A Computational Study of Oxygen Contamination in Sb2Te3

2006 ◽  
Vol 918 ◽  
Author(s):  
John Earl Boyd ◽  
Arthur Edwards ◽  
Andrew C. Pineda
Keyword(s):  
Density Functional ◽  
Defect Formation ◽  
Computational Study ◽  
Low Concentrations ◽  
Substitutional Defects ◽  
High Concentrations ◽  
Single Oxygen Atom ◽  
Crystalline System ◽  
Single Oxygen ◽  
Formation Energies

AbstractWe present first principles electronic structure calculations of oxygen substitutional defects in the Sb2Te3 layered crystalline system and a model of amorphous Sb2Te3 using density functional theory (DFT). Our calculated formation energies for oxygen substitutional defects at Sb sites are above 2 eV, so most of our results are on the Sb2Te3-xOx [x = .0074 - .20] system, where one of two inequivalent Te sites are instead occupied by a single oxygen atom with formation energies between -1.2 eV and .2 eV. Defect formation energies for the system show a preference for oxygen atoms on the Te1 site at low concentrations that switches to the Te2 site at high concentrations at approximately 6 atomic percent. In agreement with experiment, we find that oxygen does widen the band gap, even at relatively low concentrations.

Computational study of Mg insertion into amorphous silicon: advantageous energetics over crystalline silicon for Mg storage

2013 ◽  
Vol 1540 ◽  
Author(s):  
Fleur Legrain ◽  
Oleksandr I. Malyi ◽  
Teck L. Tan ◽  
Sergei Manzhos
Keyword(s):  
Density Functional ◽  
Nearest Neighbor ◽  
Defect Formation ◽  
Crystalline Silicon ◽  
Computational Study ◽  
Binding Energies ◽  
Functional Theory ◽  
Wide Range ◽  
Insertion Sites ◽  
Formation Energies

ABSTRACTWe show in a theoretical density functional theory study that amorphous Si (a-Si) has more favorable energetics for Mg storage compared to crystalline Si (c-Si). Specifically, Mg and Li insertion is compared in a model a-Si simulation cell. Multiple sites for Mg insertion with a wide range of binding energies are identified. For many sites, Mg defect formation energies are negative, whereas they are positive in c-Si. Moreover, while clustering in c-Si destabilizes the insertion sites (by about 0.1/0.2 eV per atom for nearest-neighbor Li/Mg), it is found to stabilize some of the insertion sites for both Li (by up to 0.27 eV) and Mg (by up to 0.35 eV) in a-Si. This could have significant implications on the performance of Si anodes in Mg batteries.

A complete ab initio thermodynamic and kinetic catalogue of the defect chemistry of hematite α-Fe2O3, its cation diffusion, and sample donor dopants

2021 ◽  
Author(s):  
Shehab Shousha ◽  
Sarah Khalil ◽  
Mostafa Youssef
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Defect Formation ◽  
Defect Chemistry ◽  
Cation Diffusion ◽  
Functional Theory ◽  
Migration Barriers ◽  
Hubbard U ◽  
And Migration ◽  
Formation Energies

This paper studies comprehensively the defect chemistry and cation diffusion in α-Fe2O3. Defect formation energies and migration barriers are calculated using density functional theory with a theoretically calibrated Hubbard U...

DEFECT FORMATION AND MAGNETIC PROPERTIES OF Co-DOPED ZnO NANOWIRES

NANO ◽  
2013 ◽  
Vol 08 (02) ◽  
pp. 1350021 ◽  
Author(s):  
LI BIN SHI ◽  
GUO QUAN QI ◽  
YING FEI
Keyword(s):  
Magnetic Properties ◽  
Density Functional ◽  
Defect Formation ◽  
Density Functional Method ◽  
Zno Nanowires ◽  
Generalized Gradient ◽  
Surface Sites ◽  
Doped Zno ◽  
Formation Energies ◽  
Co Doped

The defect formation energies and magnetic properties in Co -doped ZnO nanowires (NWs) are studied using the first-principle density functional method within the generalized gradient approximation (GGA) and GGA + U schemes. It is found that Co impurity has lower formation energies in the surface sites, indicating that Co impurity occupies preferably surface sites of NWs. Ferromagnetic (FM) and antiferromagnetic (AFM) coupling are investigated by GGA and GGA + U methods. The results show that the AFM coupling in energy is lower than the FM coupling, which indicates that AFM coupling is more stable. The magnetic properties can be mediated by the vacancies [ VO(B) and VZn(B) ] and interstitials [ IZn(oct) ]. The stability of the FM and AFM can be explained by the Co 3d energy level coupling.

scholarly journals Kinetic Monte Carlo Simulation of Oxygen Diffusion in Ytterbium Disilicate

MRS Advances ◽  
2016 ◽  
Vol 1 (17) ◽  
pp. 1203-1208 ◽  
Author(s):  
Brian S. Good
Keyword(s):  
Monte Carlo ◽  
High Temperature ◽  
Oxygen Diffusion ◽  
Density Functional ◽  
Defect Formation ◽  
Kinetic Monte Carlo ◽  
Interstitial Oxygen ◽  
Temperature Oxidation ◽  
Electron Volt ◽  
Formation Energies

ABSTRACTYtterbium disilicate is of interest as a potential environmental barrier coating for aerospace applications, notably for use in next generation jet turbine engines. In such applications, the transport of oxygen and water vapor through these coatings to the ceramic substrate is undesirable if high temperature oxidation is to be avoided. In an effort to understand the diffusion process in these materials, we have performed kinetic Monte Carlo simulations of vacancy-mediated and interstitial oxygen diffusion in Ytterbium disilicate. Oxygen vacancy and interstitial site energies, vacancy and interstitial formation energies, and migration barrier energies were computed using Density Functional Theory. We have found that, in the case of vacancy-mediated diffusion, many potential diffusion paths involve large barrier energies, but some paths have barrier energies smaller than one electron volt. However, computed vacancy formation energies suggest that the intrinsic vacancy concentration is small. In the case of interstitial diffusion, migration barrier energies are typically around one electron volt, but the interstitial defect formation energies are positive, with the result that the disilicate is unlikely to exhibit experience significant oxygen permeability except at very high temperature.

scholarly journals The Effect of Defect Disorder on the Electronic Structure of Rutile TiO2-x

2006 ◽  
Vol 251-252 ◽  
pp. 1-12 ◽  
Author(s):  
Faruque M. Hossain ◽  
Graeme E. Murch ◽  
L. Sheppard ◽  
Janusz Nowotny
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Point Defects ◽  
Density Functional ◽  
Defect Formation ◽  
Energy Levels ◽  
Defect Energy ◽  
Defect Disorder ◽  
Effect Of Oxygen ◽  
Formation Energies

The purpose of this work is to study the effect of bulk point defects on the electronic structure of rutile TiO2. The paper is focused on the effect of oxygen nonstoichiometry in the form of oxygen vacancies, Ti interstitials and Ti vacancies and related defect disorder on the band gap width and on the local energy levels inside the band gap. Ab initio density functional theory is used to calculate the formation energies of such intrinsic defects and to detect the positions of these defect induced energy levels in order to visualize the tendency of forming local mid-gap bands. Apart from the formation energy of the Ti vacancies (where experimental data do not exist) our calculated results of the defect formation energies are in fair agreement with the experimental results and the defect energy levels consistently support the experimental observations. The calculated results indicate that the exact position of defect energy levels depends on the estimated band gap and also the charge state of the point defects of TiO2.

scholarly journals Ab Initio Study of MgTe Self-Interstitial (Mgi and Tei): A Wide Band Gap Semiconductor

2017 ◽  
Vol 16 ◽  
pp. 47-51
Author(s):  
Emmanuel Igumbor ◽  
Ezekiel Omotoso ◽  
Walter Ernst Meyer
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Defect Formation ◽  
Local Density ◽  
Wide Band ◽  
Shallow Donor ◽  
Generalized Gradient ◽  
Wide Band Gap ◽  
Functional Theory ◽  
Formation Energies

We present results of defect formation energies and charge state thermodynamic transition levels of Mg and Te interstitials in MgTe wurzite structure. We use the generalized gradient approximation and local density approximation functionals in the framework of density functional theory for all calculations. The formation energies of the Mg and Te interstitials in MgTe for both the tetrahedral and hexagonal configurations were obtained. The Mg and Te interstitials in MgTe depending on the functional, introduced transition state levels that are either donor or acceptor within the band gap of the MgTe. The Te interstitial exhibit charge states controlled metastability, negative-U and DX centre properties. The Mg interstitial acts as deep or shallow donor and there is no evidence of acceptor levels found for the Mg interstitial.

scholarly journals The Conundrum of Relaxation Volumes in First-Principles Calculations of Charged Defects in UO2

2019 ◽  
Vol 9 (24) ◽  
pp. 5276 ◽  
Author(s):  
Anuj Goyal ◽  
Kiran Mathew ◽  
Richard G. Hennig ◽  
Aleksandr Chernatynskiy ◽  
Christopher R. Stanek ◽  
...  
Keyword(s):  
Density Functional ◽  
Defect Formation ◽  
Charged Defect ◽  
Functional Theory ◽  
Neutral Material ◽  
Defect Reactions ◽  
Neutral Defect ◽  
Charged Defects ◽  
Formation Energies ◽  
Defect Relaxation

The defect relaxation volumes obtained from density-functional theory (DFT) calculations of charged vacancies and interstitials are much larger than their neutral counterparts, seemingly unphysically large. We focus on UO2 as our primary material of interest, but also consider Si and GaAs to reveal the generality of our results. In this work, we investigate the possible reasons for this and revisit the methods that address the calculation of charged defects in periodic DFT. We probe the dependence of the proposed energy corrections to charged defect formation energies on relaxation volumes and find that corrections such as potential alignment remain ambiguous with regards to its contribution to the charged defect relaxation volume. We also investigate the volume for the net neutral defect reactions comprising individual charged defects, and find that the aggregate formation volumes have reasonable magnitudes. This work highlights the issue that, as is well-known for defect formation energies, the defect formation volumes depend on the choice of reservoir. We show that considering the change in volume of the electron reservoir in the formation reaction of the charged defects, analogous to how volumes of atoms are accounted for in defect formation volumes, can renormalize the formation volumes of charged defects such that they are comparable to neutral defects. This approach enables the description of the elastic properties of isolated charged defects within an overall neutral material.

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