There has been considerable recent interest in the design of diluted magnetic semiconductors, with a particular focus on exploration different semiconductor hosts. Among these, oxide-based semiconductors are attracting increasing attention, following reports room temperature ferromagnetism anatase TiO2 and wurtzite ZnO doped range transition metal ions. In this review we summarize current status discuss influence growth method, substrate choice, microstructure subsequent properties thin...

We present a first-principles computational study of the nature and origin ferromagnetism in Co-doped $\mathrm{Ti}{\mathrm{O}}_{2}$. calculate magnetic ordering electronic properties as function concentration distribution Co dopants oxygen vacancies. find that atoms prefer to substitute on neighboring sites Ti lattice, show, using well-established Goodenough-Kanamori-Anderson rules, this leads ferromagnetic superexchange. propose other semiconductor hosts which superexchange mechanism should...

The internal twin-boundaries in lamellar γ-TiAl alloys, namely true-twin (TT), rotational boundary (RB), and pseudo-twin (PT), are known to be effective strengthening the TiAl microstructures. Nevertheless, for designing microstructures with optimised mechanical properties, a better understanding of role these boundaries on fracture behavior is still required. To this end, we study how what degree crack advancement affected by local lattice orientation atomic structure at various twin...

Strengthening of metals by incorporating nano-scale coherent twin boundaries is one the important breakthroughs recent years in overcoming strength-ductility trade-off. To this effect, also nano-lamellar lightweight Ti-Al alloys promise a great potential, but their contribution to deformation and fracture behavior needs be better understood for designing optimal microstructures. end, we carry out linear elastic mechanics informed large-scale atomistic simulations fully lamellar...

We have performed ab-initio tensile tests of bulk Al along different axes, as well perpendicular to grain boundaries determine mechanical properties such interface energy, work separation and theoretical strength. show that all the investigated geometries exhibit energy-displacement curves can be brought into coincidence in spirit known universal binding energy relationship curve. This simplifies significantly calculation strengths for whole parameter space boundaries.

We have determined the influence of carbon on mechanical properties such as grain boundary energy, work separation (WoS) and fracture strength Σ5(3 1 0)[0 0 1] symmetrical tilt (STGB) in molybdenum with ab initio methods. From our results, we derived traction–separation laws that can be used continuum simulations employing cohesive zones. Our results show an increasing number C atoms at boundary, energy is lowered, indicating a strong driving force for segregation. Uni-axial tensile tests...

The influence of the interstitial impurities B, C, N, O, and H on interfacial cohesion structure grain boundaries in body-centered cubic transition metals is investigated by means local-density-functional theory (LDFT), using mixed-basis pseudopotential approach. $\ensuremath{\Sigma}5$ (310) [001] symmetrical tilt (STGB) Nb Mo are chosen for this theoretical case study. analysis interface energies geometric translation states, site-projected densities states bonding electron yields following...

The migration of grain boundaries leads to growth in polycrystals and is one mechanism grain-boundary-mediated plasticity, especially nanocrystalline metals. This due the movement dislocationlike defects, called disconnections, which couple externally applied shear stresses. While this has been studied detail recent years, active disconnection mode was typically associated with specific macroscopic boundary parameters. We know, however, that varying microscopic degrees freedom can lead...

For the first time, doping efficiency and defect evolution of p-type by aluminum in SiC are clarified distinguished an MD study.

Abstract

Hydrogen embrittlement, which severely affects structural materials such as steel, comprises several mechanisms at the atomic level. One of them is hydrogen enhanced decohesion (HEDE), phenomenon H accumulation between cleavage planes, where it reduces interplanar cohesion. Grain boundaries are expected to play a significant role for HEDE, since they act trapping sites hydrogen. To elucidate this mechanism, we present results first-principles studies effect on cohesive strength α-Fe single...

Using in-situ nanoindentation experiments it is possible to study the dislocation mechanisms which unfold under an indenter.Large-scale atomistic simulations of same are due similarities in length scale, provided that defects can be included simulation. Yet, have so far been mostly undertaken on defect free samples, while studies with pre-existing few. The latter show average hardness not affected by presence defects, justifies use ideal crystals such simulations. However, this observation...

γ/γ interfaces drive plastic deformation in lamellar TiAl alloys. Due to the ordering and resulting tetragonal nature of γ phase, twin exist as different variants, some which exhibit coherency stresses or semicoherent interface structures. While geometric parameters, such lamella spacing orientation, are explored extensively experiments, isolation individual influence a nanolamellar microstructure remains challenge. Herein, range states is modeled using bilayers coherent TrueTwin ,...

Abstract Semi-coherent interfaces can have a strong influence on the mechanical behavior of bilayer systems, which is seen very clearly under indentation conditions where well-defined plastic zone interacts directly with interface. The main aim this work to study semi-coherent bcc/bcc interface in V/Fe system molecular dynamics (MD) simulations. In particular, V layer thicknesses apparent hardness investigated. Our results show that deformation pure and Fe resulting from MD simulations good...

Hydrogen enhanced decohesion is expected to play a major role in ferritic steels, especially at grain boundaries. Here, we address the effects of some common alloying elements C, V, Cr, and Mn on H segregation behaviour mechanism Σ 5 ( 310 ) [ 001 ] 36.9 ∘ boundary bcc Fe using spin polarized density functional theory calculations. We find that enhance cohesion. Furthermore, all have an influence energies interstitial as well these elements’ impact V slightly promotes cohesion enhancing...

Abstract Whether a metallic material fractures by brittle cleavage or ductile rupture is primarily governed the competition between and dislocation emission at crack tip. The linear elastic fracture mechanics (LEFM) based criterion of Griffith, respectively one for Rice, are sufficiently reliable determining possible tip propagation mechanisms in isotropic crystalline metals. However, applicability these criteria questionable when non-cubic, anisotropic solids considered, as e.g. ordered...

Atomic-scale stages of the growth an interfacial precipitate film tetragonal molybdenum carbide at a $\ensuremath{\Sigma}5$ (310) [001] symmetrical tilt grain boundary in body-centered cubic were investigated by means atomistic supercell calculations on basis ab initio density functional theory. The structural development with increasing carbon concentration is analyzed qualitatively and quantitatively. structurally optimized model for fully developed compared to experimental high-resolution...