Structure and Stability of Grain Boundaries in Molybdenum with Segregated Carbon Impurities

1999 ◽  
Vol 578 ◽  
Author(s):  
R. Janisch ◽  
T. Ochs ◽  
A. Merkle ◽  
C. Elsässer
Keyword(s):  
Ab Initio ◽  
Grain Boundaries ◽  
Density Functional ◽  
Local Density ◽  
Structural Parameters ◽  
Carbide Phases ◽  
Carbon Impurities ◽  
Transmission Electron ◽  
Local Density Functional Theory ◽  
Symmetrical Tilt

AbstractThe segregation of interstitial impurities to symmetrical tilt grain boundaries (STGB) in bodycentered cubic transition metals is studied by means of ab-initio electronic-structure calculations based on the local density functional theory (LDFT). Segregation energies as well as changes in atomic and electronic structures at the ΣE5 (310) [001] STGB in Mo caused by segregated interstitial C atoms are investigated. The results are compared to LDFT data obtained previously for the pure Σ5 (310) [001] STGB in Mo. Energetic stabilities and structural parameters calculated ab initio for several crystalline Molybdenum Carbide phases with cubic, tetragonal or hexagonal symmetries and different compositions, MoCx, are reported and compared to recent high-resolution transmission electron microscopy (HRTEM) observations of MoCx, intergranular films and precipitates formed by C segregation to a Σ5 (310) [001] STGB in a Mo bicrystal.

Ab-Initio Determination of the Atomic Structure of Symmetrical Tilt Grain Boundaries in BCC Transition Metals

1997 ◽  
Vol 492 ◽  
Author(s):  
C. Elsässer ◽  
O. Beck ◽  
T. Ochs ◽  
B. Meyer
Keyword(s):  
Transition Metals ◽  
Grain Boundary ◽  
Ab Initio ◽  
Grain Boundaries ◽  
Density Functional ◽  
Local Density ◽  
High Symmetry ◽  
Many Body ◽  
Local Density Functional Theory ◽  
Symmetrical Tilt

ABSTRACTAtomistic simulations of grain-boundary structures in body-centered cubic transition metals have revealed that angle-dependent contributions to interatomic interactions are essential. Unfortunately, the results of presently available empirical many-body potentials are not yet always sufficiently reliable for quantitative theoretical predictions of grain-boundary structures, which are consistent with experimental observations, e.g. by high-resolution transmission electron microscopy.Ab-initio electronic-structure calculations based on the local-density-functional theory offer the possibility to determine accurately the microscopic structures of special, high-symmetry grain boundaries, which can be used as data bases for the improvement of empirical many-body potentials. Such ab-initio calculations, with a mixed-basis pseudopotential method and grain-boundary supercells, are presented for Σ5 (310) [001] 36.87° symmetrical tilt grain boundaries in Niobium and Molybdenum.

Hydrogen Passivated Carbon Acceptors in GaAs and AlAs: no Evidence for Carbon Donors

1993 ◽  
Vol 325 ◽  
Author(s):  
B. R. Davidson ◽  
R. C. Newman ◽  
R. E. Pritchard ◽  
T. J. Bullough ◽  
T. B. Joyce ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Infrared Absorption ◽  
Density Functional ◽  
Local Density ◽  
Absorption Lines ◽  
Functional Theory ◽  
Local Density Functional Theory ◽  
Local Density Functional

AbstractGaAs and AlAs layers grown by CBE and doped with either 12C or 13C have been passivated with hydrogen or deuterium. Infrared absorption lines due to hydrogen stretch modes, symmetric A1 modes and “carbon-like” E modes of H-CAs and D-CAs pairs have been assigned for both isotopes in both hosts. Comparisons have been made with new ab initio local density functional theory and simple harmonic models. Anticrossing behaviour is found for the two types of coupled E modes in the two hosts. The dynamics of the H-CAs centre are very similar in GaAs and AlAs.

AB-INITIO STUDIES OF DIFFUSION AND GROWTH PHENOMENA ON SEMICONDUCTOR SURFACES

1996 ◽  
Vol 03 (02) ◽  
pp. 1295-1303 ◽  
Author(s):  
EFTHIMIOS KAXIRAS
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Local Density ◽  
Semiconductor Surfaces ◽  
Group Vi ◽  
Functional Theory ◽  
Group V ◽  
Si Substrates ◽  
Local Density Functional Theory ◽  
Reconstructed Surface

We discuss the application of ab-initio quantum-mechanical calculations, based on pseudopotential local-density-functional theory, to diffusion and growth phenomena on semiconductor surfaces. We examine in detail two specific examples: adatom diffusion on the Ge (111) c (2×8) reconstructed surface and surfactant-mediated homoepitaxial growth on Si substrates. In these examples, the combination of results from first-principles calculations and simple simulations helps elucidate complex dynamical phenomena. We also make predictions on the feasibility of using hydrogen as a surfactant on Si substrates, by drawing analogies between the chemical behavior of group-V or group-VI adsorbates and Si-H complexes.

Atomic and Electronic Structure of Boron-Doped Diamond Grain Boundaries Studied by Arhvtem and ab-Initio Calculation

2003 ◽  
Vol 764 ◽  
Author(s):  
Hiroyuki Togawa ◽  
Hideki Ichinose
Keyword(s):  
Ab Initio ◽  
Grain Boundaries ◽  
Ab Initio Calculation ◽  
Structure Model ◽  
Boron Doped Diamond ◽  
Boron Doped ◽  
Transmission Electron ◽  
Diamond Grain ◽  
Electron Energy Loss ◽  
Atomic And Electronic Structure

AbstractAtomic resolution high-voltage transmission electron microscopy and electron energy loss spectroscopy were performed on grain boundaries of boron-doped diamond, cooperated with the ab-initio calculation. Segregated boron in the {112}∑3 boundary was caught by the EELS spectra. The change in atomic structure of the segregated boundary was successfully observed from the image by ARHVTEM. Based on the ARHVTEM image, a segregted structure model was proposed.

scholarly journals Structure and Electrochemical Potential Simulation for the Cathode Material Li1+xV3O8

1997 ◽  
Vol 496 ◽  
Author(s):  
R. Benedek ◽  
M. M. Thackeray ◽  
L. H. Yang
Keyword(s):  
Density Functional ◽  
Structural Information ◽  
Local Density ◽  
Tetrahedral Site ◽  
Low Energy ◽  
Electrochemical Potential ◽  
X Ray Diffraction ◽  
X Ray ◽  
Local Density Functional Theory ◽  
Two Phases

ABSTRACTThe structure and electrochemical potential of monoclinic Li1+xV3O8 were calculated within the local-density-functional-theory framework by use of plane-wave-pseudopotential methods. Special attention was given to the compositions 1+x=1.2 and 1+x=4, for which x-ray diffraction structure refinements are available. The calculated low-energy configuration for 1+x=4 is consistent with the three Li sites identified in x-ray diffraction measurements and predicts the position of the unobserved Li. The location of the tetrahedrally coordinated Li in the calculated low-energy configuration for 1+x=1.5 is consistent with the structure measured by x-ray diffraction for Li1.2V3O8. Calculations were also performed for the two monoclinic phases at intermediate Li compositions, for which no structural information is available. Calculations at these compositions are based on hypothetical Li configurations suggested by the ordering of vacancy energies for Li4V3O8 and tetrahedral site energies in Li1.5V3O8. The internal energy curves for the two phases- cross near 1+x=3. Predicted electrochemical potential curves agree well with experiment.

Ab initio perspective of the 〈110〉 symmetrical tilt grain boundaries in bcc Fe: application of local energy and local stress

2014 ◽  
Vol 49 (11) ◽  
pp. 3980-3995 ◽  
Author(s):  
Somesh Kr. Bhattacharya ◽  
Shingo Tanaka ◽  
Yoshinori Shiihara ◽  
Masanori Kohyama
Keyword(s):  
Ab Initio ◽  
Grain Boundaries ◽  
Local Stress ◽  
Local Energy ◽  
Symmetrical Tilt
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