High-Pressure Properties of Na3ClO Anti-perovskite from First Principles: an exploratory study

1997 ◽  
Vol 499 ◽  
Author(s):  
A. V. G. Chizmeshya ◽  
O. F. Sankey ◽  
P. F. McMillan
Keyword(s):  
First Principles ◽  
Theoretical Study ◽  
Ambient Pressure ◽  
Lattice Energy ◽  
Cubic Phase ◽  
Compression Behavior ◽  
Symmetry Structure ◽  
Flapw Method ◽  
Static Lattice ◽  
The Ideal

ABSTRACTWe present the results of an exploratory theoretical study of Na3ClO in the anti-perovskite structure. The FLAPW method is used to calculate the static lattice properties, pressure equation of state, and the ferroic Flu phonon frequencies in the cubic PmSm phase. We also compute the compression behavior of NaCl and Na2O and find that the lattice energy of Na3ClO at ambient pressure (static lattice) is only marginally larger than of products, in agreement with experiment. However, detailed calculations reveal M- and R-point phonon instabilities in the ideal cubic phase and suggest the existence of lower symmetry structure involving slight rotations of ONa6 octahedra.

scholarly journals Hydride-based antiperovskites with soft anionic sublattices as fast alkali ionic conductors

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shenghan Gao ◽  
Thibault Broux ◽  
Susumu Fujii ◽  
Cédric Tassel ◽  
Kentaro Yamamoto ◽  
...  
Keyword(s):  
Experimental Studies ◽  
Ionic Conductivities ◽  
Cubic Phase ◽  
Ionic Conductors ◽  
Large Size ◽  
Migration Barriers ◽  
Soft Phonon Mode ◽  
Aliovalent Substitution ◽  
Cubic Forms ◽  
The Ideal

AbstractMost solid-state materials are composed of p-block anions, only in recent years the introduction of hydride anions (1s2) in oxides (e.g., SrVO2H, BaTi(O,H)3) has allowed the discovery of various interesting properties. Here we exploit the large polarizability of hydride anions (H–) together with chalcogenide (Ch2–) anions to construct a family of antiperovskites with soft anionic sublattices. The M3HCh antiperovskites (M = Li, Na) adopt the ideal cubic structure except orthorhombic Na3HS, despite the large variation in sizes of M and Ch. This unconventional robustness of cubic phase mainly originates from the large size-flexibility of the H– anion. Theoretical and experimental studies reveal low migration barriers for Li+/Na+ transport and high ionic conductivity, possibly promoted by a soft phonon mode associated with the rotational motion of HM6 octahedra in their cubic forms. Aliovalent substitution to create vacancies has further enhanced ionic conductivities of this series of antiperovskites, resulting in Na2.9H(Se0.9I0.1) achieving a high conductivity of ~1 × 10–4 S/cm (100 °C).

Fundamental Studies of Plutonium Aging

MRS Bulletin ◽  
2001 ◽  
Vol 26 (9) ◽  
pp. 679-683 ◽  
Author(s):  
Brian D. Wirth ◽  
Adam J. Schwartz ◽  
Michael J. Fluss ◽  
Maria J. Caturla ◽  
Mark A. Wall ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Conduction Band ◽  
Ambient Pressure ◽  
Radioactive Decay ◽  
Bound State ◽  
Environmental Safety ◽  
Structure Theory ◽  
Cubic Phase ◽  
High Symmetry ◽  
Safety And Health

Plutonium metallurgy lies at the heart of science-based stockpile stewardship. One aspect is concerned with developing predictive capabilities to describe the properties of stockpile materials, including an assessment of microstructural changes with age. Yet, the complex behavior of plutonium, which results from the competition of its 5f electrons between a localized (atomic-like or bound) state and an itinerant (delocalized bonding) state, has been challenging materials scientists and physicists for the better part of five decades. Although far from quantitatively absolute, electronic-structure theory provides a description of plutonium that helps explain the unusual properties of plutonium, as recently reviewed by Hecker. (See also the article by Hecker in this issue.) The electronic structure of plutonium includes five 5f electrons with a very narrow energy width of the 5f conduction band, which results in a delicate balance between itinerant electrons (in the conduction band) or localized electrons and multiple lowenergy electronic configurations with nearly equivalent energies. These complex electronic characteristics give rise to unique macroscopic properties of plutonium that include six allotropes (at ambient pressure) with very close free energies but large (∼25%) density differences, a lowsymmetry monoclinic ground state rather than a high-symmetry close-packed cubic phase, compression upon melting (like water), low melting temperature, anomalous temperature-dependence of electrical resistance, and radioactive decay. Additionally, plutonium readily oxidizes and is toxic; therefore, the handling and fundamental research of this element is very challenging due to environmental, safety, and health concerns.

On the Possibility of Passivation of Si(100) by Adsorption of Group-VI Atoms

1990 ◽  
Vol 193 ◽  
Author(s):  
Efthimios Kaxiras
Keyword(s):  
First Principles ◽  
Relative Strength ◽  
Energy Costs ◽  
First Principles Calculations ◽  
Qualitative Information ◽  
Group Vi ◽  
Covalent Bonds ◽  
Large Dispersion ◽  
Monolayer Coverage ◽  
The Ideal

ABSTRACTThe possibility of passivating the Si(100) surface by adsorption of Group-VI atoms (S and Se) is investigated through first-principles calculations. The structure of the ideal (1×1) configuration with the Si surface dangling bonds saturated by full monolayer coverage is examined in detail. The Group-VI adsorbates form covalent bonds to the substrate with bond-lengths very close to the sums of the covalent radii. The bond-angles are larger than in bulk configurations of the Group-VI elements. The ideal (1×1) configuration gives rise to a surface electronic state with large dispersion spanning the entire band-gap of Si. Deviations from this configuration by in-phase or out-of-phase tilting of the adsorbate atoms result in energy costs which can give qualitative information on the relative strength of adsorbate-adsorbate and adsorbate-substrate interactions.

Turbojet Thrust Augmentation through a Variable Exhaust Nozzle with Active Disturbance Rejection Control

Aerospace ◽  
2021 ◽  
Vol 8 (10) ◽  
pp. 293
Author(s):  
Francisco Villarreal-Valderrama ◽  
Patricia Zambrano-Robledo ◽  
Diana Hernandez-Alcantara ◽  
Luis Amezquita-Brooks
Keyword(s):  
First Principles ◽  
Disturbance Rejection ◽  
Design Method ◽  
Ambient Pressure ◽  
Stream Velocity ◽  
Exhaust Gas ◽  
Active Disturbance Rejection Control ◽  
Active Disturbance Rejection ◽  
Disturbance Rejection Control ◽  
Gain Margin

Turbojets require variable exhaust nozzles to fit high-demanding applications; however, few reports on nozzle control are available. The purpose of this paper is to investigate the possible advantages of an exhaust gas control through a variable exhaust nozzle. The control design method combines successful linear active disturbance rejection control (LADRC) capabilities with a loop shaping controller (LSC) to: (i) allow designing the closed-loop characteristics in terms of gain margin, phase margin and bandwidth, and (ii) increase the LSC disturbance rejection capabilities with an extended state observer. A representation of the nozzle dynamics is obtained from first principles and adapted to achieve a stream-velocity-based control loop. The results show that the resulting controller allows improving the expansion of the exhaust gas to the ambient pressure for the whole operating range of the turbojet, increasing the estimated thrust by 14.23% during the tests with experimental data.

scholarly journals Strain Conditions for the Inverse Heusler Type Fully Compensated Spin-Gapless Semiconductor Ti2MnAl: A First-Principles Study

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2091 ◽  
Author(s):  
Tie Yang ◽  
Liyu Hao ◽  
Rabah Khenata ◽  
Xiaotian Wang
Keyword(s):  
Thermodynamic Properties ◽  
First Principles ◽  
Density Functional ◽  
Theoretical Study ◽  
Debye Model ◽  
Pressure Effects ◽  
First Principles Calculation ◽  
Strain Condition ◽  
Functional Theory ◽  
Future Work

In this work, we systematically studied the structural, electronic, magnetic, mechanical and thermodynamic properties of the fully compensated spin-gapless inverse Heusler Ti2MnAl compound under pressure strain condition by applying the first-principles calculation based on density functional theory and the quasi-harmonic Debye model. The obtained structural, electronic and magnetic behaviors without pressure are well consistent with previous studies. It is found that the spin-gapless characteristic is destroyed at 20 GPa and then restored with further increase in pressure. While, the fully compensated ferromagnetism shows a better resistance against the pressure up to 30 GPa and then becomes to non-magnetism at higher pressure. Tetragonal distortion has also been investigated and it is found the spin-gapless property is only destroyed when c/a is less than 1 at 95% volume. Three independent elastic constants and various moduli have been calculated and they all show increasing tendency with pressure increase. Additionally, the pressure effects on the thermodynamic properties under different temperature have been studied, including the normalized volume, thermal expansion coefficient, heat capacity at constant volume, Grüneisen constant and Debye temperature. Overall, this theoretical study presents a detailed analysis of the physical properties’ variation under strain condition from different aspects on Ti2MnAl and, thus, can provide a helpful reference for the future work and even inspire some new studies and lead to some insight on the application of this material.

First Principles Theoretical Study of 4H-SiC/SiO2Interfacial Electronic States on (0001), (000\bar1), and (11\bar20)

2008 ◽  
Vol 1 ◽  
pp. 061401 ◽  
Author(s):  
Eiichi Okuno ◽  
Toshio Sakakibara ◽  
Shoichi Onda ◽  
Makoto Itoh ◽  
Tsuyoshi Uda
Keyword(s):  
First Principles ◽  
Theoretical Study ◽  
Electronic States

FIRST PRINCIPLES DENSITY FUNCTIONAL INVESTIGATION OF SUPPORTED TUNGSTEN CLUSTER (Wn; n = 1 TO 6) ON ANCHORED GRAPHITE (0001) SURFACE

2013 ◽  
Vol 02 (03n04) ◽  
pp. 1350015
Author(s):  
SONALI BARMAN ◽  
G. P. DAS ◽  
Y. KAWAZOE
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Metal Clusters ◽  
Theoretical Study ◽  
First Principles Calculations ◽  
Novel Technique ◽  
Defect Site ◽  
Positive Ions ◽  
Spin Polarized ◽  
Functional Investigation

Size-selected Wn clusters can be deposited firmly on a graphite (0001) surface using a novel technique, where the positive ions (of the same metal atom species) embedded on the graphite surface by ion implantation, act as anchors. The size selected metal clusters can then soft land on this anchored surface m [Hayakawa et al., 2009]. We have carried out a systematic theoretical study of the adsorption of Wn (n = 1-6) clusters on anchored graphite (0001) surface, using state-of-art spin-polarized density functional approach. In our first-principles calculations, the graphite (0001) surface has been suitably modeled as a slab separated by large vacuum layers. Wn clusters bond on clean graphite (0001) surface with a rather weak Van-der-Waals interaction. However, on the anchored graphite (0001) surface, the Wn clusters get absorbed at the defect site with a much larger adsorption energy. We report here the results of our first-principles investigation of this supported Wn cluster system, along with their reactivity trend as a function of the cluster size (n).

First-Principles Investigation on Elastic Constants of TiN under High Pressure

2013 ◽  
Vol 802 ◽  
pp. 109-113
Author(s):  
Kittiya Prasert ◽  
Pitiporn Thanomngam ◽  
Kanoknan Sarasamak
Keyword(s):  
Elastic Constants ◽  
First Principles ◽  
Local Density ◽  
Ambient Pressure ◽  
Lattice Parameter ◽  
First Principles Calculations ◽  
Generalized Gradient ◽  
Generalized Gradient Approximation ◽  
Shear Distortion ◽  
Calculated Lattice Parameter

Elastic constants of NaCl-type TiN under pressure were investigated by first-principles calculations within both local density approximation (LDA) and Perdew-Burke-Ernzerhof generalized-gradient approximation (PBE-GGA). At ambient pressure, the calculated lattice parameter, bulk modulus, and elastic constants of NaCl-type TiN are in well agreement with other available values. Under pressure, all elastic constants,C11,C12, andC44, are found to increase with pressure.C11, which is related to the longitudinal distortion, increases rapidly with pressure whileC12andC44which are related to the transverse and shear distortion, respectively, are much less sensitive to pressure.

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