查看更多>>摘要：Determining microscopic origin of electronic conductivity in strontium ferrites is a pivotal step toward accomplishing control of a reversible topotactic phase transformation. This functionality is essential for use of these oxides in resistive switching non-volatile memory devices and future neuromorphic computing. Here, we use first principles computations for in-depth study of native defects and their effect on electronic structure in SrFeO2.5. We elucidate the role native defects play and show that an uptake of oxygen in diluted concentrations leads to a p-type conductivity in the SrFeO2.5. We identify two acceptor defect transition states at 0.25 eV for atomic and 0.1 eV for molecular oxygen interstitials.
Abdullahi, Yusuf ZuntuVatansever, Zeynep DemirAkturk, EthemAkinci, Umit...
8页
查看更多>>摘要：We identify a new two-dimensional (2D) tetragonal phase of transition metal alloyed boron-carbide (t-CrFeBC) sheet through combined first-principles calculations and Monte Carlo (MC) simulations. The t-CrFeBC sheet prefers a ferromagnetic ground state with the metallic electronic property. Also, the t-CrFeBC sheet is dynamically and thermally stable. t-CrFeBC exhibits sizable magnetic anisotropy energy (MAE) of 120 mu eV per CrFe alloy with an in-plane easy axis (EA) magnetization direction. Moreover, hysteresis loops and other hysteresis related properties (coercivity and remanent magnetization) which are evidence of existence of ferromagnetism in the tCrFeBC sheet are presented for a wide range of temperature. MC simulation results indicate that t-CrFeBC sheet is soft magnetic material with a small coercieve field and narrow rectangular shaped hysteresis curve near the room temperature. All results show that 2D t-CrFeBC sheet holds a unique promise for advanced magnetic device applications.
查看更多>>摘要：We introduce a machine-learning interatomic potential for bcc iron based on the moment tensor potential framework and a hybridization scheme of distinct sub-potentials. With an orientation on radiation damage effects, the potential shows good transferability from properties relevant to collision cascade to those relevant to plasticity. Specifically, the potential accurately reproduces the short-range repulsive interactions, the generalized stacking fault energies, the dislocation core structures and the formation energies of defect clusters. The general purposed applicability of the potential enables simulation of radiation damage effects in bcc iron with an accurate and an unprecedentedly unified theoretical model.
查看更多>>摘要：The geometric structural optimization and electronic properties of double-walled silicon nanotubes (DWSiNTs) (4,min)@(8,mout) (min = 0 to 4, mout = 0 to 8) are studied in terms of the self-consistent charge density functional tight binding (SCC-DFTB) method. Calculations demonstrate that the regularity of the atomic arrangement, the diameter of the inner and outer walls, the degree of buckling, stability, energy gap, Fermi energy level, quantum molecular descriptors, and charge distribution strongly depend on the chiral index of the tube. In particular, the possibility of tuning the band structure by changing the chiral index has been demonstrated to help for the performance needs of different devices, inducing a metal-semiconductor transition and direct-indirect band gap transition. In addition, the influence of adding an external electric field on electronic properties of the zigzag DWSiNT (4,0)@(8,0) has been investigated. The tube applied electric field transforms from semiconductor to semi-metallic property. The tube becomes metallic upon the critical electric field strength of 0.7 V/nm and 1.0 V/ nm. As increasing the external field strengths, the stability of the tube is reduced and the EF level is increased. The direction of charge transfer is always in the reverse of the field direction, which is different from the case of absent field.
查看更多>>摘要：We present ESpinS (Esfahan Spin Simulation) package to evaluate the thermodynamic properties of spin systems described by a spin model Hamiltonian. In addition to the Heisenberg exchange term, the spin Hamiltonian in ESpinS can contain interactions such as bi-quadratic, Dzyaloshinskii-Moriya, and single-ion anisotropy. By applying the classical Monte Carlo simulation, ESpinS simulates the behavior of spin systems with respect to temperature. ESpinS can calculate the specific heat, susceptibility, staggered magnetization, energy histogram, fourth-order Binder cumulants, and neutron scattering structure factor. Further, it can compute the user-defined magnetic order parameter, that is, the summation of the projection of spins on the user-defined directions and the physical quantities based on it. ESpinS works with both a local update algorithm and a parallel tempering algorithm. The latter is an appropriate option for considering frustrated and spin-glass magnetic systems. ESpinS is written in Fortran 90 and can be run in single or parallel mode. The package is freely available under the GPL license (https://github.com/nafiserb/ESpinS).
查看更多>>摘要：Lithium phosphorus oxy-nitride (LiPON) is a candidate solid electrolyte material for potential use in rechargeable lithium-ion batteries. The use of density functional theory simulations has allowed us to gain atomic-scale insight into the defect properties, solution of dopants and incorporation of lithium in LiPON. The Li2O Schottky is the most favourable disorder process in this material ensuring the formation of Li and O vacancies which are in turn required for vacancy mediated self-diffusion. The Na, As and S are the promising isovalent dopants that can be substituted on the Li, P and O sites respectively. The doping of Mg on the Li site leads to the formation of Li vacancies in LiPON. The promising dopant on the P site to create Li interstitials and oxygen vacancies is the Ge. The stability of the crystal structure upon Li incorporation (up to four Li) was considered. The incorporation confirmed the formation of Li+ ions and expanded the volume of the lattice. Incorporation of multiple Li atoms is more favourable than a single Li incorporation. The band gap of this material decreases upon of Li incorporation without changing its insulating character.
查看更多>>摘要：Spalling behavior of multilayered materials has a tight correlation with shockwave loading conditions and heterointerfaces. Here, the dynamic response and spallation of [111] Cu/Ni nano-multilayered system under different shock pulse duration are investigated by molecular dynamics. Our work suggests that spallation occurs only in the Cu region instead of in Ni. Also, spalling mechanism transit from homogenous nucleation of voids within Cu layers to nucleation at Cu/Ni interfaces with growing shock duration, resulting in the drop of global spall strength. The recompaction result from the compressive wave is observed to blocks the cavitation's aggregation, which proves the possibility of damage controlling by interface and impedance design at the atomic scale. Additionally, dislocation analysis shows a similar evolving process of dislocations in Cu and Ni. Longer shock duration is found to result in lower peak density of stair-rods.
查看更多>>摘要：The electronic structure of doped Fe-Ga alloy is investigated theoretically using methods of the density functional theory. The work aims to uncover the difference in the material's magnetostrictive properties when doping with transition metals or La as the simplest representative of rare-earth elements. The effect understudy was investigated by considering the change in two features of the electronic structure caused by doping: the density of d-states on Fe atoms and the nature of the Fe-Fe bonding near the doping atom. The transition metal atoms are surrounded by Fe atoms with a low-density d-states, eliminating the doping effect. The interatomic bonds of transition metals with the nearest Fe atoms have an antibonding character, while bonds between Fe atoms of the first and second coordination spheres are more binding than in an undoped alloy. This effect leads to magnetostriction decrease. In the La-doped alloy, the opposite picture is found. An increase in magnetostriction should occur due to the enhancement of the antibonding character of bonds between Fe atoms in the first and second coordination spheres of the dopant.
查看更多>>摘要：Directed energy deposition (DED) is an advanced additive manufacturing technology for the fabrication of near -net-shape metal parts with complex geometries and high performance metrics. Studying the grain structure evolution during the process is pivotal to evaluating and tailoring the as-built products' mechanical properties. However, it is time-consuming to simulate the multi-layer deposition process using the physics-based numerical model to optimize the process parameters for achieving the desired microstructure. In this paper, a physics-informed machine learning algorithm to predict the grain structure in the DED process is proposed. To generate training data for the machine learning algorithm, we use an experimentally validated cellular automaton finite volume method (CAFVM) for DED Inconel 718, where CA is applied to model the grain structure and FVM to simulate the heat transfer. We develop a neural network model to identify the correlation between the local thermal features and their corresponding grain structure characteristics. The inputs and outputs of the neural network (NN) model are selected based on the governing physics, and a novel way to extract them is proposed. The NN model can quickly predict the grain structure characteristics with the local thermal data for thin-wall builds, and the predictions are in good agreement with the numerical simulation results. We expect the proposed method can benefit other metal additive manufacturing technologies to formulate efficient and accurate process-structure relationships and in-process feedback control.
NSTL
Elsevier