RESUMEN
The anhydrous alkaline earth metal carbonate Be(CO3) was synthesized in a laser-heated diamond anvil cell at moderate pressures and temperatures (20(2) GPa and 1500(200) K) by a reaction of BeO with CO2. It crystallizes in the acentric, trigonal space group P3121 with Z = 3. The crystal structure was obtained from synchrotron single crystal X-ray diffraction data and confirmed by density functional theory-based calculations in combination with Raman spectroscopy. Second harmonic generation measurements were employed to verify the acentric space group symmetry. The crystal structure of Be(CO3) is characterized by the presence of isolated [CO3]2--groups and BeO4-tetrahedra. This is a new structure type and such a topology has not been observed in carbonates before. Be(CO3) can be recovered to ambient conditions and is not undergoing a phase transition during decompression.
RESUMEN
The research for wurtzite-type ternary nitride semiconductors containing earth abundant elements with a stoichiometry of 1 : 1 : 2 was focused on metals like Mg or Zn, so far. The vast majority of these Grimm-Sommerfeld analogue compounds crystallize in the ß-NaFeO2 structure, although a second arrangement in space group Pmc21 is predicted to be a viable alternative. Despite extensive theoretical and experimental studies, this structure has so far remained undiscovered. Herein, we report on BeGeN2 in a Pmc21 structure, synthesized from Be3N2 and Ge3N4 using a high-pressure high-temperature approach at 6â GPa and 800 °C. The compound was characterized by powder X-ray diffraction (PXRD), solid state nuclear magnetic resonance (NMR), Raman and energy dispersive X-ray (EDX) spectroscopy, temperature-dependent PXRD, second harmonic generation (SHG) and UV/Vis measurements and in addition also compared to its lighter homologue BeSiN2 in all mentioned analytic techniques. The synthesis and investigation of both the first beryllium germanium nitride and the first ternary wurtzite-type nitride crystallizing in space group Pmc21 open the door to a new field of research on wurtzite-type related structures.
RESUMEN
Nitridophosphates, with their primary structural motif of isolated or condensed PN4 tetrahedra, meet many requirements for high performance materials. Their properties are associated with their structural diversity, which is mainly limited by this specific building block. Herein, we present the alkaline earth metal nitridophosphate oxide Ba3[PN3]O featuring a trigonal planar [PN3]4- anion. Ba3[PN3]O was obtained using a hot isostatic press by medium-pressure high-temperature synthesis (MP/HT) at 200â MPa and 880 °C. The crystal structure was solved and refined from single-crystal X-ray diffraction data in space group R 3 â¾ ${\bar 3}$ c (no. 167) and confirmed by SEM-EDX, magic angle spinning (MAS) NMR, vibrational spectroscopy (Raman, IR) and low-cost crystallographic calculations (LCC). MP/HT synthesis reveals great potential by extending the structural chemistry of P to include trigonal planar [PN3]4- motifs.
RESUMEN
An atomistic pathway for a strain-induced subsolidus martensitic transition between quartz and coesite was found by computing the set of the smallest atomic displacements required to transform a quartz structure into a coesite structure. A minimal transformation cell with 24 [Formula: see text] formula units is sufficient to describe the diffusionless martensitic transition from quartz to coesite. We identified two families of invariant shear planes during the martensitic transition, near the {10[Formula: see text]1} and {12[Formula: see text]2} set of planes, in agreement with the orientation of planar defect structures observed in quartz samples which experienced hypervelocity impacts. We calculated the reaction barrier using density functional theory and found that the barrier of 150 meV/atom is pressure invariant from ambient pressure up to 5 GPa, while the mean principal stress limiting the stability of strained quartz is [Formula: see text] 2 GPa. The model calculations quantitatively confirm that coesite can be formed in strained quartz at pressures significantly below the hydrostatic equilibrium transition pressure.
RESUMEN
Carbon nitrides featuring three-dimensional frameworks of CN4 tetrahedra are one of the great aspirations of materials science, expected to have a hardness greater than or comparable to diamond. After more than three decades of efforts to synthesize them, no unambiguous evidence of their existence has been delivered. Here, the high-pressure high-temperature synthesis of three carbon-nitrogen compounds, tI14-C3 N4 , hP126-C3 N4 , and tI24-CN2 , in laser-heated diamond anvil cells, is reported. Their structures are solved and refined using synchrotron single-crystal X-ray diffraction. Physical properties investigations show that these strongly covalently bonded materials, ultra-incompressible and superhard, also possess high energy density, piezoelectric, and photoluminescence properties. The novel carbon nitrides are unique among high-pressure materials, as being produced above 100 GPa they are recoverable in air at ambient conditions.
RESUMEN
The inorganic pyrocarbonate salt Na2[C2O5] crystallizes in the acentric, monoclinic space group P21 with Z = 2. It contains monovalent alkali metal cations together with isolated pyrocarbonate anions. The [C2O5]2--groups consist of two planar [CO3]2--groups which are slightly tilted with respect to each other around the bridging oxygen atom. Na2[C2O5] was synthesized in a laser-heated diamond anvil cell at 20(2) GPa by heating a mixture of Na2[CO3] + CO2 to ≈800(200) K. Its crystal structure was obtained by single crystal synchrotron X-ray diffraction and confirmed by density functional theory-based calculations in combination with Raman spectroscopy. Second harmonic generation measurements verified the acentric space group symmetry. The crystal structure is characterized by alternating layers of Na+-cations and [C2O5]2--complex anions.
RESUMEN
To date, experimental and theoretical works have been unable to uncover the ground-state configuration of the solid electrolyte cubic Li7La3Zr2O12 (c-LLZO). Computational studies rely on an initial low-energy structure as a reference point. Here, we present a methodology for identifying energetically favorable configurations of c-LLZO for a crystallographically predicted structure. We begin by eliminating structures that involve overlapping Li atoms based on nearest neighbor counts. We further reduce the configuration space by eliminating symmetry images from all remaining structures. Then, we perform a machine learning-based energetic ordering of all remaining structures. By considering the geometrical constraints that emerge from this methodology, we determine that a large portion of previously reported structures may not be feasible or stable. The method developed here could be extended to other ion conductors. We provide a database containing all of the generated structures with the aim of improving accuracy and reproducibility in future c-LLZO research.
RESUMEN
The inorganic pyrocarbonate salt Ba[C2O5] contains twisted pyrocarbonate anions ([C2O5]2-), an atomic arrangement previously not observed in other pyrocarbonates. This unexpected additional structural degree of freedom points towards an enlarged chemical variability in this novel group of compounds. Ba[C2O5] was synthesized in a laser-heated diamond anvil cell at 30(2) GPa by heating a mixture of Ba[CO3] + CO2 to ≈ 1500(200) K. Its crystal structure was solved from single crystal synchrotron X-ray diffraction data and confirmed by density functional theory-based calculations. The two planar [CO3]2--groups of the [C2O5]2--anion are strongly twisted around the bridging oxygen atom. Ba[C2O5] has been observed in the pressure range of 5-30 GPa, where its symmetry is P6/m with Z = 12.
RESUMEN
We synthesized the inorganic anhydrous aluminum carbonates Al2[C2O5][CO3]2 and Al2[CO3]3 by reacting Al2O3 with CO2 at high pressures and temperatures and characterized them by Raman spectroscopy. Their structures were solved by X-ray diffraction. Al2[CO3]3 forms at around 24-28 GPa, while Al2[C2O5][CO3]2 forms above 38(3) GPa. The distinguishing feature of the new Al2[C2O5][CO3]2-structure type is the presence of pyrocarbonate [C2O5]2--groups, trigonal [CO3]2âgroups, and octahedrally coordinated trivalent cations. Al2[CO3]3 has isolated [CO3]2--groups. Both Al-carbonates can be recovered under ambient conditions. Density functional theory calculations predict that CO2 will react with Fe2O3, Ti2O3, Ga2O3, In2O3, and MgSiO3 at high pressures to form compounds which are isostructural to Al2[C2O5][CO3]2. MgSi[C2O5][CO3]2 is predicted to be stable at pressures relative to abundant mantle minerals in the presence of CO2. This structure type allows the incorporation of four elements (Mg, Si, Fe, and Al) abundant in the Earth's mantle in octahedral coordination and provides an alternative phase with novel carbon speciation for carbon storage in the deep Earth.
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The lanthanum-hydrogen system has attracted significant attention following the report of superconductivity in LaH10 at near-ambient temperatures and high pressures. Phases other than LaH10 are suspected to be synthesized based on both powder X-ray diffraction and resistivity data, although they have not yet been identified. Here, we present the results of our single-crystal X-ray diffraction studies on this system, supported by density functional theory calculations, which reveal an unexpected chemical and structural diversity of lanthanum hydrides synthesized in the range of 50 to 180 GPa. Seven lanthanum hydrides were produced, LaH3, LaH~4, LaH4+δ, La4H23, LaH6+δ, LaH9+δ, and LaH10+δ, and the atomic coordinates of lanthanum in their structures determined. The regularities in rare-earth element hydrides unveiled here provide clues to guide the search for other synthesizable hydrides and candidate high-temperature superconductors. The hydrogen content variability in lanthanum hydrides and the samples' phase heterogeneity underline the challenges related to assessing potentially superconducting phases and the nature of electronic transitions in high-pressure hydrides.
RESUMEN
We have synthesized Pb[C2O5], an inorganic pyrocarbonate salt, in a laser-heated diamond anvil cell (LH-DAC) at 30 GPa by heating a Pb[CO3] + CO2 mixture to ≈2000(200) K. Inorganic pyrocarbonates contain isolated [C2O5]2- groups without functional groups attached. The [C2O5]2- groups consist of two oxygen-sharing [CO3]3- groups. Pb[C2O5] was characterized by synchrotron-based single-crystal structure refinement, Raman spectroscopy, and density functional theory calculations. Pb[C2O5] is isostructural to Sr[C2O5] and crystallizes in the monoclinic space group P21/c with Z = 4. The synthesis of Pb[C2O5] demonstrates that, just like in other carbonates, cation substitution is possible and that therefore inorganic pyrocarbonates are a novel family of carbonates, in addition to the established sp2 and sp3 carbonates.
RESUMEN
We report the first direct measurements of the refractive index of silica glass up to 145 GPa that allowed quantifying its density, bulk modulus, Lorenz-Lorentz polarizability, and band gap. These properties show two major anomalies at â¼10 and â¼40 GPa. The anomaly at â¼10 GPa signals the onset of the increase in Si coordination, and the anomaly at â¼40 GPa corresponds to a nearly complete vanishing of fourfold Si. More generally, we show that the compressibility and density of noncrystalline solids can be accurately measured in simple optical experiments up to at least 110 GPa.
RESUMEN
The synthesis of a novel type of carbonate, namely of the inorganic pyrocarbonate salt Sr[C2O5], which contains isolated [C2O5]2--groups, significantly extends the crystal chemistry of inorganic carbonates beyond the established sp2- and sp3-carbonates. We synthesized Sr[C2O5] in a laser-heated diamond anvil cell by reacting Sr[CO3] with CO2. By single crystal synchrotron diffraction, Raman spectroscopy, and density functional theory (DFT) calculations, we show that it is a pyrocarbonate salt. Sr[C2O5] is the first member of a novel family of inorganic carbonates. We predict, based on DFT calculations, that further inorganic pyrocarbonates can be obtained and that these will be relevant to geoscience and may provide a better understanding of reactions converting CO2 into useful inorganic compounds.
RESUMEN
The high-pressure behavior of simple molecular systems, devoid of strong intermolecular interactions, provides a unique avenue toward a fundamental understanding of matter. Tetrahalides of the carbon group elements (group 14), lacking all intermolecular interactions but van der Waals, are among the most elementary of molecular compounds. Here, we report the investigation of CF4 up to 46.5 GPa-the highest pressure up to which any tetrahalides of group 14 elements have been studied so far-by a combination of single-crystal x-ray diffraction (SC-XRDp), Raman spectroscopy, and ab initio calculations. These measurements reveal a pressure-induced reentrant phase transition (phase II â2.8GPa phase III ââ¼20GPa phase IIR) at room temperature and the formation of a previously unknown CF4 cubic polymorph, named phase IV, after the laser heating of CF4 at 46.5 GPa. In this work, the structures of phases IIR, III, and IV were solved and the atomic coordinates were refined on the basis of SC-XRDp. A comparison of tetrahalides of group 14 elements underlines that reducing the intermolecular halogen-halogen distances leads to a structural rearrangement from close packing of the tetrahedral molecules to close packing of the halogen atoms.
RESUMEN
GaSeCl5O is a new inorganic molecular compound prepared from SeO2, SeCl4, and GaCl3 at 50 °C in quantitative yield. The structure of the title compound is described by GaCl3(OSeCl2) molecules with a tetrahedrally coordinated Ga atom and a pseudo-tetrahedrally coordinated Se atom (including lone pair of Se(IV)) that are bridged by oxygen. GaSeCl5O crystallizes in the polar chiral space group P61, which is rarely observed for molecular structures. The compound is characterized by X-ray structure analysis based on single crystals and powder samples, thermogravimetry, infrared and Raman spectroscopy as well as by second harmonic generation (SHG) measurements. The experimental data are complemented by density functional theory calculations. GaSeCl5O shows one of the strongest SHG signals known in the visible part of the electromagnetic spectrum (480-700 nm) with an SHG intensity 10 times higher than potassium dihydrogen phosphate (KDP). This is in accordance with the phase matchability and a strong dipole moment (|µ| = 8.3 D for a molecule in the crystal lattice). Such a strong SHG effect is also remarkable since GaSeCl5O-unlike most of the materials with strong SHG intensity-is an inorganic molecular compound.
RESUMEN
We have synthesized the orthocarbonate Sr3[CO4]O in a laser-heated diamond anvil cell at 20 and 30 GPa by heating to ≈3000 (300) K. Afterward, we recovered the orthocarbonate with [CO4]4- groups at ambient conditions. Single-crystal diffraction shows the presence of [CO4]4- groups, i.e., sp3-hybridized carbon tetrahedrally coordinated by covalently bound oxygen atoms. The [CO4]4- tetrahedra are located in a cage formed by corner-sharing OSr6 octahedra, i.e., octahedra with oxygen as a central ion, forming an antiperovskite-type structure. At high pressures, the octahedra are nearly ideal and slightly rotated. The high-pressure phase is tetragonal (I4/mcm). Upon pressure release, there is a phase transition with a symmetry lowering to an orthorhombic phase (Pnma), where the octahedra tilt and deform slightly.
RESUMEN
The complete elastic stiffness tensor of thiourea has been determined from thermal diffuse scattering (TDS) using high-energy photons (100â keV). Comparison with earlier data confirms a very good agreement of the tensor coefficients. In contrast with established methods to obtain elastic stiffness coefficients (e.g. Brillouin spectroscopy, inelastic X-ray or neutron scattering, ultrasound spectroscopy), their determination from TDS is faster, does not require large samples or intricate sample preparation, and is applicable to opaque crystals. Using high-energy photons extends the applicability of the TDS-based approach to organic compounds which would suffer from radiation damage at lower photon energies.
RESUMEN
We have synthesized the orthocarbonate Sr2CO4, in which carbon is tetrahedrally coordinated by four oxygen atoms, at moderately high pressures [20(1) GPa] and high temperatures (≈3500 K) in a diamond anvil cell by reacting a SrCO3 single crystal with SrO powder. We show by synchrotron powder X-ray diffraction, Raman spectroscopy, and density functional thoery calculations that this phase, and hence sp3-hybridized carbon in a CO44- group, can be recovered at ambient conditions. The C-O bond distances are all of similar lengths [≈1.41(1) Å], and the O-C-O angles deviate from the ideal tetrahedral angle by a few degrees only.
RESUMEN
At high pressures, autoionization - along with polymerization and metallization - is one of the responses of simple molecular systems to a rise in electron density. Nitro-sonium nitrate (NO+NO3 -), known for this property, has attracted a large interest in recent decades and was reported to be synthesized at high pressure and high temperature from a variety of nitro-gen-oxygen precursors, such as N2O4, N2O and N2-O2 mixtures. However, its structure has not been determined unambiguously. Here, we present the first structure solution and refinement for nitro-sonium nitrate on the basis of single-crystal X-ray diffraction at 7.0 and 37.0â GPa. The structure model (P21/m space group) contains the triple-bonded NO+ cation and the NO3 - sp 2-trigonal planar anion. Remarkably, crystal-chemical considerations and accompanying density-functional-theory calculations show that the oxygen atom of the NO+ unit is positively charged - a rare occurrence when in the presence of a less-electronegative element.
RESUMEN
High-pressure single-crystal to 20â GPa and powder diffraction measurements to 50â GPa, show that the structure of Pb2SnO4 strongly distorts on compression with an elongation of one axis. A structural phase transition occurs between 10â GPa and 12â GPa, with a change of space group from Pbam to Pnam. The resistivity decreases by more than six orders of magnitude when pressure is increased from ambient conditions to 50â GPa. This insulator-to-semiconductor transition is accompanied by a reversible appearance change from transparent to opaque. Density functional theory-based calculations show that at ambient conditions the channels in the structure host the stereochemically-active Pb 6s2 lone electron pairs. On compression the lone electron pairs form bonds between Pb2+ ions. Also provided is an assignment of irreducible representations to the experimentally observed Raman bands.