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 P^T^\mathcal{\hat{P}\hat{T}}-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 $~\sim$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