Phase Stability and Role of Ternary Additions on Electronic and Mechanical Properties of Aluminum Intermetallics

1990 ◽  
Vol 213 ◽  
Author(s):  
A.J. Freeman ◽  
T. Hong ◽  
W. Lin ◽  
Jian-Hua Xu
Keyword(s):  
Mechanical Properties ◽  
Phase Stability ◽  
First Principles ◽  
Local Density ◽  
Electronic Charge ◽  
Intermetallic Alloys ◽  
Phase Boundaries ◽  
Bonding Properties ◽  
Ternary Additions

ABSTRACTFirst principles total energy local density method have addressed the problems of (i) bonding, cohesion and phase stability and (ii) the role of ternary additions, anti-phase boundaries (APB's) and other faults in determining the structural, electronic and mechanical properties of aluminum intermetallic alloys. A key goal has been to attempt to understand, at the electronic level, fundamental quantities that may be related to the crucial brittleness vs. ductility issue in high temperature Ni and Ti and other aluminides. Other contrasts between observed ductility properties of related systems (e.g., NiAl and RuAl) are related to their differing electronic and bonding properties, particularly the nature of p-d hybridization and the directional properties of their electronic charge distrubutions - especially for states near the Fermi energy.

First-Principles Study of Electronic and Elastic Properties of Hexagonal Layered Crystal MoS2 Under Pressure

2015 ◽  
Vol 70 (7) ◽  
pp. 529-537 ◽  
Author(s):  
Jiao-Nan Yuan ◽  
Yan Cheng ◽  
Xiu-Qing Zhang ◽  
Xiang-Rong Chen ◽  
Ling-Cang Cai
Keyword(s):  
Elastic Properties ◽  
First Principles ◽  
Local Density ◽  
Experimental Result ◽  
Partial Density ◽  
Electronic Charge ◽  
Layered Crystal ◽  
Bonding Properties ◽  
Valence Bands ◽  
Indirect Band Gap

AbstractThe structural, electronic, and elastic properties of hexagonal layered crystal MoS2 under pressure are investigated using first-principles calculations within the local density approximation (LDA). The calculated lattice parameters a0, c0, and cell volume V0 of MoS2 are in good agreement with the available experimental data. Our calculations show that MoS2 is an indirect band gap semiconductor and there is a vanishing anisotropy in the rate of structural change at around 25 GPa, which is consistent with the experimental result. We also analyse the partial density of states (PDOS) of MoS2 at 0 and 14 GPa, which indicate that the whole valence bands of MoS2 are mainly composed by the Mo-4d and S-3s states at 0 GPa, while they are mainly composed by the Mo-4p, Mo-4d, and S-3p states at 14 GPa. The electronic charge density difference maps show the covalent characteristic of Mo–S, and the bonding properties of MoS2 are investigated by using the Mulliken overlap population. In addition, the elastic constants Cij, bulk modulus B, shear modulus G, Young’s modulus Y, the Debye temperature ΘD, and hardness H of MoS2 are also obtained successfully. It is found that they all increase monotonically with the increasing pressure.

First Principles Study of Phase Stability in The Al-Ti System

1990 ◽  
Vol 186 ◽  
Author(s):  
M. Asta ◽  
M. Sluiter ◽  
Prabhakar P. Singh ◽  
D. de Fontaine ◽  
T. Hong ◽  
...  
Keyword(s):  
Phase Stability ◽  
First Principles ◽  
Tetragonal Distortion ◽  
Low Density ◽  
First Principles Study ◽  
Ternary Additions ◽  
Very High

Due to its technological importance, the Al-Ti system has received much attention lately. For example, TiAl3 (as well as TiAl) has a low density and very high elevatedtemperature strength. However, this compound forms in the tetragonal D022 structure which has low ductility. Recent studies [1,2] have tried to understand the role of tetragonal distortion and the effect of ternary additions [3] in stablizing the D022 relative to the L12.

First-principles study of phase stability, electronic and mechanical properties of plutonium sub-oxides

2019 ◽  
Vol 21 (30) ◽  
pp. 16818-16829 ◽  
Author(s):  
P. S. Ghosh ◽  
A. Arya
Keyword(s):  
Mechanical Properties ◽  
Density Functional Theory ◽  
Phase Stability ◽  
First Principles ◽  
Density Functional ◽  
Functional Theory ◽  
First Principles Study ◽  
Hubbard Parameter ◽  
Formation Energies

Formation energies of PuO2, α-Pu2O3 and sub-oxides PuO2−x (0.0 < x < 0.5) are determined using density functional theory employing generalised gradient approximation corrected with an effective Hubbard parameter.

The Role of Phase Stability in Ductile, Ordered B2 Intermetallics

2006 ◽  
Vol 980 ◽  
Author(s):  
James R. Morris ◽  
Yiying Ye ◽  
Maja Krcmar ◽  
Chong Long Fu
Keyword(s):  
Phase Stability ◽  
First Principles ◽  
Tensile Ductility ◽  
Stacking Faults ◽  
Low Energy ◽  
First Principles Calculations ◽  
Phase Competition ◽  
Transformation Pathway ◽  
Shape Memory Materials

AbstractWe discuss the underlying atomistic mechanism for experimentally observed large tensile ductility in various strongly ordered B2 intermetallic compounds. First-principles calculations demonstrate that all of the compounds exhibit little energy differences between the B2, B27 and B33 phases. These calculations relate observations of ductility in YAg, YCu and ZrCo to shape-memory materials including NiTi. One transformation pathway between the B2 and B33 phases establishes a connection between this phase competition, and stacking faults on the {011}B2 plane. The low energy of such a stacking fault will lead to splitting of the b=<100> dislocations into b/2 partials, observed in ZrCo, TiCo, and in the B19' phase of NiTi. Calculations demonstrate that this pathway is competitive with the traditional pathway for NiTi.

Electronic and Optical Properties of Si/SiO2 Superlattices from First Principles: Role of Interfaces.

2001 ◽  
Vol 677 ◽  
Author(s):  
Pierre Carrier ◽  
Gilles Abramovici ◽  
Laurent J. Lewis ◽  
M. W. C. Dharma-wardana
Keyword(s):  
Optical Properties ◽  
First Principles ◽  
Energy Gap ◽  
Local Density ◽  
Interband Transition ◽  
Theoretical Research ◽  
Slab Thickness ◽  
Full Potential ◽  
Wave Method

ABSTRACTThe observation of intense luminescence in Si/SiO2 superlattices (SLs) has lead to new theoretical research on silicon-based materials. We have performed first-principles calculations using three Si/SiO2 SL models in order to examine the role of interfaces on the electronic structure and optical properties. The first two models are derived directly from crystalline structures and have simple interfaces. These models have been studied using the full-potential, linearized-augmented-plane-wave method, in the local-density-approximation (LDA). The optical absorption within the interband transition theory (excluding excitonic effects) have been deduced. The Si(001)-SiO2 interface structure is shown to affect the optical behaviour. Following these observations, we have considered a more realistic, fully-relaxed model. The projector-augmented-wave method under the LDA is used to perform the structural relaxation as well as band structure and optical calculations. The role of confinement on the energy gap is studied by inserting additional silicon slabs into the supercell. Direct energy gaps are observed and the energy gap is found to decrease with increasing silicon slab thickness, as observed experimentally. The role of the interface has been considered in more details by studying the contribution to the energy gap of Si atoms having different oxidation patterns; partially oxidized Si atoms at the interface, as well as Si atoms inside the Si layer, are shown to contribute to the transitions at the energy gap.

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