Structural vacancy revisited: are user demands changing?

2012 ◽  
Keyword(s):  
Structural Vacancy

Pair Sites on Al3O Nodes of the Metal-Organic Framework MIL-100: Cooperative Roles of Defect and Structural Vacancy Sites in Methanol Dehydration Catalysis

2021 ◽  
Author(s):  
Shangpu Zhuang ◽  
Haodong Huang ◽  
Yue Xiao ◽  
Zhuxiu Zhang ◽  
Jihai Tang ◽  
...  
Keyword(s):  
Metal Organic Framework ◽  
Structural Vacancy ◽  
Methanol Dehydration ◽  
Metal Organic ◽  
Organic Framework

Aluminum-Based Quasicrystals Studied by Slow Positron Beam Technique

2000 ◽  
Vol 643 ◽  
Author(s):  
K. Sato ◽  
H. Uchiyama ◽  
I. Kanazawa ◽  
R. Tamura ◽  
K. Kimura ◽  
...  
Keyword(s):  
Positron Beam ◽  
Structural Vacancy ◽  
Slow Positron ◽  
S Parameter ◽  
Three Samples ◽  
Icosahedral Quasicrystals ◽  
Beam Technique

AbstractIcosahedral quasicrystals Al71.5Pd20.3Mn8.2, Al70.7Pd21.34Re7.96, Al62.5Cu25.5Fe12.5, and α-Al68.31Mn21.21Si10.48 1/1- approximant were investigated by using a monoenergetic slow positron beam. The structural vacancy densities in the first three samples were determined to be 5.0×1020, 7.7×1020, and 4.7×1020 cm−3, respectively, by analyzing the measured S-parameter.

Effect of Hydrogen on The Electronic Structure of a Grain Boundary In Iron

1990 ◽  
Vol 209 ◽  
Author(s):  
Genrich L. Krasko ◽  
Ralph J. Harrison ◽  
G. B. Olson
Keyword(s):  
Grain Boundary ◽  
Magnetic Moments ◽  
Covalent Bond ◽  
Magnetic Contribution ◽  
Structural Vacancy ◽  
Embedded Atom Method ◽  
Embedded Atom ◽  
Modified Embedded Atom Method ◽  
Almost All ◽  
Supercell Model

ABSTRACTLMTO-ASA calculations were performed on a 26-atom supercell model of a Σ3(111) grain boundary (GB) in bcc Fe. The supercell emulated two GB's with 11 (111)planes of Fe atoms between the GB planes. One of the GB's was clean, with a structural vacancy at the GB core in the center of a trigonal prism of Fe atoms, while on the other GB this site was occupied by a H atom. The interplanar spacings of the supercell were relaxed using a modified embedded atom method. As in the case of P and S in a similar GB environment in Fe there is only a weak interaction between H and nearest Fe atoms. Almost all the Fe d-states are nonbonding. A very weak covalent bond exists between H and Fe due to s-d hybridization, the hybrid bonding part located far below the Fermi energy. This bond is mostly of σ-type, connecting H with the Fe atoms in the GB plane; the δ-component of this bond across the GB is weaker. A weak electrostatic interaction attracts Fe-atoms across the clean GB, but results in repulsion if a H atom is present. The magnetic contribution to intergranular cohesion is decreased when H is present due the suppression of the magnetic moments of the nearest Fe atoms both in the GB plane and directly across the GB.

scholarly journals Structures of Impurity Defects in Lithium Niobate and Tantalate Derived from Electron Paramagnetic and Electron Nuclear Double Resonance Data

Crystals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 339
Author(s):  
Valentin G. Grachev ◽  
Galina I. Malovichko
Keyword(s):  
Lithium Niobate ◽  
Double Resonance ◽  
Charge Compensation ◽  
Dipole Approximation ◽  
Structural Vacancy ◽  
Electron Nuclear Double Resonance ◽  
Paramagnetic Resonance ◽  
Paramagnetic Impurities ◽  
Impurity Defect ◽  
Electron Paramagnetic

Point intrinsic and extrinsic defects, especially paramagnetic ions of transition metals and rare-earth elements, have essential influence on properties of lithium niobate, LN and tantalate, LT, and often determine their suitability for numerous applications. Discussions about structures of the defects in LN/LT have lasted for decades. Many experimental methods facilitate progress in determining the structures of impurity centers. This paper gives current bird’s eye view on contributions of Electron Paramagnetic Resonance (EPR), and Electron Nuclear Double Resonance (ENDOR) studies to the determination of impurity defect structures in LN and LT crystals for a broad audience of researchers and students. Symmetry and charge compensation considerations restrict a number of possible structures. Comparison of measured angular dependences of ENDOR frequencies with calculated ones for Li and Nb substitution using dipole–dipole approximation allows unambiguously to determine the exact location of paramagnetic impurities. Models with two lithium vacancies explain angular dependencies of EPR spectra for Me3+ ions substituting for Li+ like Cr, Er, Fe, Gd, Nd, and Yb. Self-compensation of excessive charges through equalization of concentrations of Me3+(Li+) and Me3+(Nb5+) and appearance of interstitial Li+ in the structural vacancy near Me3+(Nb5+) take place in stoichiometric LN/LT due to lack of intrinsic defects.

Coexisting transport behaviors in quasibinary Cd (3−3m) Ga 2m Te 3 ( m = 0.75–0.98) system with structural vacancy and cationic interdiffusion

2016 ◽  
Vol 113 ◽  
pp. 194-197
Author(s):  
Haiyun Liu ◽  
Dingqi Tian ◽  
Zhengliang Du ◽  
Jiaolin Cui
Keyword(s):  
Structural Vacancy

scholarly journals First-Principles Interatomic Potentials for Transition Metals and Their Surfaces

1990 ◽  
Vol 193 ◽  
Author(s):  
John A. Moriarty ◽  
Robert B. Phillips
Keyword(s):  
Transition Metals ◽  
First Principles ◽  
Surface Relaxation ◽  
Structural Vacancy ◽  
Interatomic Potentials ◽  
Pseudopotential Theory ◽  
Embedded Atom ◽  
Bulk Volume ◽  
Average Electron ◽  
Embedding Function

ABSTRACTFor bulk transition metals, a first-principles generalized pseudopotential theory (GPT) of interatomic potentials has been developed in which the cohesive-energy unctional takes the form of a volume term plus sums over widely transferable two-, three-, and four-ion potentials. The GPT has been further extended to surfaces by making an internal transformation of this functional to an embedded-atom-like format in which the embedding function is identified as the bulk volume term and the atomic volume is replaced by an average electron density. Applications of the bulk and surface GPT to the calculation of structural, vacancy-formation, and surface energies in Cu and Mo, and to the investigation of surface relaxation and reconstruction in Mo are discussed.

scholarly journals Базовые элементы структуры границ зерен наклона. Часть 2. Оси разориентации [110] и [111]-=SUP=-*-=/SUP=-

2021 ◽  
Vol 63 (1) ◽  
pp. 55
Author(s):  
А.В. Векман ◽  
Б.Ф. Демьянов
Keyword(s):  
Grain Boundaries ◽  
Atomic Structure ◽  
Pair Potential ◽  
Structural Vacancy ◽  
Many Body ◽  
Structural Units ◽  
Symmetric Tilt ◽  
Vacancy Model ◽  
Body Potential ◽  
Misorientation Angles

The computer simulation methods have been applied to calculate structure and energy of symmetric tilt grain boundaries (GB) with the misorientation axes [110] and [111]. The calculations have been carried out with the use of the structural-vacancy model. The study of the atomic structure has been carried out within the entire range of misorientation angles. The reverse density of coincidence sites in special grain boundaries has amounted Σ≤57. The calculations have been carried out with the use of the Morse pair potential and the Cleri-Rosato many-body potential. When calculated with different potentials, the dependence of GB energy on the misorientation angle has a similar form, and the atomic structure completely coincides. It has been shown that the structure of any GB with the misorientation axes [110] and [111] may be represented by a limited number of basic structural units. All found basic structural units defined as units of A, B, C and D types are based on the structures of special grain boundaries. Such special GBs shall be Σ3(111), Σ3(112), Σ11(113) and Σ9(114) for GBs with the misorientation axis [110], and as regarding GBs with the misorientation axis [111], such special GBs shall be Σ3(112), Σ7(123) and Σ13(134). Ranges of angles within which certain basic structural units are found have been defined.

scholarly journals Evolution of superconductivity in K2−xFe4+ySe5: Spectroscopic studies of X-ray absorption and emission

2019 ◽  
Vol 116 (45) ◽  
pp. 22458-22463
Author(s):  
H. T. Wang ◽  
Anirudha Ghosh ◽  
C. H. Wang ◽  
S. H. Hsieh ◽  
Y. C. Shao ◽  
...  
Keyword(s):  
Nearest Neighbor ◽  
Volume Fraction ◽  
Spectroscopic Studies ◽  
Synthesis Temperature ◽  
Structural Vacancy ◽  
X Ray ◽  
Atomic Structures ◽  
X Ray Scattering ◽  
Superconducting Volume Fraction ◽  
X Ray Absorption

This study investigates the evolution of superconductivity in K2−xFe4+ySe5 using temperature-dependent X-ray absorption and resonant inelastic X-ray scattering techniques. Magnetization measurements show that polycrystalline superconducting (SC) K1.9Fe4.2Se5 has a critical temperature (Tc) of ∼31 K with a varying superconducting volume fraction, which strongly depends on its synthesis temperature. An increase in Fe-structural/vacancy disorder in SC samples with more Fe atoms occupying vacant 4d sites is found to be closely related to the decrease in the spin magnetic moment of Fe. Moreover, the nearest-neighbor Fe–Se bond length in SC samples exceeds that in the non-SC (NS) sample, K2Fe4Se5, which indicates a weaker hybridization between the Fe 3d and Se 4p states in SC samples. These results clearly demonstrate the correlations among the local electronic and atomic structures and the magnetic properties of K2−xFe4+ySe5 superconductors, providing deeper insight into the electron pairing mechanisms of superconductivity.

Determination of Structural Vacancy Densities in Icosahedral Quasicrystals by Slow Positron Beam Technique

2001 ◽  
Vol 363-365 ◽  
pp. 481-483 ◽  
Author(s):  
K. Sato ◽  
H. Uchiyama ◽  
Y. Takahashi ◽  
Ikuzo Kanazawa ◽  
R. Tamura ◽  
...  
Keyword(s):  
Positron Beam ◽  
Structural Vacancy ◽  
Slow Positron ◽  
Icosahedral Quasicrystals ◽  
Beam Technique

scholarly journals Базовые элементы структуры границ зерен наклона. Часть I. Ось разориентации [100]

2020 ◽  
Vol 62 (12) ◽  
pp. 1997
Author(s):  
А.В. Векман ◽  
Б.Ф. Демьянов
Keyword(s):  
Grain Boundaries ◽  
Misorientation Angle ◽  
Pair Potential ◽  
Structural Vacancy ◽  
Energy Curve ◽  
Electron Microscopic ◽  
Structural Units ◽  
Resolution Electron ◽  
Body Potential ◽  
Misorientation Angles

The computer simulation methods have been applied to calculate structure and energy of symmetric tilt grain boundaries with the misorientation axis [100]. The calculations have been carried out with the use of the structural-vacancy model previously developed by the authors. The misorientation angles of grain boundaries of common type have varied from 0º up to 90º while the increment has amounted 1º. The reverse density of coincidence sites in special grain boundaries has amounted Σ ≤ 53. The calculations have been carried out with the use of the Morse pair potential and the Cleri-Rosato many-body potential. It is shown that the dependence of the energy of grain boundaries on the misorientation angle when calculated with different potentials has a similar form, and their structure does not depend on the choice of potential and is in good agreement with high-resolution electron microscopic images. Only one special grain boundary is distinguished on the energy curve which is Σ5(013). It has been found that the structure grain boundaries may be represented by a limited number of atomic groups that have been named basic structural units. The structure of low-angle grain boundaries with the misorientation angle less than 8º is described by alternation of basic structural units of D types and ideal crystal, while the structure of low-angle grain boundaries with the misorientation angle ranging from 8º up to 13º is described by alternation of structural units of C and D types, from 14º up to 23º – B and C types. High-angle grain boundaries in the range of misorientation angles from 24º up to 37º contain only of basic structural units of B types, from 38º to 50º – A and B, more than 50º – only A.

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