Function Of Lattice Parameter Research Articles

Investigation of Structural with Electronic Properties of Methylammonium Lead Iodide Perovskite Using Density Functional Theory

Employing first-principles calculations based on density functional theory (DFT), we have investigated bulk properties as well as the functions of lattice parameter, unit cell volume calculations, displacement parameter, the interatomic distance, internal bond angle of relevant atoms on the optimized structures where the dependences of k-point summation and cut-off energies with corresponding lattice parameter variations are not dominant. The optimized structure’s property of orthorhombic CH3NH3PbI3 has great similarities with the prevalent experimental and/or theoretical data and shows a direct band gap crystal with a minimum band gap 1.80 eV at the gamma symmetry point.

Molecular beam epitaxy of TmTe thin films on SrF2 (111)

The odd parity nature of 4f states characterized by strong spin–orbit coupling and electronic correlations has led to a search for novel topological phases among rare earth compounds, such as Kondo systems, heavy Fermions, and homogeneous mixed-valent materials. Our target system is thulium telluride thin films whose bandgap is expected to be tuned as a function of lattice parameter. We systematically investigate the growth conditions of TmxTey thin films on SrF2 (111) substrates by molecular beam epitaxy. The ratio between Te and Tm supply was precisely tuned, resulting in two different crystalline phases, which were confirmed by x-ray diffraction and x-ray photoemission spectroscopy. By investigating the crystalline quality as a function of the substrate temperature, the optimal growth conditions were identified for the desired Tm1Te1 phase. Additional low energy electron diffraction and reflective high energy electron diffraction measurements confirm the epitaxial growth of TmTe layers. X-ray reflectivity measurements demonstrate that homogeneous samples with sharp interfaces can be obtained for varied thicknesses. Our results provide a reliable guidance to prepare homogeneous high-quality TmTe thin films and thus serve as a basis for further electronic investigations.

Multiscale Simulation Study on the Anisotropic Behavior of Seamless Copper Tubes Processed under Varied Conditions

One of the most important parameters making the production of precision tubes a challenging process, is the inhomogeneity of mass flow in the pre-stage of processing leading to eccentricity, heterogeneity of residual stresses and crystallographic texture. This paper presents a multiscale modeling framework linking four disparate length scales for studying eccentricity and texture evolution in the tube drawing process with standard as well as tilted dies. The main aim of using this methodology was to comprise the anisotropic elastic and plastic behavior of the material and the crystallographic orientations in the FEM model.This multiscale modeling framework starts with electronic scale calculations using the density functional theory approach to calculate the energy variation as a function of lattice parameters as well as the generalized stacking fault energy for copper. The calculated parameters are bridged to the next simulation scale, the atomic scale calculation. Where molecular dynamics simulations are performed to generate mobilities for dislocations and drag coefficients. The dislocation dynamics approach in the microscale then utilized the mobility values to compute the hardening parameters using the Palm-Voce hardening equation. The use of UMAT subroutine allowed to combine the crystal plasticity theory with the FEM model and calculated elastic and plastic parameters. These last ones were imported to the FEM simulations created for a two-step tube drawing process, performed with standard as well as tilted dies. The simulation results were validated using the measured eccentricity, texture, and mechanical properties: they were in a good agreement with the experimental results.

Thermodynamic stability analysis of Bi-containing III-V quaternary alloys and the effect of epitaxial strain

The thermodynamic stability of Bi-containing III-V quaternary alloys was determined using the delta lattice parameter (DLP) model in conjunction with density functional theory (DFT) calculations. The DLP model and DFT-calculated enthalpy of mixing show remarkably good agreement for the In1-yGayAs1-xBix and GaAs1-x-yBixPy systems. Binodal and spinodal isotherm contours have been constructed for these systems, as well as In1-yGayP1-xBix, In1-yGaySb1-xBix, GaAs1-x-yBixSby, InAs1-x-yBixPy and InAs1-x-yBixSby, for their unstrained and pseudomorphically strained states as a function of lattice parameter. Enhanced Bi solubility can be achieved by epitaxial growth of alloys on substrates with lattice parameters from 0.565 to 0.6058 nm. The incorporation of an anion element with a smaller atomic size also increases the Bi solubility in the Bi low concentration regime. This work elucidates the thermodynamic stability dependence for Bi-containing quaternary alloys on choice of cation, anion and strain state. It also extends the DLP model to a wider composition range.

Tuning magnetic monopole population and mobility in unidirectional array of nanomagnets as a function of lattice parameters

Sets of nanomagnets are often utilized to mimic cellular automata in the design of nanomagnetic logic devices or frustration and emergence of magnetic monopoles in artificial spin ice systems, once that unidirectional arrangement of nanomagnets can behave as artificial spin ice, with frustration arising from second neighbors' dipolar interaction, and present good magnetic monopole mobility due to the low string tension among charges. Here, we present an experimental investigation of magnetic monopole population and mobility as a function of lateral and longitudinal distance among nanomagnets. The observed results could be useful in the nanomagnet logic device design and bring new insights about several possible designs for tuning magnetic monopole unidirectional mobility and transport under a low external magnetic field for further application in magnetricity.

Thermoelectric properties, phase analysis, microstructural investigation and lattice parameters c/a ratio of Al3+ and In3+ dual-doped zinc oxide-based ceramics sintered at high temperature under an argon atmosphere

Composition in (Zn0.98-yIny) (y = 0.05, 0.02, 0.01, 0.005) were fabricated via conventional solid-state sintering route under an argon atmosphere at 1400 °C for 10 h (h) their phases, microstructures and thermoelectrical properties were investigated. Single phase ceramics were formed for the composition with y ≤ 0.05. The highest power factor (PF) of 481.8 µW K−2 m−1 ± 0.2, Seebeck coefficient −98.08 µV K−1 ± 0.2 and electrical resistivity (ρ) of 1.997 mΩ cm ± 0.2 was obtained for x = 0.02, y = 0.005 i.e., (Zn0.975Al0.02In0.005)O. It is studied that PF is a function of lattice parameter c/a ratio. The resistivities of all the compositions were tuned. These tuned resistivities will be helpful for future thermoelectric devices.

Improvement of modified analytic embedded atom method potentials for noble metals and Cu

ABSTRACTThe modified analytic embedded atom model (EAM) potentials considering farther neighbor atoms are improved for the noble metals (Ag, Au, Pt, Pd, Rh) and Cu. We not only adopt an end processing function and an enhanced smooth continuous condition for the pair potential, but also adjust the model parameters of multi-body potential by fitting a cohesive energy, a mono-vacancy formation energy, the Rose equation curve for the cohesive energy as a function of lattice parameter, a structure energy difference, elastic parameters and an equilibrium condition of crystal. The calculation results of structure energy differences misfit the experiment data for the noble metals and Cu in the unimproved EAM, because anyone of these differences have not been considered in the calculation of its model parameters. After the modification, the model showed better simulation results for the noble metals and Cu.

NATURAL ORBITALS IN RELATION TO QUANTUM INFORMATION THEORY: FROM MODEL LIGHT ATOMS THROUGH TO EMERGENT METALLIC PROPERTIES

The review begins with a consideration of three forms of quantum information entropy associated with Shannon and Jaynes. For model two-electron spin compensated systems, some analytic progress is first reported. The Jaynes entropy is clearly related to correlation kinetic energy. A way of testing the usefulness of a known uncertainty principle inequality is proposed for a whole class of model two-electron atoms with harmonic confinement but variable electron-electron interaction. Emerging properties are then studied by reference to bcc Na at ambient pressure and its modeling by "jellium". Jellium itself has collective behavior with changes of the density, especially noteworthy being the discontinuity of the momentum distribution at the Fermi surface. This has almost reduced to zero at rs = 100 a.u., the neighborhood in which the quantal Wigner electron solid transition is known to occur. However, various workers have studied crystalline Na under pressure and their results are compared and contrasted. Work by DFT on K, Rb and Cs is discussed, but now with reduced density from the ambient pressure value. The crystalline results for the cohesive energy of these metals as a function of lattice parameters and local coordination number are shown to be closely reproduced by means of ground and excited states for dimer potential energy curves. Then, pair potentials for liquid Na and Be are reviewed, and compared with the results of computer simulations from the experimental structure factor for Na . Finally, magnetic field effects are discussed. First a phenomenological model of the metal-to-insulator transition is presented with an order parameter which is the discontinuity in the Fermi momentum distribution. Lastly, experiments on a two-dimensional electron assembly in a GaAs / AlGaAs heterojunction in a perpendicular magnetic field are briefly reviewed and then interpreted.

Formation and decay of Bose-Einstein condensates in an excited band of a double-well optical lattice

We study the formation and collision-aided decay of an ultra-cold atomic Bose-Einstein condensate in the first excited band of a double-well 2D-optical lattice with weak harmonic confinement in the perpendicular $z$ direction. This lattice geometry is based on an experiment by Wirth et al. The double well is asymmetric, with the local ground state in the shallow well nearly degenerate with the first excited state of the adjacent deep well. We compare the band structure obtained from a tight-binding (TB) model with that obtained numerically using a plane wave basis. We find the TB model to be in quantitative agreement for the lowest two bands, qualitative for next two bands, and inadequate for even higher bands. The band widths of the excited bands are much larger than the harmonic oscillator energy spacing in the $z$ direction. We then study the thermodynamics of a non-interacting Bose gas in the first excited band. We estimate the condensate fraction and critical temperature, $T_c$, as functions of lattice parameters. For typical atom numbers, the critical energy $k_BT_c$, with $k_B$ the Boltzmann constant, is larger than the excited band widths and harmonic oscillator energy. Using conservation of total energy and atom number, we show that the temperature increases after the lattice transformation. Finally, we estimate the time scale for a two-body collision-aided decay of the condensate as a function of lattice parameters. The decay involves two processes, the dominant one in which both colliding atoms decay to the ground band, and the second involving excitation of one atom to a higher band. For this estimate, we have used TB wave functions for the lowest four bands, and numerical estimates for higher bands. The decay rate rapidly increases with lattice depth, but stays smaller than the tunneling rate between the $s$ and $p$ orbitals in adjacent wells.

Magnetic properties of CrSb compounds with zinc-blende and wurtzite structures

The electronic structure and magnetic properties of Cr–Sb compounds with zinc-blende and wurtzite structure have been studied by means of the Korringa–Kohn–Rostoker (KKR) band structure method. The occurrence of a half-metallic behavior has been investigated for the bulk systems as a function of lattice parameter, as well as for thin films deposited on different substrates. In the latter case the influence of the surface and interface on the electronic structure is discussed in addition. To study magnetic order in the bulk and within the films, exchange coupling parameters have been calculated from first principles. They have been used for subsequent Monte Carlo simulations, based on a classical Heisenberg Hamiltonian, to obtain the Curie temperature.

Classification of super domains and super domain walls in permalloy antidot lattices

We study the remanent domain configurations of rectangular permalloy antidot lattices over a range of lattice parameters. The influence of antidot diameter, antidot spacing, and aspect ratio of the lattice on the remanent domain configuration are investigated by magnetic force microscopy and supported by micromagnetic simulations. In the remanent state, areas of cells with the same orientation of average magnetization form magnetic super domains separated by super domain walls (SDWs). Two types of SDWs are identified. The first type is characterized by low stray field energy, is linear, and expands over many lattice constants. In contrast, the second type shows high stray field energy and is situated at kinks of low energy SDWs. Its width can vary from a minimum of two lattice cells up to several lattice constants, depending on the lattice parameters. The occurrence and structure of these two types of SDWs as functions of lattice parameters are classified and discussed in terms of the interplay of stray field and exchange energy.

Collapse and revival dynamics of number-squeezed superfluids of ultracold atoms in optical lattices

Recent experiments have shown a remarkable number of collapse-and-revival oscillations of the matter-wave coherence of ultracold atoms in optical lattices [Will et al., Nature 465, 197 (2010)]. Using a mean-field approximation to the Bose-Hubbard model, we show that the visibility of collapse-and-revival interference patterns reveal number squeezing of the initial superfluid state. To describe the dynamics, we use an effective Hamiltonian that incorporates the intrinsic two-body and induced three-body interactions, and we analyze in detail the resulting complex pattern of collapse-and-revival frequencies generated by virtual transitions to higher bands, as a function of lattice parameters and mean-atom number. Our work shows that a combined analysis of both the multiband, non-stationary dynamics in the final deep lattice, and the number-squeezing of the initial superfluid state, explains important characteristics of optical lattice collapse-and-revival physics. Finally, by treating the two- and three-body interaction strengths, and the coefficients describing the initial superposition of number states, as free parameters in a fit to the experimental data it should be possible to go beyond some of the limitations of our model and obtain insight into the breakdown of the mean-field theory for the initial state or the role of nonperturbative effects in the final state dynamics.

Simple analytic embedded atom potential for FCC materials

A simple empirical embedded-atom potential that includes a long range force is developed for FCC metals. The potential parameters of this model are determined by fitting lattice constant, three elastic constants, cohesive energy, and vacancy formation energy using an optimisation technique (Arora, 2007). Parameters for Cu, Ag, Au, Al, Ni, Pd and Pt have been obtained. The obtained parameters are used to calculate bulk modulus, divacancy formation energy, and melting point. The predicted values are in good agreement with experimental results. The predicted total energy as a function of lattice parameter is also in good agreement with the equation of state of Rose et al.

Self-propagating high-temperature synthesis of cubic niobium nitride under high pressures of nitrogen

Cubic niobium nitrides δ-NbN x with different x = 0.87–1.015 were prepared by the self-propagating high-temperature synthesis (SHS) under nitrogen pressures of P(N 2) = 48–230 MPa. Nitrogen composition x as a function of P(N 2) was determined in weight gain experiments and compared with that determined by chemical (Kjeldahl) analysis. For powders with different x, the superconducting transition temperature T c was measured as a function of lattice parameter a. The T c values were found to grow linearly with increasing a. A maximum value of T c = 15.0 K for cubic niobium nitride corresponded to a maximum value of a = 4.3901 Å.

Magnetic Properties of Co-Pt Nanopillars as Function of Lattice Parameter and Morphology of Pt Underlayer

Magnetic Properties of Co-Pt Nanopillars as Function of Lattice Parameter and Morphology of Pt Underlayer

Force constants and many-body electrostatic interactions in two-dimensional colloidal crystal

A model of a two-dimensional colloidal crystal with a hexagonal lattice, the electrostatic interactions in which are described by the nonlinear Poisson-Boltzmann equation, is considered. The calculation procedure for force constants of this crystal is treated in detail. Properties of system symmetry, which make it possible to significantly decrease the volume of calculations and to classify force constants, are analyzed. Numerical data for force constants of a crystal as functions of lattice parameters at different particle sizes are reported. A method that allows us to disclose the presence of many-body interactions in a system by the behavior of force constants at some interval of the values of lattice parameters is proposed. The application of this method to the system under consideration demonstrated that electrostatic interparticle interactions in the system cannot be reduced to simply a pair interaction of any kind; the introduction of many-body potentials is required for the adequate representation of the elastic properties of a crystal.

A two-dimensional analytical approach for phase transformations involving an invariant line strain

Crystallographic features of needle- or lath-shaped phases generated from solid-state phase transformations can often be explained from the invariant line concept. This paper presents analytical expressions of crystallographic features, including the orientation relationship, the habit plane orientation and dislocation configuration in the habit plane, based on derivations in both reciprocal and direct spaces in two dimensions (2D). Examples are given by applications to face-centered cubic (fcc)/body-centered cubic (bcc) and bcc/hexagonal close-packed hcp systems, with results which are functions of lattice parameters. These results are consistent with available results from previous studies. Compared to the existing (2D) models for similar conditions, the present approach has overcome the limitation that the invariant line must lie in 2D space and provides a description of the dislocation configuration that was not available in other 2D models. Compared with the three dimensional (3D) O-line approach, the present approach is more transparent and simpler when a 2D treatment is allowed.

The structure properties of LaNi 3.5Al 1.5

The structure properties of LaNi 3.5Al 1.5 have been investigated by the density functional theory using the full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). The elastic constants of LaNi 3.5Al 1.5 are determined by a least-squares fitting of the calculated binding energy with a generalized two dimensional cubic function of lattice parameter a and c . The results show that the calculated lattice parameters ( a = b = 0.5092 nm and c = 0.4214 nm) are in good agreement with the corresponding experimental data, that Al atoms prefer to substitute Ni atoms in the 3g sites and tend to disperse in middle planes. For LaNi 3.5Al 1.5, the bulk modulus (123.1 GPa), the shear modulus (68.6 GPa) and the values of the elastic constants C 11+C 12 (296.2 GPa), C 13 (76.4 GPa) and C 33 (210.5 GPa) are worked out for the first time. The ratio of c/a tends to increase from 0.790 (LaNi 5) to 0.804 (LaNi 4Al) and 0.827 (LaNi 3.5Al 1.5), which indicates that the LaNi 3.5Al 1.5 compound is observed to change less anisotropic with the substitution of Al atoms than the host alloy.

First-principles materials study for spintronics: MnAs and MnN

We report ab-initio all electrons density- functional calculations for the electronic structure of the compounds MnAs and MnN, in the zinc-blende phase. They are potential materials for use in fabrication of new functional semiconductors taking advantage of the spin degree of freedom. The aim is the establishing of the semiconductor spin electronics (spintronics) as a practical technology [H. Ohno, Semiconductor Science and Technology 17, 4 (2002).]. We compare results obtained using the theoretical approaches LDA (Local Density Approximation) and GGA (Generalized Gradient Approximation). The calculations are spin-polarized and we follow the evolution of the band structures as a function of lattice parameter. We compare also the evolution of the density of states of the majority-spins and of the minority-spins. We conclude that, depending on the lattice parameter, both materials may be half-metallic, therefore showing conduction by charge carriers of one spin direction exclusively: the majority- spin band is continuous, while the minority-spin has a gap. Both materials reach a total magnetization of the order of 4 mB. MnN changes from paramagnetic to ferromagnetic with the increase of the lattice parameter.

Larger absolute photonic band gap in two-dimensional air–silicon structures

We investigate different aspects of the absolute photonic band gap (PBG) formation for two-dimensional photonic crystals, consisting of air rods drilled into silicon. Specifically, square lattices of square and circular rods are considered. The lattice symmetry, shape and orientation of the rods affect the photonic gap parameters. A symmetry reduction by addition of a smaller different shaped rod into the center of the lattice unit cell can produce significantly larger band gap. Combining the symmetry reduction and rotation of the noncircular rods yields the greatest improvements in the size of absolute band gap. We discuss the maximization of the absolute PBG width as a function of lattice parameters and the practical fabrication feasibility of these optimized structures.