Dense Hydrated Magnesium Carbonate MgCO·3HO Phases.

The study of the structural stability of carbonates under different pressure and temperature conditions is important for modeling the carbon budget in the Earth's interior and the stability of carbonation products of carbon capture and storage (CCS) solutions. In this work, we confirm the existence of the two dense polymorphs of the hydrated magnesium carbonate MgCO·3HO nesquehonite mineral previously reported, and we characterize their structures using synchrotron single-crystal X-ray diffraction at 3.1 and 11.

Size-Dependent High-Pressure Behavior of Pure and Eu-Doped YO Nanoparticles: Insights from Experimental and Theoretical Investigations.

We report a joint high-pressure experimental and theoretical study of the structural, vibrational, and photoluminescent properties of pure and Eu-doped cubic YO nanoparticles with two very different average particle sizes. We compare the results of synchrotron X-ray diffraction, Raman scattering, and photoluminescence measurements in nanoparticles with ab initio density-functional simulations in bulk material with the aim to understand the influence of the average particle size on the properties of pure and doped YO nanoparticles under compression. We observe that the high-pressure phase behavior of YO nanoparticles depends on the average particle size, but in a different way to that previously reported.

Polymorphism and Phase Stability of Hydrated Magnesium Carbonate Nesquehonite MgCO·3HO: Negative Axial Compressibility and Thermal Expansion in a Cementitious Material.

The - phase diagram of the hydrated magnesium carbonate nesquehonite (MgCO·3HO) has not been reported in the literature. In this paper, we present a joint experimental and computational study of the phase stability and structural behavior of this cementitious material at high-pressure and high-temperature conditions using single-crystal and synchrotron powder X-ray diffraction measurements in resistive-heated diamond anvil cells plus density functional theory calculations. Our results show that nesquehonite undergoes two pressure-induced phase transitions at 2.

Structural Behavior of Minrecordite Carbonate Mineral upon Compression: Effect of Mg → Zn Chemical Substitution in Dolomite-Type Compounds.

We report the structural behavior and compressibility of minrecordite, a naturally occurring Zn-rich dolomite mineral, determined using diamond-anvil cell synchrotron X-ray diffraction. Our data show that this rhombohedral CaZnMg(CO) carbonate exhibits a highly anisotropic behavior, the axis being 3.3 times more compressible than the axis.

Pressure-Induced Phase Transition and Band Gap Decrease in Semiconducting β-CuVO.

The understanding of the interplay between crystal structure and electronic structure in semiconductor materials is of great importance due to their potential technological applications. Pressure is an ideal external control parameter to tune the crystal structures of semiconductor materials in order to investigate their emergent piezo-electrical and optical properties. Accordingly, we investigate here the high-pressure behavior of the semiconducting antiferromagnetic material β-CuVO, finding it undergoes a pressure-induced phase transition to γ-CuVO below 4000 atm.

Crystal Structure of BaCa(CO) Alstonite Carbonate and Its Phase Stability upon Compression.

New single-crystal X-ray diffraction experiments and density functional theory (DFT) calculations reveal that the crystal chemistry of the CaO-BaO-CO system is more complex than previously thought. We characterized the BaCa(CO) alstonite structure at ambient conditions, which differs from the recently reported crystal structure of this mineral in the stacking of the carbonate groups. This structural change entails the existence of different cation coordination environments.

Post-tilleyite, a dense calcium silicate-carbonate phase.

Calcium carbonate is a relevant constituent of the Earth's crust that is transferred into the deep Earth through the subduction process. Its chemical interaction with calcium-rich silicates at high temperatures give rise to the formation of mixed silicate-carbonate minerals, but the structural behavior of these phases under compression is not known. Here we report the existence of a dense polymorph of Ca(SiO)(CO) tilleyite above 8 GPa.

Dense Post-Barite-type Polymorph of PbSO Anglesite at High Pressures.

Synchrotron X-ray diffraction measurements on lead sulfate have been performed up to 67 GPa using He as pressure transmitting medium. Experiments reveal the existence of a reversible pressure-induced phase transition from the initial Pnma barite-type to the P222 post-barite-type structure at pressures above 27 GPa. This phase transition involves a volume collapse of 2.

High-Pressure High-Temperature Stability and Thermal Equation of State of Zircon-Type Erbium Vanadate.

The zircon to scheelite phase boundary of ErVO has been studied by high-pressure and high-temperature powder and single-crystal X-ray diffraction. This study has allowed us to delimit the best synthesis conditions of its scheelite-type phase, determine the ambient-temperature equation of state of the zircon and scheelite-type structures, and obtain the thermal equation of state of the zircon-type polymorph. The results obtained with powder samples indicate that zircon-type ErVO transforms to scheelite at 8.

Peptide metal-organic frameworks under pressure: flexible linkers for cooperative compression.

We investigate the structural response of a dense peptide metal-organic framework using in situ powder and single-crystal X-ray diffraction under high-pressures. Crystals of Zn(GlyTyr) show a reversible compression by 13% in volume at 4 GPa that is facilitated by the ability of the peptidic linker to act as a flexible string for a cooperative response of the structure to strain. This structural transformation is controlled by changes to the conformation of the peptide, which enables a bond rearrangement in the coordination sphere of the metal and changes to the strength and directionality of the supramolecular interactions specific to the side chain groups in the dipeptide sequence.

An Ultrahigh CO-Loaded Silicalite-1 Zeolite: Structural Stability and Physical Properties at High Pressures and Temperatures.

We report the formation of an ultrahigh CO-loaded pure-SiO silicalite-1 structure at high pressure (0.7 GPa) from the interaction of empty zeolite and fluid CO medium. The CO-filled structure was characterized in situ by means of synchrotron powder X-ray diffraction.

Structural Behavior of Natural Silicate-Carbonate Spurrite Mineral, Ca(SiO)(CO), under High-Pressure, High-Temperature Conditions.

We report on high-pressure and high-temperature angle-dispersive synchrotron X-ray diffraction and high-pressure Raman data up to 27 GPa and 700 K for natural silicate carbonate Ca(SiO)(CO) spurrite mineral. No phase transition was found in the studied P-T range. The room-temperature bulk modulus of spurrite using Ne as the pressure-transmitting medium is B = 77(1) GPa with a first-pressure derivative of B' = 5.

Pressure Impact on the Stability and Distortion of the Crystal Structure of CeScO.

The effects of high pressure on the crystal structure of orthorhombic (Pnma) perovskite-type cerium scandate were studied in situ under high pressure by means of synchrotron X-ray powder diffraction, using a diamond-anvil cell. We found that the perovskite-type crystal structure remains stable up to 40 GPa, the highest pressure reached in the experiments. The evolution of unit-cell parameters with pressure indicated an anisotropic compression.

Exploring the Chemical Reactivity between Carbon Dioxide and Three Transition Metals (Au, Pt, and Re) at High-Pressure, High-Temperature Conditions.

The role of carbon dioxide, CO, as oxidizing agent at high pressures and temperatures is evaluated by studying its chemical reactivity with three transition metals: Au, Pt, and Re. We report systematic X-ray diffraction measurements up to 48 GPa and 2400 K using synchrotron radiation and laser-heating diamond-anvil cells. No evidence of reaction was found in Au and Pt samples in this pressure-temperature range.

Polymorphism in Strontium Tungstate SrWO under Quasi-Hydrostatic Compression.

The structural and vibrational properties of SrWO have been studied experimentally up to 27 and 46 GPa, respectively, by angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy measurements as well as using ab initio calculations. The existence of four polymorphs upon quasi-hydrostatic compression is reported. The three phase transitions were found at 11.

Crystal behavior of potassium bromate under compression.

We report on high-pressure angle-dispersive X-ray diffraction data up to 15 GPa and ab initio total-energy calculations up to 242 GPa for KBrO3. No phase transition was found below 15 Pa in contrast to previously reported data. Its experimental bulk modulus in the quasi-hydrostatic regime is B0 = 18.

Experimental and Theoretical Investigations on Structural and Vibrational Properties of Melilite-Type Sr2ZnGe2O7 at High Pressure and Delineation of a High-Pressure Monoclinic Phase.

We report a combined experimental and theoretical study of melilite-type germanate, Sr2ZnGe2O7, under compression. In situ high-pressure X-ray diffraction and Raman scattering measurements up to 22 GPa were complemented with first-principles theoretical calculations of structural and lattice dynamics properties. Our experiments show that the tetragonal structure of Sr2ZnGe2O7 at ambient conditions transforms reversibly to a monoclinic phase above 12.

Compression of silver sulfide: X-ray diffraction measurements and total-energy calculations.

Angle-dispersive X-ray diffraction measurements have been performed in acanthite, Ag(2)S, up to 18 GPa in order to investigate its high-pressure structural behavior. They have been complemented by ab initio electronic structure calculations. From our experimental data, we have determined that two different high-pressure phase transitions take place at 5 and 10.

High-pressure experimental study on Rb2S: antifluorite to Ni2In-type phase transitions.

The high-pressure behaviour of dirubidium sulfide, Rb(2)S, with antifluorite-type structure under room conditions (space group Fm ̄3m) has been studied up to 8 GPa at room temperature using angle-dispersive X-ray powder diffraction in a diamond-anvil cell (DAC). X-ray measurements have allowed us to completely characterize two phase transitions upon compression: (i) to an anticotunnite-type structure (Pnma) at some pressure between 1 bar and 0.7 GPa, and (ii) to a Ni(2)In-type structure (P6(3)/mmc) at 2.

Structural characterization of a new high-pressure phase of GaAsO4.

As in SiO2 which, at high pressures, undergoes the alpha-quartz-->stishovite transition, GaAsO4 transforms into a dirutile structure at 9 GPa and 1173 K. In 2002, a new GaAsO4 polymorph was found by quenching the compound from 6 GPa and 1273 K to ambient conditions. The powder diagram was indexed on the basis of a hexagonal cell (a=8.

Anions in metallic matrices model: application to the aluminium crystal chemistry.

We introduce and discuss an interpretative model of the structure and bonding of inorganic crystals containing metallic elements. The central idea is the conception of the crystal structure of such an inorganic compound as a metallic matrix whose geometric and electronic structures govern the formation and localization of the anions in the lattice. This is the reason for labelling the model anions in metallic matrices (AMM).

The Zintl-Klemm concept applied to cations in oxides. I. The structures of ternary aluminates.

The structures of 94 ternary aluminates are reinterpreted on the basis of the Zintl-Klemm concept and Pearson's generalized octet rule. In aluminates of highly electropositive metals such as alkali, alkaline-earth and rare-earth metals, the Al atoms form three-dimensional skeleta which can be interpreted as if the Al atoms were behaving as Zintl polyanions, adopting the structure of either main-group elements or Zintl polyanions showing the same connectivity. The O atoms are then located close to both the hypothetical two-electron bonds and the lone pairs, giving rise to a tetrahedral coordination.