Understanding The Nb-Ti-A1 System: First Principles Calculations

1994 ◽  
Vol 364 ◽  
Author(s):  
Michael J. Mehl
Keyword(s):  
High Temperature ◽  
Bulk Modulus ◽  
Total Energy ◽  
Crystal Structures ◽  
Lattice Constant ◽  
Density Of States ◽  
First Principles ◽  
First Principles Calculations ◽  
Electronic Density ◽  
Cubic Phases

AbstractThe discovery of ductile cubic phases in the Nb-Ti-Al system has led to increased study of these high-temperature intermetallics. I have performed first-principles calculations for ordered crystal structures in this system, paying particular attention to the Nb7Ti7Al2 structure. Somewhat surprisingly, the electronic density of states, lattice constant, and bulk modulus are nearly independent of the ordering of these materials, even though the changes in the total energy are significant.

Electronic Structure vs Phase in Al3V

1988 ◽  
Vol 141 ◽  
Author(s):  
J.-H. Xu
Keyword(s):  
Electronic Structure ◽  
Bulk Modulus ◽  
Total Energy ◽  
Crystal Structures ◽  
Lattice Constant ◽  
Density Of States ◽  
Phase Stability ◽  
Local Density ◽  
Young Modulus ◽  
Good Agreement

AbstractThe electronic structure of Al3V vs its two different crystal structures (DO22 and Ll2) were investigated using local density total energy approach. The calculated results of the total energy showed that in Al3V the tetragonal DO22 phase is energetically favored as compared to the cubic Ll2 phase, the total energy in the former case is about 60 mRy/F.U. lower than that in the later case. The calculated lattice constant (a=3.72 Å, c=8.20 Å) is in fairly good agreement with experiment (a=3.778 Å, c=8.326 Å),and the bulk modulus (1.3 Mbar) is comparable with the experimental Young modulus (150 GPa) for Al3Ti. Furthermore, it is interesting to note that the density of states at EF in the tetragonal DO22 phase (0.14 states/eV-F.U.) is about one order magnitude smaller than that in the Ll2 phase (2.89 states/eV-F.U.). The electronic structure of Al3V seems to be fairly satisfactory in explaining its phase stability.

First-Principles Calculations of Elastic Properties of HoBi and ErBi

2013 ◽  
Vol 664 ◽  
pp. 672-676
Author(s):  
De Ming Han ◽  
Gang Zhang ◽  
Li Hui Zhao
Keyword(s):  
Shear Modulus ◽  
Physical Properties ◽  
Bulk Modulus ◽  
Elastic Properties ◽  
Lattice Constant ◽  
Elastic Constants ◽  
First Principles ◽  
Energy Band ◽  
First Principles Calculations ◽  
Future Work

We present first-principles investigations on the elastic properties of XBi (X=Ho, Er) compounds. Basic physical properties, such as lattice constant, elastic constants (Cij), isotropic shear modulus (G), bulk modulus (B), Young’s modulus (Y), Poisson’s ratio (υ), and Anisotropy factor (A) are calculated. The calculated energy band structures show that the two compounds possess semi-metallic character. We hope that these results would be useful for future work on two compounds.

Chemical Bonding and Pseudogap in Zn- and Cd-based Compounds with Complex Hexagonal Structures

2003 ◽  
Vol 805 ◽  
Author(s):  
Y. Ishii ◽  
K. Nozawa ◽  
T. Fujiwara
Keyword(s):  
Fermi Level ◽  
Density Of States ◽  
Chemical Bonding ◽  
First Principles ◽  
Electronic Structures ◽  
Unit Cell ◽  
First Principles Calculations ◽  
Electronic Density ◽  
Electronic Density Of States ◽  
Crystal Orbital

ABSTRACTElectronic structures of hexagonal Zn-Mg-Y and Cd58Y13 compounds are studied by first-principles calculations. Both of the systems show deep pseudogap in the electronic density of states near the Fermi level and considered to be stabilized electronically. To illustrate bonding nature of electronic wavefunctions, the crystal orbital Hamilton population (COHP) is calculated for neighboring pairs of atoms in the unit cell. It is found that the bonding nature is changed from bonding to anti-bonding almost exactly at the Fermi level for Zn-Zn and Cd-Cd bonds. On the contrary, for Zn/Cd-Y bonds, both of the states below and above the pseudogap behave as bonding ones. Possible effects of the p-d hybridization are discussed.

STRUCTURAL, ELECTRONIC, THERMODYNAMIC AND THERMAL PROPERTIES OF ZINC-BLENDE InP, InAs AND THEIR InAsx P1-x TERNARY ALLOYS VIA FIRST PRINCIPLES CALCULATIONS

2013 ◽  
Vol 27 (27) ◽  
pp. 1350166 ◽  
Author(s):  
O. NEMIRI ◽  
S. GHEMID ◽  
Z. CHOUAHDA ◽  
H. MERADJI ◽  
F. EL HAJ HASSAN
Keyword(s):  
Thermal Properties ◽  
Bulk Modulus ◽  
Band Gap ◽  
Lattice Constant ◽  
First Principles ◽  
Density Functional ◽  
Experimental Studies ◽  
Ternary Alloys ◽  
Full Potential ◽  
First Principles Calculations

First-principles calculations are performed to study the structural, electronic, thermodynamic and thermal properties of the InP and InAs bulk materials and InAs x P 1-x ternary alloys using the full potential-linearized augmented plane wave method (FP-LAPW) within the density functional theory (DFT). The dependence of the lattice constant, bulk modulus, band gap, Debye temperature, heat capacity and mixing entropy on the composition x was analyzed. The lattice constant for InAs x P 1-x alloys exhibits a marginal deviation from the Vegard's law. A large deviation of the bulk modulus from linear concentration dependence (LCD) was observed for our alloys. We found that the composition dependence of the energy band gap is almost linear by using the mBJ and EV-GGA approximations. The microscopic origins of the gap bowing were explained and detailed by using the approach of Zunger and co-workers. Furthermore, the calculated phase diagram shows a miscibility gap for these alloys with a high critical temperature. Thermal effects on some macroscopic properties of InAs x P 1-x alloys are predicted using the quasi-harmonic Debye model, in which the phononic effects are considered. This is the first quantitative theoretical prediction of the thermal properties of the InAs x P 1-x alloys, and we still expect the confirmation of experimental studies.

First-principles study of the vacancy and layer defects in Ti3SiC2

2020 ◽  
Vol 34 (20) ◽  
pp. 2050198
Author(s):  
Jian-Rong Zhang ◽  
Wei-Ming Liu ◽  
Li-Dong Ma ◽  
Qion Yang ◽  
Yan-Wei Chen ◽  
...  
Keyword(s):  
High Temperature ◽  
Electronic Properties ◽  
Lattice Constant ◽  
First Principles ◽  
Formation Energy ◽  
Nuclear Materials ◽  
First Principles Calculations ◽  
Slight Effect ◽  
Suitable Candidate ◽  
Formation Energies

First-principles calculations are performed to study the effects of defect on the structure and electronic properties of Ti3SiC2. The calculations show that the formation energy of Si vacancy is minimal compared with the Ti or C vacancies in Ti3SiC2. The defects of Si layer also can be formed under high-temperature or irradiation environments. The C-layers or Ti-layers are almost impossible to form. If the Si vacancy or Si layers are formed, they prefer to be substituted by the O and H atoms to form the MXene structure, and the unit cell of Ti3SiC2 lattice constant decreases in c-direction. However, it has quite slight effect on electronic properties of Ti3SiC2. The He impurities are almost impossible to occupy the Si vacancies, because the formation energy are 50.860 eV for one layer of Si atoms substituted by the He atoms. This type of defect leads to the lattice constant of Ti3SiC2 in c-direction increasing considerably. Therefore, Ti3SiC2 is a suitable candidate for nuclear materials because of the high-formation energies of He impurities under irradiation environment.

The estimation of energy and elastic properties of TiAlNb materials based on results of first principles calculations

2021 ◽  
Vol 2021 (3) ◽  
pp. 55-65
Author(s):  
L. Ovsiannikova ◽  
◽  
N. Rozhenko ◽  
Keyword(s):  
Bulk Modulus ◽  
Elastic Properties ◽  
First Principles ◽  
Density Functional ◽  
Cluster Structure ◽  
Cohesion Energy ◽  
First Principles Calculations ◽  
Electronic Density ◽  
Β Phase ◽  
Bcc Structure

The results of research of isolated TiAlNb clusters are presented. The models of isolated clusters of 27, 59, 65 atoms in size which is fragments of the bcc structure have been constructed. The models stoichiometry imitate α-, γ-, α+γ- and β-phase TiAlNb alloys. The structural, cohesive and electronic properties of these clusters have been investigated within the framework of electronic density functional theory with PBE0 functional with a set of MINI basis functions with application of Gaussian'03 and GAMESS software packages. It was found that upon transition of the cluster structure from the α- to the β-phase, the cohesion energy increases and the crystal lattice period decreases. This corresponds to an increase in the values of the structure strength and density. For the calculation of the bulk modulus were utilized value of changes in energy and volume of cluster, got in research. The bulk modulus of the isolated β-phase TiAlNb cluster is predicted. This bulk modulus near to 142.4 GPa. The result was extended to volumetric structures. The investigation showed that bulk modulus of Ti2AlNb materials near to 163.6 GPa. Comparison of calculation results with experimental values of elastic moduli of materials with similar structure and composition is carried out. The comparison revealed the agreement between the calculated values and the results of experiments. A method is proposed for evaluating the elastic properties of TiAlNb alloys based on the results of first principles calculations. Keywords: cluster, aluminide titanium, bulk modulus, computer material science.

scholarly journals The Effect of Point Defects on the Electronic Density of States of ScMN2-Type (M = V, Nb, Ta) Phases

2019 ◽  
Vol 4 (3) ◽  
pp. 70 ◽  
Author(s):  
Robert Pilemalm ◽  
Sergei Simak ◽  
Per Eklund
Keyword(s):  
Density Of States ◽  
Point Defects ◽  
First Principles ◽  
Density Functional ◽  
First Principles Calculations ◽  
Electronic Density ◽  
Functional Theory ◽  
Occupied State ◽  
Narrow Bandgap ◽  
Bandgap Semiconductors

ScMN2-type (M = V, Nb, Ta) phases are layered materials that have been experimentally reported for M = Ta and Nb. They are narrow-bandgap semiconductors with potentially interesting thermoelectric properties. Point defects such as dopants and vacancies largely affect these properties, motivating the need to investigate these effects. In particular, asymmetric peak features in the density of states (DOS) close to the highest occupied state is expected to increase the Seebeck coefficient. Here, we used first principles calculations to study the effects of one vacancy or one C, O, or F dopant on the DOS of the ScMN2 phases. We used density functional theory to calculate formation energy and the density of states when a point defect is introduced in the structures. In the DOS, asymmetric peak features close to the highest occupied state were found as a result of having a vacancy in all three phases. Furthermore, one C dopant in ScTaN2, ScNbN2, and ScVN2 implies a shift of the highest occupied state into the valence band, while one O or F dopant causes a shift of the highest occupied state into the conduction band.

FIRST PRINCIPLES CALCULATIONS OF THE ADSORPTION OF GROUP III METALS ON Si(001) AT HIGH TEMPERATURE

2002 ◽  
Vol 09 (05n06) ◽  
pp. 1641-1644 ◽  
Author(s):  
J. COTZOMI-PALETA ◽  
GREGORIO H. COCOLETZI ◽  
NOBORU TAKEUCHI
Keyword(s):  
High Temperature ◽  
Total Energy ◽  
Surface Reconstruction ◽  
High Temperatures ◽  
First Principles ◽  
Structural Parameters ◽  
First Principles Calculations ◽  
Atomic Configuration ◽  
Energy Calculations ◽  
Group Iii

First principles total energy calculations are performed to investigate the Si(001)-(3 × 4) reconstruction induced by the adsorption of group III metals (Ga, Al and In) when deposited at high temperatures. We have considered different models in our study and we have found that the pyramid-like structure proposed by Bunk et al. for In on Si(001) yields the most stable atomic configuration in all cases. We present a detailed description of this surface reconstruction, and compare the structural parameters for Al, Ga and In.

Defect Complexes and Non-Equilibrium Processes Underlying the P-Type Doping of GaN

1998 ◽  
Vol 537 ◽  
Author(s):  
Fernando A. Reboredo ◽  
Sokrates T. Pantelides
Keyword(s):  
High Temperature ◽  
Experimental Evidence ◽  
First Principles ◽  
Final Anneal ◽  
First Principles Calculations ◽  
Defect Complexes ◽  
Equilibrium Processes ◽  
Open Questions ◽  
High Temperature Anneal ◽  
P Type

AbstractIt is well known that hydrogen plays a key role in p-type doping of GaN. It is believed that H passivates substitutional Mg during growth by forming a Mgs-N-Hi complex; in subsequent annealing, H is removed, resulting in p-type doping. Several open questions have remained, however, such as experimental evidence for other complexes involving Mg and H and difficulties in accounting for the relatively high-temperature anneal needed to remove H. We present first principles calculations in terms of which we show that the doping process is in fact significantly more complex. In particular, interstitial Mg plays a major role in limiting p-type doping. Overall, several substitutional/interstitial complexes form and can bind H, with vibrational frequencies that account for hitherto unidentified observed lines. We predict that these defects, which limit doping efficiency, can be eliminated by annealing in an atmosphere of H and N prior to the final anneal that removes H.

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