Stabilizing Effect of (100) Compound Twinning in NiTi Martensite

Stabilizing Effect ◽

Full Optimization ◽

Experimental Findings ◽

Martensite Structure ◽

According to experimental findings, the martensite structure of NiTi is monoclinic (B19'). However, previous first principles calculations have shown that, after a full optimization of the lattice, the ideal martensite structure relaxed into orthorhombic B33 structure. Present calculations reveal that a presence of twins in a real martensite can stabilize the B19' structure.

On the Possibility of Passivation of Si(100) by Adsorption of Group-VI Atoms

MRS Proceedings ◽

10.1557/proc-193-143 ◽

1990 ◽

Vol 193 ◽

Author(s):

Efthimios Kaxiras

Keyword(s):

First Principles ◽

Relative Strength ◽

Energy Costs ◽

Qualitative Information ◽

Group Vi ◽

Covalent Bonds ◽

Large Dispersion ◽

Monolayer Coverage ◽

ABSTRACTThe possibility of passivating the Si(100) surface by adsorption of Group-VI atoms (S and Se) is investigated through first-principles calculations. The structure of the ideal (1×1) configuration with the Si surface dangling bonds saturated by full monolayer coverage is examined in detail. The Group-VI adsorbates form covalent bonds to the substrate with bond-lengths very close to the sums of the covalent radii. The bond-angles are larger than in bulk configurations of the Group-VI elements. The ideal (1×1) configuration gives rise to a surface electronic state with large dispersion spanning the entire band-gap of Si. Deviations from this configuration by in-phase or out-of-phase tilting of the adsorbate atoms result in energy costs which can give qualitative information on the relative strength of adsorbate-adsorbate and adsorbate-substrate interactions.

A comparison of the ideal strength between L12Co3(Al,W) and Ni3Al under tension and shear from first-principles calculations

Applied Physics Letters ◽

10.1063/1.3170752 ◽

2009 ◽

Vol 94 (26) ◽

pp. 261909 ◽

Cited By ~ 54

Author(s):

Yun-Jiang Wang ◽

Chong-Yu Wang

Keyword(s):

First Principles ◽

Ideal Strength ◽

Systematic first principles calculations of the effects of stacking faults defects on the 4H-SiC band structure

MRS Proceedings ◽

10.1557/proc-1246-b03-07 ◽

2010 ◽

Vol 1246 ◽

Cited By ~ 1

Author(s):

Massimo Camarda ◽

pietro delugas ◽

Andrea Canino ◽

Andrea Severino ◽

nicolo piluso ◽

...

Keyword(s):

First Principles ◽

Density Functional ◽

Stacking Faults ◽

Perfect Crystal ◽

Electronic Band ◽

Functional Theory ◽

Experimental Findings ◽

Electronic Band Structures ◽

Formation Energies

AbstractShockley-type Stacking faults (SSF) in hexagonal Silicon Carbide polytypes have received considerable attention in recent years since it has been found that these defects are responsible for the degradation of forward I-V characteristics in p-i-n diodes. In order to extend the knowledge on these kind of defects and theoretically support experimental findings (specifically, photoluminescence spectral analysis), we have determined the Kohn-Sham electronic band structures, along the closed path Γ-M-K-Γ, using density functional theory. We have also determined the energies of the SSFs with respect to the perfect crystal finding that the (35) and (44) SSFs have unexpectedly low formation energies, for this reason we could expect these two defects to be easily generated/expanded either during the growth or post-growth process steps.

First-Principles Calculations of Grain Boundary-Surface for Various Grain Boundaries with Different Energies in Aluminum

Materials Science Forum ◽

10.4028/www.scientific.net/msf.551-552.331 ◽

2007 ◽

Vol 551-552 ◽

pp. 331-336 ◽

Cited By ~ 2

Author(s):

Tokuteru Uesugi ◽

Y. Inoue ◽

Yorinobu Takigawa ◽

Kenji Higashi

Keyword(s):

Shear Strength ◽

Grain Boundary ◽

First Principles ◽

Boundary Surface ◽

Grain Boundary Sliding ◽

Excess Energy ◽

Perfect Single Crystal ◽

Boundary Sliding ◽

The grain boundary surface is the excess energy of the grain boundary as the lattice on one side of the grain is translated relative to the lattice on the other side of the grain. The maximum in the slope of the grain boundary surface determines the ideal shear strength for the grain boundary sliding. We presented the ideal shear strength for the grain boundary sliding in aluminum Σ3(11 2)[110] tilt grain boundary from the first-principles calculations. The ideal shear strength for the grain boundary sliding was much smaller than the ideal shear strength of a perfect single crystal.

Probing embedded topological modes in bulk-like GeTe-Sb2Te3 heterostructures

Scientific Reports ◽

10.1038/s41598-020-76885-7 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Hisao Nakamura ◽

Johannes Hofmann ◽

Nobuki Inoue ◽

Sebastian Koelling ◽

Paul M. Koenraad ◽

...

Keyword(s):

Topological Insulator ◽

First Principles ◽

Atom Probe ◽

Photoemission Spectroscopy ◽

Band Offset ◽

Vacuum Interface ◽

Topological States ◽

Experimental Findings ◽

Thick Layers

AbstractThe interface between topological and normal insulators hosts metallic states that appear due to the change in band topology. While topological states at a surface, i.e., a topological insulator-air/vacuum interface, have been studied intensely, topological states at a solid-solid interface have been less explored. Here we combine experiment and theory to study such embedded topological states (ETSs) in heterostructures of GeTe (normal insulator) and $$\hbox {Sb}_2$$ Sb 2 $$\hbox {Te}_3$$ Te 3 (topological insulator). We analyse their dependence on the interface and their confinement characteristics. First, to characterise the heterostructures, we evaluate the GeTe-Sb$$_2$$ 2 Te$$_3$$ 3 band offset using X-ray photoemission spectroscopy, and chart the elemental composition using atom probe tomography. We then use first-principles to independently calculate the band offset and also parametrise the band structure within a four-band continuum model. Our analysis reveals, strikingly, that under realistic conditions, the interfacial topological modes are delocalised over many lattice spacings. In addition, the first-principles calculations indicate that the ETSs are relatively robust to disorder and this may have practical ramifications. Our study provides insights into how to manipulate topological modes in heterostructures and also provides a basis for recent experimental findings [Nguyen et al. Sci. Rep. 6, 27716 (2016)] where ETSs were seen to couple over thick layers.

The Clustering of Zn6Y9 and its Predominant Role in Long Period Stacking Order Phases in Mg-Zn-Y Alloys: A First-Principles Study

Materials Science Forum ◽

10.4028/www.scientific.net/msf.749.569 ◽

2013 ◽

Vol 749 ◽

pp. 569-576 ◽

Cited By ~ 3

Author(s):

Shang Yi Ma ◽

Li Min Liu ◽

Shao Qing Wang

Keyword(s):

First Principles ◽

Building Block ◽

Stacking Fault ◽

Predominant Role ◽

Lpso Phase ◽

Local Structures ◽

Long Period ◽

Stacking Order ◽

The local structures of Zn and Y in the long period stacking order (LPSO) phase in Mg-Zn-Y system were investigated by first principles calculations in details. The clustering of Zn and Y atoms ranging from single stacking fault layer to four consecutive layers was explicitly demonstrated. The calculations indicate that Zn and Y atoms prefer clustering in the form of Zn6Y9 embedding in ABCA-type building block to the random or ordered arrangements of Zn and Y atoms being enriched in two stacking fault layers. The cluster of Zn6Y9 can be regarded as the ideal stoichiometric component of LPSO and it plays a predominant role in the LPSO phases. The formation of LPSO phases is highly associated with the Zn6Y9 cluster and its derivatives.

Characterizing modulated structures with first-principles calculations: a unified superspace scheme of ordering in mullite

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273319000846 ◽

2019 ◽

Vol 75 (2) ◽

pp. 260-272 ◽

Cited By ~ 1

Author(s):

Paul Benjamin Klar ◽

Iñigo Etxebarria ◽

Gotzon Madariaga

Keyword(s):

Phase Diagram ◽

Density Functional Theory ◽

First Principles ◽

Density Functional ◽

Complex Nature ◽

Functional Theory ◽

Modulated Structures ◽

Total Energies ◽

The benefit of computational methods applying density functional theory for the description and understanding of modulated crystal structures is investigated. A method is presented which allows one to establish, improve and test superspace models including displacive and occupational modulation functions from first-principles calculations on commensurate structures. The total energies of different configurations allow one to distinguish stable and less stable structure models. The study is based on a series of geometrically optimized superstructures of mullite (Al4+2x Si2−2x O10−x ) derived from the superspace group Pbam(α0½)0ss. Despite the disordered and structurally complex nature of mullite, the calculations on ordered superstructures are very useful for determining the ideal Al/Si ordering in mullite, extracting atomic modulation functions as well as understanding the SiO2–Al2O3 phase diagram. The results are compared with experimentally established models which confirm the validity and utility of the presented method.

Ultimate Mechanical Properties of Forsterite

Minerals ◽

10.3390/min9120787 ◽

2019 ◽

Vol 9 (12) ◽

pp. 787 ◽

Cited By ~ 2

Author(s):

Karine Gouriet ◽

Philippe Carrez ◽

Patrick Cordier

Keyword(s):

Mechanical Properties ◽

First Principles ◽

Shear Plane ◽

Shear Loading ◽

High Symmetry ◽

Generalized Gradient ◽

Generalized Gradient Approximation ◽

Homogeneous Strain ◽

The ultimate mechanical properties, as characterized here by the ideal strengths of Mg2SiO4 forsterite, have been calculated using first-principles calculations and generalized gradient approximation under tensile and shear loading. The ideal tensile strengths (ITS) and ideal shear strengths (ISS) are computed by applying homogeneous strain increments along high-symmetry directions ([100], [010], and [001]) and low index shear plane ((100), (010), and (001)) of the orthorhombic lattice. We show that the ultimate mechanical properties of forsterite are highly anisotropic, with ITS ranging from 12.1 GPa along [010] to 29.3 GPa along [100], and ISS ranging from 5.6 GPa for simple shear deformation along (100) to 11.5 GPa for shear along (010).

Mechanical Properties and Stability of Body-Centered-Tetragonal C8 at High Pressures

Zeitschrift für Naturforschung A ◽

10.1515/zna-2018-0164 ◽

2018 ◽

Vol 73 (10) ◽

pp. 939-945

Author(s):

Chenyang Zhao ◽

Qun Wei ◽

Haiyan Yan ◽

Bing Wei

Keyword(s):

Mechanical Properties ◽

First Principles ◽

Pressure Range ◽

Superhard Material ◽

High Pressures ◽

Elastic Anisotropy ◽

Acoustic Velocity ◽

Large Strains ◽

AbstractThe structural, mechanical, electronic properties and stability of body-centered-tetragonal C8 (Bct-C8) were determined by using the first-principles calculations. Bct-C8 is identified to be mechanically and dynamically stable at a pressure range from 0 to 100 GPa. The elastic anisotropy, average acoustic velocity and Debye temperature of Bct-C8 at ambient and high pressures were studied. The ideal stresses at large strains of Bct-C8 were examined; the results showed that it would cleave under the tensile strength of 72 GPa or under the shear strength of 70 GPa, indicating that Bct-C8 is a potential superhard material.