scholarly journals Unconventional Stoichiometries of Na–O Compounds at High Pressures

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7650
Author(s):  
Lihua Yang ◽  
Yukai Zhang ◽  
Yanli Chen ◽  
Xin Zhong ◽  
Dandan Wang ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Stability Field ◽  
First Principles Calculations ◽  
One Dimensional ◽  
Theoretical Investigations ◽  
Systematic Structure ◽  
Pressure Stability ◽  
The Stability ◽  
New Compounds

It has been realized that the stoichiometries of compounds may change under high pressure, which is crucial in the discovery of novel materials. This work uses systematic structure exploration and first-principles calculations to consider the stability of different stoichiometries of Na–O compounds with respect to pressure and, thus, construct a high-pressure stability field and convex hull diagram. Four previously unknown stoichiometries (NaO5, NaO4, Na4O, and Na3O) are predicted to be thermodynamically stable. Four new phases (P2/m and Cmc21 NaO2 and Immm and C2/m NaO3) of known stoichiometries are also found. The O-rich stoichiometries show the remarkable features of all the O atoms existing as quasimolecular O2 units and being metallic. Calculations of the O–O bond lengths and Bader charges are used to explore the electronic properties and chemical bonding of the O-rich compounds. The Na-rich compounds stabilized at extreme pressures (P > 200 GPa) are electrides with strong interstitial electron localization. The C2/c phase of Na3O is found to be a zero-dimensional electride with an insulating character. The Cmca phase of Na4O is a one-dimensional metallic electride. These findings of new compounds with unusual chemistry might stimulate future experimental and theoretical investigations.

Phase Stability and Elastic Properties of оne Dimensional Long Period Structures of Al3Ti under High Pressure

2016 ◽  
Vol 850 ◽  
pp. 354-361
Author(s):  
Ping Ying Tang ◽  
Guo Hua Huang ◽  
Qing Lian Xie ◽  
Jin Li Huang
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Elastic Properties ◽  
Phase Stability ◽  
Antiphase Boundary ◽  
First Principles Calculations ◽  
One Dimensional ◽  
Long Period ◽  
Phase Transition Pressure ◽  
Order Polynomial

Phase stability and elastic properties of seven one dimensional long period structures (1D-LPSs) of Al3Ti under high pressure have been systematically investigated by first-principles calculations. The enthalpy differences indicate that Al3Ti will undergo a phase transition from 1D-LPSs to L12 structure at high pressure. With increase of antiphase boundary period parameter M’, the enthalpy initially decreases and then increases, and the enthalpy for D023 is the smallest. Oppositely, the phase transition pressure firstly increases and then decreases, and the maximum is for D023. The elastic constants and elastic moduli B, G and E increase monotonically with increase of pressure, and the corresponding second-order polynomial fits are also obtained. Interestingly, the pressure dependence of Poisson’s ratio show similar tendency with that of B/G ratio. Both the B/G ratios and the Cauchy pressures reveal that these 1D-LPSs exhibit brittleness at high pressure.

scholarly journals Crystal structures and dynamical properties of dense CO2

2016 ◽  
Vol 113 (40) ◽  
pp. 11110-11115 ◽  
Author(s):  
Xue Yong ◽  
Hanyu Liu ◽  
Min Wu ◽  
Yansun Yao ◽  
John S. Tse ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Theoretical Calculations ◽  
Ambient Pressure ◽  
Md Simulations ◽  
Ab Initio Molecular Dynamics ◽  
Structural Polymorphism ◽  
Stability Structure ◽  
Dynamical Properties ◽  
The Stability

Structural polymorphism in dense carbon dioxide (CO2) has attracted significant attention in high-pressure physics and chemistry for the past two decades. Here, we have performed high-pressure experiments and first-principles theoretical calculations to investigate the stability, structure, and dynamical properties of dense CO2. We found evidence that CO2-V with the 4-coordinated extended structure can be quenched to ambient pressure below 200 K—the melting temperature of CO2-I. CO2-V is a fully coordinated structure formed from a molecular solid at high pressure and recovered at ambient pressure. Apart from confirming the metastability of CO2-V (I-42d) at ambient pressure at low temperature, results of ab initio molecular dynamics and metadynamics (MD) simulations provided insights into the transformation processes and structural relationship from the molecular to the extended phases. In addition, the simulation also predicted a phase V′(Pna21) in the stability region of CO2-V with a diffraction pattern similar to that previously assigned to the CO2-V (P212121) structure. Both CO2-V and -V′ are predicted to be recoverable and hard with a Vicker hardness of ∼20 GPa. Significantly, MD simulations found that the CO2 in phase IV exhibits large-amplitude bending motions at finite temperatures and high pressures. This finding helps to explain the discrepancy between earlier predicted static structures and experiments. MD simulations clearly indicate temperature effects are critical to understanding the high-pressure behaviors of dense CO2 structures—highlighting the significance of chemical kinetics associated with the transformations.

Phase transitions of BaCO3 at high pressures

2008 ◽  
Vol 72 (2) ◽  
pp. 659-665 ◽  
Author(s):  
S. Ono ◽  
J. P. Brodholt ◽  
G. D. Price
Keyword(s):  
Phase Transition ◽  
Experimental Study ◽  
High Pressure ◽  
Phase Transitions ◽  
Bulk Modulus ◽  
First Principles ◽  
High Pressures ◽  
Ambient Conditions ◽  
The Stability ◽  
Previous Experimental Study

AbstractFirst-principles simulations and high-pressure experiments were used to study the stability of BaCO3 carbonates at high pressures. Witherite, which is orthorhombic and isotypic with CaCO3 aragonite, is stable at ambient conditions. As pressure increases, BaCO3 transforms from witherite to an orthorhombic post-aragonite structure at 8 GPa. The calculated bulk modulus of the post-aragonite structure is 60.7 GPa, which is slightly less than that from experiments. This structure shows an axial anisotropicc ompressibility and the a axis intersects with the c axis at 70 GPa, which implies that the pressure-induced phase transition reported in previous experimental study is misidentified. Although a pyroxene-like structure is stable in Mg- and Ca-carbonates at pressures >100 GPa, our simulations showed that this structure does not appear in BaCO3.

Modifications 7 And 8 Of Decagonal AI-Co-Ni

1998 ◽  
Vol 553 ◽  
Author(s):  
S. Ritsch ◽  
K. Hiraga ◽  
C. Beeli ◽  
T. Gödecke ◽  
M. Scheffer ◽  
...  
Keyword(s):  
Rotation Axis ◽  
The Other ◽  
Stability Field ◽  
One Dimensional ◽  
Decagonal Phase ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
The Stability ◽  
Means Of Transmission ◽  
Very High

AbstractBesides the six established decagonal states of the Al-Co-Ni quasicrystal two more modifications have been discovered by means of transmission electron microscopy. One is a pentagonal quasicrystal with a superstructure found in specimens with a very high Co-content and quenched from the highest possible temperature lying within the stability field of decagonal Al-Co-Ni. Its electron diffraction patterns are characterized by a 5-fold rotation axis as a unique symmetry element as well as superstructure reflections similar to those of a related decagonal phase. The other is a one-dimensional quasicrystal closely related to decagonal Al-Co-Ni. The modulation length of 61 Å along the periodic direction in its pseudo 10-fold diffraction patterns can be assumed to be caused by a strong linear, uniform, phason strain in the material.

scholarly journals Study of silica-undersaturated magmas through the Kalsilite- Nepheline-Diopside-Silica system at 4.0 GPa and dry conditions

2018 ◽  
Vol 18 (2) ◽  
pp. 87-102
Author(s):  
Márcio Roberto Wilbert de Souza ◽  
Rommulo Vieira Conceição ◽  
Daniel Grings Cedeño ◽  
Roberto Vicente Schmitz Quinteiro
Keyword(s):  
High Pressure ◽  
Solid Solutions ◽  
Negative Correlation ◽  
Stability Field ◽  
Thermal Barrier ◽  
High Pressure And Temperature ◽  
Alkaline Magma ◽  
Magma Genesis ◽  
Dry Conditions ◽  
The Stability

This study experimentally investigates the Kalsilite-Nepheline-Diopside-Silica system at high pressure and temperature, with emphasis on silica-undersaturated volume (leucite-nepheline-diopside — Lct-Nph-Di; and kalsilite-nepheline-diopside — Kls + Nph + Di — planes), at 4.0 GPa (~120 km deep), temperatures up to 1,400ºC and dry conditions, to better understand the influence of K2O, Na2O, and CaO in alkali-rich silica-undersaturated magma genesis. In the Lct-Nph-Di plane, we determined the stability fields for kalsilite (Klsss), nepheline (Nphss) and clinopyroxene (Cpxss) solid solutions, wollastonite (Wo) and sanidine (Sa); and three piercing points: (i) pseudo-eutectic Kls + Nph + Di + liquid (Lct62Nph29Di9) at 1,000ºC; (ii) Kls + Sa + (Di + Wo) + liquid (Lct75Nph22Di2) at 1,200ºC; and (iii) pseudo-eutectic Kls + Di + Wo + liquid (Lct74Nph17Di9) at 1,000ºC. Kalsilite stability field represents a thermal barrier between ultrapotassic/potassic vs. sodic compositions. In the plane Kls-Nph-Di, we determined the stability fields for Klsss, Nphss and Cpxss and two aluminous phases in smaller proportions: spinel (Spl) and corundum (Crn). This plane has a piercing point in Kls + Nph + Di(± Spl) + liquid (Kls47Nph43Di10) at 1,100ºC. Our data showed that pressure extends K dissolution in Nph (up to 39 mol%) and Na in Kls (up to 27 mol%), and that these solid solutions, if present, determinate how much enriched in K and Na an alkaline magma will be in an alkaline-enriched metasomatic mantle. Additionally, we noted positive correlation between K2O and SiO2 concentration in experimental melts, negative correlation between CaO and SiO2, and no evident correlation between Na2O and SiO2. 

Electronic Properties of Magnetic Superconductor HoNi2B2C Under High Pressure

2003 ◽  
Vol 17 (18n20) ◽  
pp. 3664-3671 ◽  
Author(s):  
G. Oomi ◽  
N. Matsuda ◽  
T. Kagayama ◽  
C. K. Cho ◽  
P. C. Canfield
Keyword(s):  
Magnetic Field ◽  
High Pressure ◽  
Electrical Resistivity ◽  
Fermi Liquid ◽  
High Pressures ◽  
Metamagnetic Transition ◽  
Liquid Behavior ◽  
The Stability ◽  
Normal Fermi ◽  
Fermi Liquid Behavior

The electrical resistivity of single crystalline HoNi 2 B 2 C has been measured at high pressure and magnetic fields. The three anomalies in the magnetoresistance due to metamagnetic transitions are observed both at ambient and high pressures. It is found that the metamagnetic transition fields increase with increasing pressure. The temperature dependence of electrical resistivity is strongly dependent on magnetic field. Non Fermi liquid behavior is observed near the metamagnetic transition fields. But the normal Fermi liquid behavior recovers after completing the phase transition. The Grüneisen parameters are also calculated to examine the stability of electronic state.

Theoretical studies of structural stability at high pressure

1995 ◽  
Vol 73 (5-6) ◽  
pp. 253-257 ◽  
Author(s):  
John S. Tse ◽  
Dennis D. Klug
Keyword(s):  
Molecular Dynamics ◽  
High Pressure ◽  
First Principles ◽  
High Pressures ◽  
Structural Phase ◽  
Md Simulations ◽  
Quantum Molecular Dynamics ◽  
First Principles Calculations ◽  
Quantum Mechanical Effects ◽  
Structural Memory

Theoretical methods are indispensible for the study of matter at high pressure. In the last decade the development of accurate intermolecular potentials and the methodologies in classical molecular dynamics (MD) simulations have greatly facililated the applications of these methods to the study of structural phase transformamtions of solids at high pressures. More recently, it has been possible to incorporate quantum mechanical effects into MD calculations. This method eliminates a great deal of empiricism. These first principles calculations have not only reproduced the experimental results for phase transformations but also provided detailed mechanisms and in some cases predicted new structures that may be found at high pressures. The success of MD calculations is illustrated through a review of our studies of pressure-induced amorphization and phase transitions in SiO2 and TiO2, and the structural memory effect in several materials. Current applications using quantum molecular dynamics on ice are discussed.

scholarly journals New insights on the GeSe x Te1−x phase diagram from theory and experiment

2019 ◽  
Vol 75 (2) ◽  
pp. 246-256 ◽  
Author(s):  
Markus Guido Herrmann ◽  
Ralf Peter Stoffel ◽  
Michael Küpers ◽  
Mohammed Ait Haddouch ◽  
Andreas Eich ◽  
...  
Keyword(s):  
Phase Diagram ◽  
High Pressure ◽  
Low Temperature ◽  
Hexagonal Phase ◽  
Structure Type ◽  
Stability Field ◽  
Temperature Behaviour ◽  
Formation Enthalpies ◽  
The Stability

The high-pressure and low-temperature behaviour of the GeSe x Te1−x system (x = 0, 0.2, 0.5, 0.75, 1) was studied using a combination of powder diffraction measurements and first-principles calculations. Compounds in the stability field of the GeTe structure type (x = 0, 0.2, 0.5) follow the high-pressure transition pathway: GeTe-I (R3m) → GeTe-II (f.c.c.) → GeTe-III (Pnma). The newly determined GeTe-III structure is isostructural to β-GeSe, a high-pressure and high-temperature polymorph of GeSe. Pressure-dependent formation enthalpies and stability regimes of the GeSe x Te1−x polymorphs were studied by DFT calculations. Hexagonal Ge4Se3Te is stable up to at least 25 GPa. Significant differences in the high-pressure and low-temperature behaviour of the GeTe-type structures and the hexagonal phase are highlighted. The role of Ge...Ge interactions is elucidated using the crystal orbital Hamilton population method. Finally, a sketch of the high-pressure phase diagram of the system is provided.

Geochronological evidence for phased volcanic activity in Fife and Caithness necks, Scotland

1981 ◽  
Vol 72 (1) ◽  
pp. 1-7 ◽  
Author(s):  
R. M. Macintyre ◽  
R. A. Cliff ◽  
N. A. Chapman
Keyword(s):  
High Pressure ◽  
Volcanic Activity ◽  
Shallow Depth ◽  
Stability Field ◽  
Early Permian ◽  
Explosive Activity ◽  
Isotopic Studies ◽  
The Stability ◽  
Considerable Depth ◽  
Geochronological Evidence

AbstractIn an attempt to establish a chronology for volcanic neck emplacement and so elucidate petrogenesis, isotopic studies have been carried out on various cumulate inclusions, blocks and megacrysts which occur chiefly in association with tuffs infilling several Scottish vents. K-Ar ages of 13 samples of low-pressure cumulate minerals (biotite, hornblende and pyroxene) from necks in East Fife indicate crystallisation at shallow depth at 314 Ma. U-Pb analyses of zircons are concordant at 318 Ma suggesting they are also members of this suite and their formation is penecontemporaneous with the Namurian volcanic activity which is welldocumented stratigraphically. By 295 Ma crystallisation of anorthoclase megacrysts had been completed, perhaps from the fractionated residuum. An eruption from considerable depth (within the stability field of garnet precipitation) then broke through to the surface bearing high-pressure megacrysts. This penetrated and disrupted the early cumulates carrying them to the surface and producing the diverse vent assemblages. K-Ar dating of basanites suggest that the Duncansby Ness neck in Caithness was emplaced around 270 Ma in the early Permian. For two Fife necks the balance of evidence favours an age of 290 Ma (Stephanian) for this final explosive activity associated with vent formation.

scholarly journals The Effect of Pulsed Laser Heating on the Stability of Ferropericlase at High Pressures

Minerals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 542
Author(s):  
Georgios Aprilis ◽  
Anna Pakhomova ◽  
Stella Chariton ◽  
Saiana Khandarkhaeva ◽  
Caterina Melai ◽  
...  
Keyword(s):  
High Pressure ◽  
Lower Mantle ◽  
Laser Heating ◽  
High Pressures ◽  
Pulsed Laser ◽  
Experimental Conditions ◽  
Lowermost Part ◽  
The Stability ◽  
Pulsed Laser Heating ◽  
Calcium Silicate Perovskite

It is widely accepted that the lower mantle consists of mainly three major minerals—ferropericlase, bridgmanite and calcium silicate perovskite. Ferropericlase ((Mg,Fe)O) is the second most abundant of the three, comprising approximately 16–20 wt% of the lower mantle. The stability of ferropericlase at conditions of the lowermost mantle has been highly investigated, with controversial results. Amongst other reasons, the experimental conditions during laser heating (such as duration and achieved temperature) have been suggested as a possible explanation for the discrepancy. In this study, we investigate the effect of pulsed laser heating on the stability of ferropericlase, with a geochemically relevant composition of Mg0.76Fe0.24O (Fp24) at pressure conditions corresponding to the upper part of the lower mantle and at a wide temperature range. We report on the decomposition of Fp24 with the formation of a high-pressure (Mg,Fe)3O4 phase with CaTi2O4-type structure, as well as the dissociation of Fp24 into Fe-rich and Mg-rich phases induced by pulsed laser heating. Our results provide further arguments that the chemical composition of the lower mantle is more complex than initially thought, and that the compositional inhomogeneity is not only a characteristic of the lowermost part, but includes depths as shallow as below the transition zone.

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