242(5) GPa, and M-c' = 29(1) in beta-Pb3Bi2S6]. The behavior of lillianite at high pressure is an interesting case study in relation to non-quenchable ultrahigh-pressure phases likely occurring in the inner Earth, like post-perovskite MgSiO3, the oxide homologue N = 1 of the lillianite series. The beta-Pb3Bi2S6 structure, on the other hand, is the N = 3 homologue of the meneghinite series to which the higher-pressure modification of the post-perovskite structure also belongs (homologue N = 1). This makes the two forms of Pb3Bi2S6 potential equivalents of high- and ultrahigh-pressure Mg silicates that could occur both in the deep earth and in other rocky extrasolar planetary bodies.

The high-pressure phase-transition behaviour of metal-organic frameworks and coordination polymers upon varying degrees of X-ray irradiation are highlighted with four example studies. These show that, in certain cases, the radiation damage, while not extreme in changing unit-cell values, can impact the existence of a phase transition. In particular, pressure-induced phase transitions are suppressed after a certain absorbed dose threshold is reached for the sample. This is thought to be due to partial amorphization and/or defect formation in the sample, hindering the co-operative structural distortions needed for a phase transition. The high-pressure experiments were conducted with several crystals within the sample chamber in order to measure crystals with minimal X-ray irradiation at the highest pressures, which are compared with the crystals measured continuously upon pressure increase. Ways to minimize radiation damage are also discussed within the frame of high-pressure experiments.

This paper investigates the effect of KOH and NaOH on C-S-H structure and solubility. Both KOH and NaOH have a similar effect, they increase pH values and silicon concentrations, and decrease calcium concentrations. At higher alkali hydroxide concentrations, more portlandite precipitates, while amorphous silica dissolves. This increases the Ca/SiC-S-H at low Ca/Si-target but lowers the maximum Ca/Si(C-S-H )from 1.5 to 1.2 in 1 M KOH/NaOH. The amount of alkalis bound in C-S-H increases with increasing alkali hydroxide concentrations and is higher at low Ca/SiC-S-H. KOH/NaOH lead to a structural rearrangement in C-S-H, increasing the interlayer distance, number of layers stacked in c direction and shortening the silica chains. The mean chain lengths (MCL) estimated from FTIR and Raman spectroscopy agree well with the trends from Si-29 NMR. Comparison with the independently developed CASH+ thermodynamic model showed a good agreement between the observed and modelled changes, including the shortening of the MCL.

Herein we report the synthesis and structures of [(CH3)2NH2]Er(HCO2)2(C2O4) and [(NH2)3C]Er(HCO2)2(C2O4), in which the inclusion of divalent oxalate ligands allows for the exclusive incorporation of A+ and B3+ cations in an ABX3 hybrid perovskite structure for the first time. We rationalise the observed thermal expansion of these materials, including negative thermal expansion, and find evidence for weak antiferromagnetic coupling in [(CH3)2NH2]Er(HCO2)2(C2O4).

Electrospinning is a versatile technique to produce nanofibrous membranes with applications in filtration, biosensing, biomedical and tissue engineering. The structural and therefore physical properties of electrospun fibers can be finely tuned by changing the electrospinning parameters. The large parameter window makes it challenging to optimize the properties of fibers for a specific application. Therefore, a fundamental understanding of the multiscale structure of fibers and its correlation with their macroscopic behaviors is required for the design and production of systems with dedicated applications. In this study, we demonstrate that the properties of poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP) electrospun fibers can be tuned by changing the rotating drum speed used as a collector during electrospinning. Indeed, with the help of multiscale characterization techniques such as scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS), we observe that increasing the rotating drum speed not only aligns the fibers but also induces polymeric chain rearrangements at the molecular scale. Such changes result in enhanced mechanical properties and an increase of the piezoelectric β-phase of the PVDF-HFP fiber membranes. We detect nanostructural deformation behaviors when the aligned fibrous membrane is uniaxially stretched along the fiber alignment direction, while an increase in the alignment of the fibers is observed for randomly aligned samples. This was analyzed by performing in situ SAXS measurements coupled with uniaxial tensile loading of the fibrous membranes along the fiber alignment direction. The present study shows that fibrous membranes can be produced with varying degrees of fiber orientation, piezoelectric β-phase content, and mechanical properties by controlling the speed of the rotating drum collector during the fiber production. Such aligned fiber membranes have potential applications for neural or musculoskeletal tissue engineering.

The small-molecule crystallographic community has recently begun to assess the radiation damage impact of high intensity beams on samples. Bogdanov et al. [Acta Cryst. (2021), B77, 365–370] investigate the radiation damage impact on molecular ferroelectric crystal glycinium phosphite.

Room-temperature superconductivity was recently discovered in carbonaceous sulfur hydride (C-S-H) close to 3 Mbar. We report significant differences in the superconducting response of C-S-H, with a maximum T_C of 191(1) K, below a 1 Mbar. Variations in intensity of the C-H Raman modes reveal carbon content can vary between crystals synthesized with the same photo-induced method. Synchrotron single crystal x-ray diffraction identifies polymorphism with increasing degrees of covalency. These unique metastable states are highly sensitive to thermodynamic pathways.

The vast compositional space of Prussian blue analogues (PBAs), formula A(x)M[M'(CN)(6)](y)center dot nH(2)O, allows for a diverse range of functionality. Yet, the interplay between composition and physical properties-e.g., flexibility and propensity for phase transitions-is still largely unknown, despite its fundamental and industrial relevance. Here we use variable-pressure X-ray and neutron diffraction to explore how key structural features, i.e., defects, hydration, and composition, influence the compressibility and phase behavior of PBAs. Defects enhance the flexibility, manifesting as a remarkably low bulk modulus (B-0 approximate to 6 GPa) for defective PBAs. Interstitial water increases B-0 and enables a pressure-induced phase transition in defective systems. Conversely, hydration does not alter the compressibility of stoichiometric MnPt(CN)(6), but changes the high-pressure phase transitions, suggesting an interplay between low-energy distortions. AMnCo(CN)(6) (A(I) = Rb, Cs) transition from F (4) over bar 3m to P (4) over bar n2 upon compression due to octahedral tilting, and the critical pressure can be tuned by the A-site cation. At 1 GPa, the symmetry of Rb0.87Mn[Co(CN)(6)](0.91) is further lowered to the polar space group Pn by an improper ferroelectric mechanism. These fundamental insights aim to facilitate the rational design of PBAs for applications within a wide range of fields.

An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

High-pressure behavior of hexamthyleneteramine(urotropine) was studied in situusing angle-dispersive single-crystal synchrotron X-ray diffraction (XRD) andFourier transform infrared absorption (FTIR) spectroscopy. Experiments were conducted in various pressure transmitting media (helium and neon for XRD, nitrogenand KBr for FTIR experiments) to study the effect of deviatoric stress on phasetransformations. Contrary to As4O6 arsenolite, a materialof similar cage-like molecular structure, no pressure-induced heliumpenetration into the crystal structure was observed. Instead, two pressure-inducedstructural changes are observed. The first one is suggested by the followingoccurrences: (i) gradual quenching of the magnitudes of atomic displacementparameters, (ii) diminishing libration contribution to the experimental C−Nbond length, (iii) discontinuity in calculated IR-active vibrational modes and(iv) asymptotically vanishing discrepancy between the experimental andDFT‑calculated unit cell volume. All these features reach a plateau at ~4 GPaand can be attributed to a damping of molecular librations and atomic thermalmotion, pointing to the existence of a second-order isostructural phasetransition. The second transformation, with an onset at ~12.5 GPais a first-order phase transition to a tetragonal structure, characterized bysluggish kinetics and considerable hysteresis upon decompression. However, itoccurs only in non-hydrostatic conditions, induced by a deviatoric stress inthe sample. This behavior finds analogies in similar cubic crystals built ofhighly symmetric cage-like molecules and maybe considered a common feature of such systems. Last but not least, it isworth noting successful Hirshfeld atom refinements, carried out for theincomplete high-pressure diffraction data up to 14 GPa, yielded more realisticC−H bond lengths than the independent atom model.