78 research outputs found
Exploring N-rich phases in LixNy clusters for hydrogen storage at nano-scale
We have performed cascade genetic algorithm and ab initio atomistic
thermodynamics under the framework of first-principles density functional
theory to study the (meta-)stability of a wide range of LixNy clusters. We
found that hybrid xc-functional is essential to address this problem as a
local/semi-local functional simply fails even to predict a qualitative
prediction. Most importantly, we find that though in bulk Lithium Nitride, Li
rich phase, i.e. Li3N, is the stable stoichiometry, in small LixNy clusters
N-rich phases are more stable at thermodynamic equilibrium. We further show a
that these N-rich clusters are promising hydrogen storage material because of
their easy adsorption and desorption ability at respectively low (< 300K) and
moderately high temperature (> 600K).Comment: 5 pages, 4 figure
A phase-field study of elastic stress effects on phase separation in ternary alloys
Most of the commercially important alloys are multicomponent, producing
multiphase microstructures as a result of processing. When the coexisting
phases are elastically coherent, the elastic interactions between these phases
play a major role in the development of microstructures. To elucidate the key
effects of elastic stress on microstructural evolution when more than two
misfitting phases are present in the microstructure, we have developed a
microelastic phase-field model in two dimensions to study phase separation in
ternary alloy system. Numerical solutions of a set of coupled Cahn-Hilliard
equations for the composition fields govern the spatiotemporal evolution of the
three-phase microstructure. The model incorporates coherency strain
interactions between the phases using Khachaturyan's microelasticity theory. We
systematically vary the misfit strains (magnitude and sign) between the phases
along with the bulk alloy composition to study their effects on the
morphological development of the phases and the resulting phase separation
kinetics. We also vary the ratio of interfacial energies between the phases to
understand the interplay between elastic and interfacial energies on
morphological evolution. The sign and degree of misfit affect strain
partitioning between the phases during spinodal decomposition, thereby
affecting their compositional history and morphology. Moreover, strain
partitioning affects solute partitioning and alters the kinetics of coarsening
of the phases. The phases associated with higher misfit strain appear coarser
and exhibit wider size distribution compared to those having lower misfit. When
the interfacial energies satisfy complete wetting condition, phase separation
leads to development of stable core-shell morphology depending on the misfit
between the core (wetted) and the shell (wetting) phases
Multiple Zeeman-type Hidden Spin Splitting in -Symmetric Layered Antiferromagnets
Centrosymmetric antiferromagnetic semiconductors, although abundant in
nature, appear less favorable in spintronics owing to the lack of inherent spin
polarization and magnetization. We unveil hidden Zeeman-type spin splitting
(HZSS) in layered centrosymmetric antiferromagnets with asymmetric sublayer
structures by employing first-principles simulations and symmetry analysis.
Taking the bilayer counterpart of recently synthesized monolayer MnSe, we
demonstrate that the degenerate states around specific high-symmetry points
spatially segregate on different sublayers forming PT-symmetric pair.
Furthermore, degenerate states exhibit uniform in-plane spin configurations
with opposite orientations enforced by mirror symmetry. Bands are locally
Zeeman-split up to order of 70 meV. Strikingly, a tiny electric field of a few
mVA-1 along the z-direction breaks the double degeneracy forming additional
Zeeman pair. Moreover, our simulations on trilayer and tetralayer MnSe show
that achieved HZSS is independent of layer number. These findings establish the
design principle to obtain Zeeman-type splitting in centrosymmetric
antiferromagnets and significantly expand the range of materials to look for
spintronics
Nonrelativistic spin splittings in twisted bilayers of centrosymmetric antiferromagnets: A case study of MnPSe3 and MnSe
Antiferromagnetism-induced spin splittings--even without atomic spin-orbit
coupling--are promising for highly efficient spintronics applications. Although
two-dimensional (2D) centrosymmetric antiferromagnetic materials are abundant,
they have not received extensive research attention owing to PT
symmetry-enforced net zero spin polarization and magnetization. Here, we
demonstrate a paradigm to harness nonrelativistic spin splitting (NRSS) by
twisting the bilayer of type-III centrosymmetric antiferromagnets. We predict
by first-principles simulations and symmetry analysis on prototypes MnPSe3 and
MnSe antiferromagnets (in the monolayer limit) that Rashba-Dresselhaus and
Zeeman-like NRSSs arise along specific paths in the Brillouin zone. The
strength of Rashba-Dresselhaus spin splitting (up to 90 meV{\AA})
induced by twisting is comparable to that of spin-orbit coupling. The results
also demonstrate how applying biaxial strain and a perpendicular electric field
could be envisaged to tune the magnitude of NRSS. The findings reveal the
untapped potential of centrosymmetric antiferromagnets and thus expand the
materials to look for spintronics
Phase-field modeling of electrochemical phenomena
In this article, we review the progress in the field of application of phase-field models for simulating electrochemical phenomena such as etching, electro-deposition, electromigration, intercalation etc. As we will see the present models can be considered as extensions of the already existing models for diffusion coupled phase transformations. We briefly visit the essential thermodynamics of the electrochemical interfaces and the basis of phase-field formulations existing in literature for modeling electrochemical reactions and electromigration. Thereafter, we give a brief overview of the present state of literature in this field
- …