scholarly journals An Investigation on Substitution of Ag Atoms for Al or Ti Atoms in the Ti2AlC MAX Phase Ceramic Based on First-Principles Calculations

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7068
Author(s):  
Guochao Wang ◽  
Jiahe Zhou ◽  
Weijian Chen ◽  
Jianguo Yang ◽  
Jie Zhang ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Fermi Level ◽  
First Principles ◽  
First Principles Calculation ◽  
Max Phase ◽  
Lattice Stability ◽  
Substitution Ratio ◽  
New Perspective ◽  
The Stability ◽  
Bonding Characteristic

The present work introduced first-principles calculation to explore the substitution behavior of Ag atoms for Al or Ti atoms in the Ti2AlC MAX phase ceramic. The effect of Ag substitution on supercell parameter, bonding characteristic, and stability of the Ti2AlC was investigated. The results show that for the substitution of Ag for Al, the Al-Ti bond was replaced by a weaker Ti-Ag bond, decreasing the stability of the Ti2AlC. However, the electrical conductivity of the Ti2AlC was enhanced after the substitution because of the contribution of Ag 4d orbital electrons toward the density of states (DOS) at the Fermi level coupled with the filling of Ti d orbital electrons. For the substitution of Ag for Ti, new bonds, such as Ag-Al bond, Ag-C bond, Al-Al bond, Ti-Ti anti-bond, and C-C anti-bond were generated in the Ti2AlC. The Ti-Ti anti-bond was strengthened as well as the number of C-C anti-bond was increased with increasing the substitution ratio of Ag for Ti. Similar to the substitution of Ag for Al, the stability of the Ti2AlC also decreased because the original Al-Ti bond became weaker as well as the Ti-Ti and C-C anti-bonds were generated during the substitution of Ag for Ti. Comparing with the loss of Ti d orbital electrons, Ag 4d orbits contributed more electrons to the DOS at the Fermi level, improving the electrical conductivity of the Ti2AlC after substitution. Based on the calculation, the substitution limit of Ag for Al or Ti was determined. At last, the substitution behavior of Ag for Al or Ti was compared to discriminate that Ag atoms would tend to preferentially substitute for Ti atoms in Ti2AlC. The current work provides a new perspective to understand intrinsic structural characteristic and lattice stability of the Ti2AlC MAX phase ceramic.

scholarly journals New MAX Phase Superconductor Ti2GeC: A First-principles Study

2013 ◽  
Vol 6 (1) ◽  
pp. 11-27 ◽  
Author(s):  
M. A. Hadi ◽  
M. Roknuzzaman ◽  
F. Parvin ◽  
S. H. Naqib ◽  
A. K. M. A. Islam ◽  
...  
Keyword(s):  
Optical Properties ◽  
Thermodynamic Properties ◽  
Fermi Surface ◽  
Vickers Hardness ◽  
First Principles ◽  
Elastic Anisotropy ◽  
Debye Model ◽  
First Principles Calculation ◽  
Max Phase ◽  
Specific Heats

This is the first DFT-based first-principles prediction of the detailed optical and thermodynamic properties, including Vickers hardness and Fermi surface of 211 MAX phase Ti2GeC for which superconductivity (Tc~ 9.5 K) was reported very recently. The calculated structural properties are in excellent agreement with experiments. Our results on elastic parameters indicate a slight elastic anisotropy and brittleness of the compound. The chemical bonding is seen to be a combination of covalent, ionic and metallic nature. The rather stronger covalent bonding is responsible for its high Vickers hardness of 11.6 GPa. The investigated Fermi surface is formed mainly by the low-dispersive bands, which should be responsible for the presence of superconductivity in Ti2GeC. All the optical properties are evaluated and analyzed for two different polarization directions of incident photon. The temperature and pressure dependence of primitive cell volume, thermal expansion coefficient, specific heats, bulk modulus, and Debye temperature of Ti2GeC are derived from the quasi-harmonic Debye model with phononic effect and the various implications are discussed in details.  Keywords: First-principles calculation; Vickers hardness; Optical properties; Thermodynamic properties. © 2014 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. doi: http://dx.doi.org/10.3329/jsr.v6i1.16604 J. Sci. Res. 6 (1), 11-27 (2014)

scholarly journals Theory of Hydrogen Reactions in Silicon

1987 ◽  
Vol 104 ◽  
Author(s):  
Chris G. Van De Walle ◽  
Y. Bar-Yam ◽  
S. T. Pantelides
Keyword(s):  
Fermi Level ◽  
Total Energy ◽  
First Principles ◽  
Type Material ◽  
Energy Calculations ◽  
And Migration ◽  
The Stability ◽  
Hydrogen Reactions ◽  
Energy Surfaces ◽  
P Type

ABSTRACTWe report first-principles total-energy calculations for H atoms in a Si lattice. Our results for single H atoms are presented in the form of total-energy surfaces, providing immediate insight in stable positions and migration paths. We examine the stability of different charge states (H+, H0, H−) as a function of Fermi-level position, and its impli-cations for H diffusion in p-type vs. n-type material. The results are used to scrutinize and supplement existing understanding of experimental observations. We also study the co-operative interactions of several H atoms, and propose a novel mechanism for H-induced damage.

Stability and Reactivity of [11-20] Step in Initial Stage of Epitaxial Graphene Growth on SiC(0001)

2014 ◽  
Vol 778-780 ◽  
pp. 1150-1153
Author(s):  
Hiroyuki Kageshima ◽  
Hiroki Hibino ◽  
Hiroshi Yamaguchi ◽  
Masao Nagase
Keyword(s):  
Surface Morphology ◽  
First Principles ◽  
Epitaxial Graphene ◽  
First Principles Calculation ◽  
Control Parameters ◽  
Graphene Growth ◽  
Initial Stage ◽  
The Stability

The energetics for the Si desorption and the C adsorption at a [11-20] step on SiC(0001) surface are studied using the first-principles calculation. It is found that the [11-20] step is stable and nonreactive. The stability of the step is thought to govern the surface morphology during the graphene formation. It is shown that the Si pressure and the temperature are the control parameters for the surface morphology and the graphene quality.

scholarly journals Effects of Doped Elements (Si, Cr, W and Nb) on the Stability, Mechanical Properties and Electronic Structures of MoAlB Phase by the First-Principles Calculation

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4221
Author(s):  
Yongxin Jian ◽  
Zhifu Huang ◽  
Yu Wang ◽  
Jiandong Xing
Keyword(s):  
Mechanical Properties ◽  
Chemical Bonding ◽  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
Formation Enthalpy ◽  
First Principles Calculation ◽  
Elemental Doping ◽  
The Stability ◽  
W Doping

First-principles calculations based on density functional theory (DFT) have been performed to explore the effects of Si, Cr, W, and Nb elements on the stability, mechanical properties, and electronic structures of MoAlB ternary boride. The five crystals, with the formulas of Mo4Al4B4, Mo4Al3SiB4, Mo3CrAl4B4, Mo3WAl4B4, and Mo3NbAl4B4, have been respectively established. All the calculated crystals are thermodynamically stable, according to the negative cohesive energy and formation enthalpy. By the calculation of elastic constants, the mechanical moduli and ductility evolutions of MoAlB with elemental doping can be further estimated, with the aid of B/G and Poisson’s ratios. Si and W doping cannot only enhance the Young’s modulus of MoAlB, but also improve the ductility to some degree. Simultaneously, the elastic moduli of MoAlB are supposed to become more isotropic after Si and W addition. However, Cr and Nb doping plays a negative role in ameliorating the mechanical properties. Through the analysis of electronic structures and chemical bonding, the evolutions of chemical bondings can be disclosed with the addition of dopant. The enhancement of B-B, Al/Si-B, and Al/Si-Mo bondings takes place after Si substitution, and W addition apparently intensifies the bonding with B and Al. In this case, the strengthening of chemical bonding after Si and W doping exactly accounts for the improvement of mechanical properties of MoAlB. Additionally, Si doping can also improve the Debye temperature and melting point of the MoAlB crystal. Overall, Si element is predicted to be the optimized dopant to ameliorate the mechanical properties of MoAlB.

First-principles study of Cu adsorption on vacancy-defected/Au-doped graphene

2018 ◽  
Vol 32 (11) ◽  
pp. 1850139 ◽  
Author(s):  
Yang Liu ◽  
Libao An ◽  
Liang Gong
Keyword(s):  
First Principles ◽  
Population Analysis ◽  
First Principles Calculation ◽  
Matrix Composites ◽  
Mulliken Population ◽  
Vacancy Defects ◽  
Subsequent Investigation ◽  
Doped Graphene ◽  
The Stability ◽  
P Type

To enhance the interaction between Cu and graphene in graphene reinforced Cu matrix composites, the first principles calculation was carried out to study the adsorption of Cu atoms on graphene. P-type doping and n-type doping were formed, respectively, on vacancy-defected and Au-doped graphene based on band structure analysis, and this was verified by subsequent investigation on density of states. A computation on charge transfer confirmed that p-type doping could promote the electron transport between Cu and graphene, while n-type doping would prevent it. In addition, adsorption energy and Mulliken population analysis revealed that both vacancy defects and Au doping could improve the stability of the Cu–graphene system. The research conducted in this paper provides useful guidance for the preparation of Cu/graphene composites.

STRUCTURAL AND ELECTRONIC EVOLUTION FROM SiC SHEET TO SILICENE

2013 ◽  
Vol 27 (32) ◽  
pp. 1350188 ◽  
Author(s):  
G. LIU ◽  
M. S. WU ◽  
C. Y. OUYANG ◽  
B. XU
Keyword(s):  
Density Functional Theory ◽  
Fermi Level ◽  
Density Of States ◽  
First Principles ◽  
Density Functional ◽  
Band Gaps ◽  
Functional Theory ◽  
Orbital Contribution ◽  
Structural And Electronic Properties ◽  
Substitution Ratio

The evolution of the structural and electronic properties from SiC sheet to silicene is studied by using first-principles density functional theory. It is found that the planar configurations of the Si – C monolayer systems are basically kept except for the increase of the buckling of the planar structure when the substitution ratio of Si increases. Band gaps of the Si – C monolayer system decrease gradually when the substitution ratio of Si atoms ranges from 0% to 100%. The energy and type of the band gaps are closely related with the substitution ratio of Si atoms and the Si – C order. Further analysis of density of states reveals the orbital contribution of Si and C atoms near the Fermi level. The discussion of the electronic evolution from SiC sheet to silicene would widen the application of the Si – C monolayer systems in the optoelectronic field in the future nanotechnology.

scholarly journals Half-Metallicity and Magnetism of the Quaternary Heusler Compound TiZrCoIn1−xGex from the First-Principles Calculations

2019 ◽  
Vol 9 (4) ◽  
pp. 620 ◽  
Author(s):  
Ying Chen ◽  
Shaobo Chen ◽  
Bin Wang ◽  
Bo Wu ◽  
Haishen Huang ◽  
...  
Keyword(s):  
Fermi Level ◽  
First Principles ◽  
Magnetic Moments ◽  
First Principles Calculations ◽  
Half Metallicity ◽  
Valence Electrons ◽  
The Stability ◽  
Formation Energies ◽  
Quaternary Heusler Compound ◽  
Ge Doping

The effects of doping on the electronic and magnetic properties of the quaternary Heusler alloy TiZrCoIn were investigated by first-principles calculations. Results showed that the appearance of half-metallicity and negative formation energies are associated in all of the TiZrCoIn1−xGex compounds, indicating that Ge doping at Z-site increases the stability without damaging the half-metallicity of the compounds. Formation energy gradually decreased with doping concentration, and the width of the spin-down gap increased with a change in Fermi level. TiZrCoIn0.25Ge0.75 was found to be the most stable half-metal. Its Fermi level was in the middle of the broadened gap, and a peak at the Fermi level was detected in the spin majority channel of the compound. The large gaps of the compounds were primarily dominated by the intense d-d hybridization between Ti, Zr, and Co. The substitution of In by Ge increased the number of sp valence electrons in the system and thereby enhanced RKKY exchange interaction and increased splitting. Moreover, the total spin magnetic moments of the doped compounds followed the Slater–Pauling rule of Mt = Zt − 18 and increased from 2 μB to 3 μB linearly with concentration.

First-Principles Study of 3D Transition Metal Doped Single-Layer Graphene

2020 ◽  
Vol 984 ◽  
pp. 82-87
Author(s):  
Bao Zhu Wang ◽  
Sheng Tang ◽  
Tong Wei ◽  
Jie Ren ◽  
Min Wang
Keyword(s):  
Fermi Level ◽  
First Principles ◽  
Density Functional ◽  
Single Layer ◽  
First Principles Calculation ◽  
Single Layer Graphene ◽  
Impurity Level ◽  
Layer System ◽  
Magnetic Ground State ◽  
Metal Doped

The electronic structure and magnetic properties of C atoms in Co, Ni-substituted graphene single-layers were studied by first-principles calculation method based on density functional theory. The study found that the pure graphene single-layer is an insulator, does not have magnetism, and we found that the doping of Co and Ni atoms alone does not make the system magnetic. Both Co and Ni atoms are capable of generating impurity levels in the graphene single-layer system. The impurity level of Co atom doping is 0.75 eV below the Fermi level, and the impurity level of Ni atom doping is 0.4 eV above the Fermi level. Studies on the coupling doping of Co and Ni atoms show that two different distance Co atoms or Ni atoms in the graphene single-layer are not always ferromagnetically coupled, and a stable magnetic ground state cannot be obtained. It can produce different magnetic ground states by controlling different doping distances, thus we provide one new way to control the spin properties.

First-principles study on the electronic and magnetic properties of the Zn0.75Mo0.25M(M = S,Se,Te)

2016 ◽  
Vol 30 (19) ◽  
pp. 1650249 ◽  
Author(s):  
Zhu-Hua Yin ◽  
Jian-Min Zhang ◽  
Ke-Wei Xu
Keyword(s):  
Magnetic Properties ◽  
Fermi Level ◽  
First Principles ◽  
Atomic Radius ◽  
Band Gaps ◽  
First Principles Calculation ◽  
Spintronic Devices ◽  
Lattice Constants ◽  
Electronic And Magnetic Properties ◽  
Tetrahedral Crystal

The geometrical, electronic and magnetic properties of the Zn[Formula: see text]Mo[Formula: see text]M (M[Formula: see text]=[Formula: see text]S, Se and Te) have been studied by spin-polarized first-principles calculation. The optimized lattice constants of 5.535, 5.836 and 6.274 Å for M[Formula: see text]=[Formula: see text]S, Se and Te are related to the atomic radius of 1.09, 1.22 and 1.42 Å for S, Se and Te atoms, respectively. The Zn[Formula: see text]Mo[Formula: see text]M are magnetic half-metallic (HM) with the spin-down conventional band gaps of 2.899, 2.126 and 1.840 eV, while the HM band gaps of 0.393, 0.016 and 0.294 eV for M[Formula: see text]=[Formula: see text]S, Se and Te, respectively. At the Fermi level, the less than half-filled Mo-[Formula: see text] orbital hybridizated with the less M-[Formula: see text] orbital contributes only spin-up channel leading Zn[Formula: see text]Mo[Formula: see text]M an HM ferromagnetism. The tetrahedral crystal field formed by adjacent three Zn atoms and one M atom splits the spin-up channel (majority spin) of Mo-[Formula: see text] orbital into three-fold degenerate [Formula: see text] states at the Fermi level and double degenerate [Formula: see text] [Formula: see text] states below the Fermi level. The exchange splitting energies of the Zn[Formula: see text]Mo[Formula: see text]M are −2.611, −2.231 and −1.717 eV for M[Formula: see text]=[Formula: see text]S, Se and Te, respectively. The results provide an useful theoretical guidance for Zn[Formula: see text]Mo[Formula: see text]M applications in spintronic devices.

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