First-principles study of deformation-induced phase transformations in Ti–Al intermetallics

2009 ◽  
Vol 24 (5) ◽  
pp. 1662-1666 ◽  
Author(s):  
C.L. Chen ◽  
W. Lu ◽  
L.L. He ◽  
H.Q. Ye
Keyword(s):  
Phase Transformations ◽  
Intermetallic Compounds ◽  
Density Functional ◽  
Structural Phase ◽  
Generalized Gradient ◽  
Theoretical Understanding ◽  
Functional Theory ◽  
Tial Alloys ◽  
The Stability ◽  
Formation Energies

The structural phase stability and electronic properties of the Ti–Al intermetallic compounds were investigated by means of density-functional theory (DFT) calculations in a generalized gradient approximation. Through comparison of the calculated formation energies of the parent and product phases, an in-depth theoretical understanding of the deformation-induced γ ↔ α2 phase transitions observed previously in TiAl alloys was achieved. The formation energy plays an important role in evaluating the feasibility of these phase transformations during plastic deformation of TiAl alloys. In addition, the density of states (DOS) was also calculated and used to analyze the stability of Ti–Al intermetallic compounds. The reasons for the absence of the deformation-induced (DI)-α2 and DI-γ (L12) phases in underformed TiAl alloys were analyzed.

Ab-initio thermodynamic and elastic properties of AlNi and AlNi3 intermetallic compounds

2018 ◽  
Vol 32 (11) ◽  
pp. 1850129 ◽  
Author(s):  
Shahram Yalameha ◽  
Aminollah Vaez
Keyword(s):  
Intermetallic Compounds ◽  
Elastic Properties ◽  
Density Functional ◽  
Full Potential ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Augmented Plane Wave ◽  
Wide Range ◽  
Computational Data ◽  
Linearized Augmented Plane Wave

In this paper, thermodynamic and elastic properties of the AlNi and AlNi3 were investigated using density functional theory (DFT). The full-potential linearized augmented plane-wave (APW) in the framework of the generalized gradient approximation as used as implemented in the Wien2k package. The temperature dependence of thermal expansion coefficient, bulk modulus and heat capacity in a wide range of temperature (0–1600 K) were investigated. The calculated elastic properties of the compounds show that both intermetallic compounds of AlNi and AlNi3 have surprisingly negative Poisson’s ratio (NPR). The results were compared with other experimental and computational data.

scholarly journals Ab Initio Study of MgSe Self-Interstitial (Mgi and Sei)

2015 ◽  
Vol 242 ◽  
pp. 440-446 ◽  
Author(s):  
Emmanuel Igumbor ◽  
Kingsley Obodo ◽  
Water E. Meyer
Keyword(s):  
Transition State ◽  
Density Functional ◽  
Local Density ◽  
Shallow Donor ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Interstitial Defects ◽  
Frame Work ◽  
Formation Energies

We present detailed calculations of formation and thermodynamics transition state energies of Mgiand Seiinterstitial defects in MgSe using generalized gradient approximation (GGA) and local density approximation (LDA) functional in the frame work of density functional theory (DFT). For both LDA and GGA the formation energies of Mgiand Seiare relatively low in all the configurations. The most stable Se interstitial was the tetrahedral (T) configuration having lower formation energy than the decagonal (D) configuration. TheMgiand Seidefect introduced transition state levels that had either donor or acceptor levels within the band gap. Seiacts as a donor or an acceptor and creates levels that were either deep or shallow depending on the configuration. Seiexhibit negative-U properties and show charge states metastability in the D configuration. Mgiacts as only shallow donor (+2/ + 1) in both T and D configurations, in addition we pointed out the role of Mgias electrically activating donor.

Stability and Physicochemical Principles for Icosahedral Ti12X (X = Li to Xe) Clusters: A DFT Study

2008 ◽  
Vol 8 (5) ◽  
pp. 2475-2478
Author(s):  
M. Salazar-Villanueva ◽  
P. H. Hernandez Tejeda ◽  
J. F. Rivas-Silva ◽  
J. A. Ascencio
Keyword(s):  
Density Functional ◽  
Chemical Affinity ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Generalized Gradient Approximation ◽  
Stable Clusters ◽  
The Density Functional Theory ◽  
The Stability ◽  
Chemical Selectivity ◽  
Homo Lumo

Results about stability, electronic structure and characteristic electronic properties are reported for cluster structures based on icosahedra structure with a composition of Ti12X (X = Li to Xe) within the generalized gradient approximation of the density functional theory. It is demonstrated that several elements allow an improvement on the stability of Ti13 by a doping process where the central atoms is substituted. C, Si, P, Co, Ge, Ru and Te lead to the largest gain in energy, while the HOMO-LUMO maximum gap distinguishes to just C, Si, P and Te as the most probable to be found in experimental samples. The analysis included physicochemical study of the most stable clusters to predict chemical affinity and new properties. Results reported here are in agreement with partial studies of Ti12X but because of the considered elements, a new scope is open of possible application mainly in the fields as sensors, catalysis and medicine, where the chemical selectivity is an important parameter.

Structural and elastic properties of ZrN and HfN: ab initio study

2014 ◽  
Vol 92 (9) ◽  
pp. 1058-1061 ◽  
Author(s):  
Anurag Srivastava ◽  
Bhoopendra Dhar Diwan
Keyword(s):  
Elastic Properties ◽  
Density Functional ◽  
Zirconium Nitride ◽  
Energy Calculation ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Hafnium Nitride ◽  
Zinc Blende ◽  
The Density Functional Theory ◽  
The Stability

The present paper discusses the density functional theory based stability analysis of zirconium nitride and hafnium nitride in its rocksalt (B1), CsCl (B2), and zinc blende (B3) type phases. The ground state total energy calculation approach of the system has been used through the generalized gradient approximation parameterized with revised Perdew–Burke–Ernzerhof as exchange correlation functional. The present theoretical analysis confirms the stability trend of phases from most stable to less stable as B1 → B2 → B3. The study also reports the analysis of elastic properties of these nitrides in its most stable B1-type phase.

scholarly journals Effect of Doping Concentration on Structural Stability and Formation Energy of the Fluorine Doped Hexagonal Molybdenum Dioxide (MoO2). A First Principle Study.

2021 ◽  
pp. 55-59
Author(s):  
Yakubu Tanko ◽  
Alhassan Shuaibu ◽  
Aminu Abdulrahman ◽  
Oyedare Olusola ◽  
Mustapha Isa ◽  
...  
Keyword(s):  
Bond Length ◽  
Density Functional ◽  
Formation Energy ◽  
Doping Concentration ◽  
Generalized Gradient ◽  
Molybdenum Dioxide ◽  
Functional Theory ◽  
Free Atoms ◽  
The Stability ◽  
Quantum Espresso

The structural properties of undoped and Fluorine doped Hexagonal Molybdenum dioxide (MoO2) with different doping concentrations have been calculated using Density Functional Theory (DFT) within Generalized Gradient Approximation (GGA) as implemented in Quantum Espresso (QE). The calculated results were for the formation energy of 4.17%, 8.33%, 12.5%, of F doped MoO2 are 232.5eV, 463.0eV, and 698.5eV respectively, which show the variation of energy based on the increase in the doping concentration that led to having the breakage of bond in the structure of the compound. The undoped and 4.17% of F doped MoO2 have three free atoms, which maintain the stability of the structure, but when the doping concentration was increased, the bond breaks simultaneously which led to having four and five free atoms for 8.33%, and 12.5% of F doped MoO2 respectively. This makes 4.17% of F doped MoO2 with 17.09Ry more stable. Similarly, the bond length of undoped MoO2 was 2.2505pm, but when doped with 4.17% of F it changes to 2.3030pm which indicates a greater stability of the structure concentrations of the dopant above 4.17% reduced the bond length, which made the structure less stable.

Novel Silicon–Carbon Fullerene-Like Nanostructures: An Ab Initio Study on the Stability of Si54C6 and Si60C6 Clusters

2006 ◽  
Vol 6 (1) ◽  
pp. 43-53
Author(s):  
Aravind Srinivasan ◽  
Asok K. Ray
Keyword(s):  
Density Functional ◽  
Basis Set ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Silicon Carbon ◽  
Double Zeta ◽  
Valence Electrons ◽  
Symmetry Constraints ◽  
Core Electrons ◽  
The Stability

Silicon fullerene like nanostructures with six carbon atoms on the surface of Si60 cages by substitution, as well as inside the cage at various symmetry orientations have been studied within the generalized gradient approximation to density functional theory. Full geometry optimizations have been performed without any symmetry constraints using the Gaussian 03 suite of programs and the LANL2DZ basis set. Thus, for the silicon atom, the Hay-Wadt pseudopotential with the associated basis set are used for the core electrons and the valence electrons, respectively. For the carbon atom, the Dunning/Huzinaga double zeta basis set is employed. Electronic and geometric properties of the nanostructures are presented and discussed in detail. It was found that optimized silicon–carbon fullerene like nanostructures have increased stability compared to bare Si60 cage and the stability depends on the orientation of carbon atoms, as well as on the nature of bonding between silicon and carbon atoms and also on the carbon–carbon bonding.

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.

Revised prediction of B1 to B2 phase transition pressures in YbN, YbP and YbAs

2005 ◽  
Vol 220 (8) ◽  
Author(s):  
Björn Winkler ◽  
Victor Milman
Keyword(s):  
Phase Transition ◽  
Density Functional Theory ◽  
Density Functional ◽  
Structural Phase ◽  
Quantum Mechanical ◽  
Quantum Mechanical Calculations ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Model Calculations ◽  
B2 Phase

AbstractQuantum mechanical calculations based on density functional theory and a generalized gradient approx imation have been used to study the pressure-induced B1 to B2 structural phase transition in YbN, YbP and YbAs. The phase transitions are predicted to occur at 137 GPa in YbN, at 25 GPa in YbP, and at 20 GPa in YbAs. These values are significantly lower than those predicted by empirical poten tial model calculations. Bulk moduli are predicted to be 136, 70 and 63 GPa for YbN, YbP and YbAs, respectively.

scholarly journals Structural, electronic, and elastic properties of Tetragonal Sr0.5Be0.5TiO3: Ab-initio calculation.

2021 ◽  
Vol 67 (2 Mar-Apr) ◽  
pp. 299
Author(s):  
M. Tedjani
Keyword(s):  
Elastic Properties ◽  
Density Functional ◽  
Local Density ◽  
Partial Density ◽  
Full Potential ◽  
Generalized Gradient ◽  
Functional Theory ◽  
The Stability ◽  
First Time ◽  
Linearized Augmented Plane Wave

In this theoretical study, we presents  for the first time, to the best of our knowledge, the structural, electronic and elastic properties of perovskite Sr0.5Be0.5TiO3 type structure (Tetragonal), P4/mmm, space group, 123.using full potential linearized augmented plane wave (FP-LAPW) method on the basis of density functional theory (DFT) integrated in the Wien2k code . The generalized gradient approximation (GGA-PBEsol) and local density approximation has been used for the exchange correlation potential .The electronic properties represented by the band structure (BS) and DOS as well as the (PDOS) partial density of states, allowed to obtain  semiconductor compound, which have been calculated with mBJ approximation. The elastic constants were reported and we verified the stability conditions of our materials elastically. These theoretical results open the way for experimental and other theoretical studies of this compound.

scholarly journals First-Principle Study of Zinc Sulfide (Zinc Blende, Rock Salt and Wurtzite): Stability, Phase Transition and Structural Parameters

2020 ◽  
pp. 313-318
Author(s):  
Ibrahim Isah ◽  
Mustapha Isah
Keyword(s):  
Phase Transition ◽  
Zinc Sulfide ◽  
Rock Salt ◽  
Density Functional ◽  
Structural Parameters ◽  
First Principle ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Zinc Blende ◽  
The Stability

The research investigates the stability, phase transition and structural parameters of zinc sulfide (Zinc blende, Rock salt and Wurtzite) using first-principle. The study employs generalized gradient approximation (GGA) within density functional theory (DFT) in which ultra-soft pseudopotential (Zn.pbe-van.UPFb and S.pbe-van_bm.UPFc ) were used for both zinc and sulfide respectively. Self-consistent calculation was made using cut-off energies of 26Ry (~350 eV) and 180 Ry (~2450eV) for the cut-off wave function within the convergence accuracy of ~1mRy with respect to total energy and 0.5kbar in case of pressure. The results obtained show that Wurtzite is more stable because it has lowest energy among the three structures, there is transition from zinc blende to rock salt and from Wurtzite to rock salt with transition pressures of 17.5GPa and 16.9GPa respectively and all the three polymorphs are semi-conductors due to their band gap.

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