Cluster Models for Point Defect Structure in La2CuO4+δ

1994 ◽  
Vol 341 ◽  
Author(s):  
Yue Wu ◽  
D. E. Ellis ◽  
T. O. Mason
Keyword(s):  
Electronic Structures ◽  
Defect Structure ◽  
Local Density ◽  
Energy Levels ◽  
Interstitial Oxygen ◽  
Discrete Variational Method ◽  
Densities Of States ◽  
Infinite Crystal ◽  
Oxygen Excess ◽  
Point Defect Structure

AbstractWe report theoretical studies on oxygen excess defect structure of lanthanum cuprate, La2CuO4+δ, using the Local Density formalism. The self-consistent Discrete Variational method has been used to find energy levels, densities of states, charge transfer, wavefunctions and potentials for a fragment consisting of N atoms embedded in the infinite crystal. Various possible interstitial oxygen positions and relative stability have been studied, including the structure suggested by Chaillout, et al. on the basis of neutron diffraction. Calculated electronic structures have been used to predict defect-related spectroscopic consequences.

ACCEPTOR MODULATED DEFECT AND ELECTRONIC STRUCTURES IN FERROELECTRIC LEAD TITANATE: AN AB INITIO STUDY

2008 ◽  
Vol 01 (02) ◽  
pp. 121-126 ◽  
Author(s):  
ZHEN ZHANG ◽  
PING WU ◽  
LI LU ◽  
CHANG SHU
Keyword(s):  
Electronic Structures ◽  
Defect Structure ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Charge Effects ◽  
Isolated Point ◽  
Point Defect Structure ◽  
Domain Pinning

Defects and electronic structures of the aliovalent acceptors substituted lead titanates were studied using density functional theory calculations. Three types of defect structures are identified in 3d transition metal and the group IIB and VB elements substituted systems. Cr substitute and oxygen vacancies are found to be dissociated from each other, forming an isolated point defect structure. In contrast, all other substitutes favor the immobile acceptor–oxygen–vacancy–acceptor defect clusters which weaken the space charge effects by limiting the motions of oxygen vacancies. Furthermore, two distinct defect-cluster structures (along the z direction and in the xy plane, respectively) are observed. We conclude that the defect structure in the xy plane induces head-to-head polarization patterns, which make the domain pinning effects even weaker. The electronic structures due to elements substitutions are also investigated and compared.

scholarly journals Energetics of Oxygen Interstitials in Cr and V

2004 ◽  
Vol 851 ◽  
Author(s):  
Brian S. Good ◽  
Evan Copland
Keyword(s):  
Electronic Structures ◽  
Density Functional ◽  
Fundamental Problem ◽  
Computer Code ◽  
Oxygen Solubility ◽  
Interstitial Oxygen ◽  
Oxide Compound ◽  
Densities Of States ◽  
Bcc Structure ◽  
Total Energies

ABSTRACTDissolved oxygen in group IIIA-VA (Nb, Ti, Zr, Y) based alloys is a fundamental problem, affecting both mechanical properties and oxidation resistance, yet details of the phenomenon are poorly understood. In these alloys, oxygen is more stable dissolved in the metal than as an oxide-compound. In contrast, alloys based on Ni, Fe, Al and Cr exhibit almost no oxygen solubility. To improve the performance of Nb and Ti based alloys it is necessary to understand the differences in oxygen solubility between these two groups of metals. As a first step we considered the energetics of interstitial oxygen in α-V and α-Cr. Both of these metals have a BCC structure, yet the oxygen solubility in V is much higher than that in Cr. We obtain total energies, densities of states and population analyses using the CASTEP plane-wave pseudopotential density functional computer code. The differences in the energetics and electronic structures of the two materials, particularly the partial densities of states associated with the interstitial oxygen, are discussed.

Electronic bonding characteristics of hydrogen in bcc iron: Part I. Interstitials

1996 ◽  
Vol 11 (9) ◽  
pp. 2206-2213 ◽  
Author(s):  
Yoshio Itsumi ◽  
D. E. Ellis
Keyword(s):  
Density Functional ◽  
Local Density ◽  
Lattice Relaxation ◽  
Experimental Result ◽  
Functional Formalism ◽  
Discrete Variational Method ◽  
Bcc Iron ◽  
Bond Strengths ◽  
Bonding Characteristics ◽  
Structure Calculations

Electronic structure calculations were carried out for bcc iron (Fe) clusters with or without hydrogen (H), and also involving a vacancy, using the self-consistent Discrete Variational method (DV-Xα) within the local density functional formalism. Bonding characteristics investigated show the following: (i) Interstitial H notably decreases interatomic Fe–Fe bond strengths, but acts over a small distance (within 0.3 nm). (ii) In the perfect Fe lattice field, interstitial H feels a repulsive force at any site. As a result of lattice relaxation, volume expansion may be expected. (iii) H in combination with a vacancy prefers a position shifted from the octahedral site toward the vacancy. This is fairly consistent with an experimental result.

The Defect Structure of BaTiO3 Thin Films

1993 ◽  
Vol 310 ◽  
Author(s):  
L.A. Wills ◽  
B.W. Wessels
Keyword(s):  
Thin Films ◽  
Cross Section ◽  
Defect Structure ◽  
Oxygen Vacancies ◽  
Vacuum Annealing ◽  
Deep Level ◽  
Energy Levels ◽  
The Other ◽  
Optical Cross Section ◽  
Impurity Defects

AbstractThe defect structure of BaTiO3 thin films grown on (100) Si was examined using transient photocapacitance spectroscopy. The concentration, optical cross section and associated energy levels of both native and impurity defects in as-grown and annealed BaTiO3 films were evaluated. Deep level defects withpeak energies of Ev+1.8, Ev+2.4, Ev+2.7, Ev+3.0-3.1 and Ev+3.2-3.3 eV were observed in the as-grown films. Upon vacuum annealing, the concentration of the traps at Ev+3.0 and Ev+3.2 eV increased while the concentration of the traps at Ev+ 1.8 and Ev+2.4 eV decreased. The levels at Ev+3.0-3.1 and Ev+3.2-3.3 eV are attributed to oxygen vacancies. The other levels are tentatively ascribed to Fe and Fe related defects.

Relation of Phase Stability Boundary to the Fill-Up Bonding States In Ni3V,Co3V and Fe3V

1990 ◽  
Vol 213 ◽  
Author(s):  
W. Lin ◽  
Jian-Hua Xu ◽  
A.J. Freeman
Keyword(s):  
Structural Stability ◽  
Electronic Structures ◽  
Local Density ◽  
Stability Boundary ◽  
The Self ◽  
Orbital Method ◽  
Density Approximation ◽  
Cohesive Properties ◽  
Self Consistent ◽  
Electronic Concentration

ABSTRACTThe electronic structures and cohesive properties of the intermetallics Ni3V, Co3V, and Fe3V in the L12 structure have been studied using the self-consistent total energy linear muffin-tin orbital method based on the local density approximation. The simple rigid-band concept appears to be adequate to explain the structural stability of these compounds. Further,the structural stability of the pseudobinary compounds (Ni,Co,Fe)3V has been investigated based on the rigid-band scheme. The correlation between the electronic concentration and the crystal structure is shown to be related to the fill-up of the bonding states.

A comparative study on the LDA + U and hybrid functional methods on the description of the electronic structure of YTiO3 under high pressure

2009 ◽  
Vol 87 (10) ◽  
pp. 1374-1382 ◽  
Author(s):  
Z. Song ◽  
J. J. Yang ◽  
J. S. Tse
Keyword(s):  
Electronic Structures ◽  
Local Density ◽  
Band Gaps ◽  
Density Approximation ◽  
Hybrid Functional ◽  
Functional Methods ◽  
Mixing Parameters ◽  
Hubbard U ◽  
Hubbard Parameter ◽  
Pressure Analysis

The electronic structures of YTiO3 under pressure have been studied with LDA + U (local density approximation + Hubbard parameter) and hybrid functional methods. From matching the experimental band gaps, the Hubbard U and hybrid functional mixing parameters were determined. It is found that both parameters vary with the pressure. Analysis of the electronic structures indicates that the description of the chemical bonding is also dependent on the method of choice.

Bandfilling and structural stability of trialuminides: YAl3, ZrAl3, and NbAl3

1991 ◽  
Vol 6 (6) ◽  
pp. 1188-1199 ◽  
Author(s):  
Jian-hua Xu ◽  
A.J. Freeman
Keyword(s):  
Transition Metal ◽  
Structural Stability ◽  
Electronic Structures ◽  
Local Density ◽  
Metal Carbides ◽  
Metal Compounds ◽  
Cohesive Properties ◽  
Valence Electrons ◽  
Stable Forms ◽  
Covalent Interactions

The cohesive properties and electronic structures versus the structural stability of transition-metal trialuminides YAl3, ZrAl3, and NbAl3 in their cubic L12, tetragonal DO22, and naturally stable forms (i.e., the DO19 structure for YAl3 and the DO23 structure for ZrAl3) have been investigated using a total energy local-density approach. The variation of structural stability with transition-metal constituent can be simply understood in terms of the bandfilling of the bonding states in the rigid band sense, with the valence electrons gradually filling the bonding states on going from YAl3, ZrAl3 to NbAl3. This leads to a phase transition from the cubic L12 structure (for YAl3) to the tetragonal DO22 structure (for NbAl3). It is argued that this criterion may also apply to explain the variation of the structural stability of other transition-metal compounds (such as transition-metal carbides, nitrides, silicides, etc.) that are dominated by covalent interactions between the transition-metal d and the metalloid p states.

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