Optimized Lattice Parameters Research Articles

Fabrication of ZnO photonic crystals by nanosphere lithography using inductively coupled-plasma reactive ion etching with CH4/H2/Ar plasma on the ZnO/GaN heterojunction light emitting diodes

This article reports fabrication of n-ZnO photonic crystal/p-GaN light emitting diode (LED) by nanosphere lithography to further booster the light efficiency. In this article, the fabrication of ZnO photonic crystals is carried out by nanosphere lithography using inductively coupled plasma reactive ion etching with CH4/H2/Ar plasma on the n-ZnO/p-GaN heterojunction LEDs. The CH4/H2/Ar mixed gas gives high etching rate of n-ZnO film, which yields a better surface morphology and results less plasma-induced damages of the n-ZnO film. Optimal ZnO lattice parameters of 200 nm and air fill factor from 0.35 to 0.65 were obtained from fitting the spectrum of n-ZnO/p-GaN LED using a MATLAB code. In this article, we will show our recent result that a ZnO photonic crystal cylinder has been fabricated using polystyrene nanosphere mask with lattice parameter of 200 nm and radius of hole around 70 nm. Surface morphology of ZnO photonic crystal was examined by scanning electron microscope.

Structural, elastic, electronic properties and Fermi surface for superconducting Mo 2GaC in comparison with V 2GaC and Nb 2GaC from first principles

First-principles calculations were performed to investigate structural, elastic and electronic properties of the first discovered superconducting nanolaminate Mo 2GaC in comparison with isostructural Ga-containing phases V 2GaC and Nb 2GaC. As a result, the optimized lattice parameters, independent elastic constants, bulk moduli, compressibility, shear moduli, Young’s moduli and Poisson’s ratio were evaluated. Besides, electronic bands, densities of states (DOS), total and site-projected l-decomposed DOS at the Fermi level, as well as the shapes of the Fermi surfaces for these Ga-containing nanolaminates were obtained and analyzed in comparison with the available theoretical and experimental data.

Structural, elastic, electronic and magnetic properties of perovskite-like Co 3WC, Rh 3WC and Ir 3WC from first principles calculations

We have performed ab initio total energy calculations using the full-potential linearized augmented plane wave method (FP-LAPW) with the generalized gradient approximation (GGA) for the exchange-correlation potential to predict the structural, elastic, cohesive, electronic and magnetic properties of perovskite-like phases Co 3WC, Rh 3WC and Ir 3WC. The optimized lattice parameters, density, independent elastic constants ( C ij), bulk moduli, shear moduli, tetragonal shear moduli, compressibility, and Cauchy pressure, as well as electronic densities of states, cohesive and formation energies, atomic magnetic moments have been obtained and analyzed for the first time.

Nanostructured Pt–Fe/C cathode catalysts for direct methanol fuel cell: The effect of catalyst composition

A series of carbon supported Pt–Fe bimetallic nanocatalysts (Pt–Fe/C) with varying Pt:Fe ratio were prepared by a modified ethylene glycol (EG) method, and then heat-treated under H 2–Ar (10 vol%-H 2) atmosphere at 900 °C. The Pt–Fe/C catalysts were characterized by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), energy dispersive analysis by X-rays (EDX) and induced coupled plasma-atomic emission spectroscopy (ICP-AES). XRD analysis shows that Pt–Fe/C catalysts have small crystalline particles and form better Pt–Fe alloy structure with Fe amount increasing. TEM images evidence that small Pt–Fe nanoparticles homogeneously deposited on carbon support and addition of Fe can effectively prevent Pt particles agglomeration. EDX and ICP-AES show that Fe precursor cannot be fully reduced and deposited on carbon support through the adopted EG reduction approach. The electrochemical surface area of Pt–Fe/C catalyst obtained through hydrogen desorption areas in the CV curve increases with Fe atomic percentage increasing from 0 to ca. 50%, and then decreases with more Fe in the Pt–Fe/C catalyst. RDE tests show that the Pt–Fe/C with a Pt:Fe ratio of 1.2:1 and an optimized lattice parameter of around 3.894 Å has the highest mass activity and specific activity to oxygen reduction reaction (ORR). As cathode catalyst, this Pt–Fe/C (Pt:Fe ratio of 1.2:1) exhibits higher direct methanol fuel cell performance at 90 °C than Pt/C and other Pt–Fe/C catalysts, this could be attributed to its smaller particle size and better Pt–Fe alloy structure.

Elastic and electronic properties of the new perovskite-like superconductor ZnNNi3 in comparison with MgCNi3

Full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential has been applied for the study of structural, elastic, and electronic properties of the newly synthesized nitrogen-containing perovskite-like 3K superconductor ZnNNi3. The optimized lattice parameter, independent elastic constants (C11, C12, and C44), bulk (B), and shear (G) moduli, as well as the band structure, total and site-projected l-decomposed densities of states, the Fermi surface, the Sommerfeld coefficient, and the molar Pauli paramagnetic susceptibility of ZnNNi3 have been evaluated and analyzed in comparison with the related 8K superconductor MgCNi3.

Electronic and elastic properties of perovskite‐like W3NiC, W3NiN and Co3WC from first‐principles calculations

AbstractWe have performed ab initio total energy calculations using the full‐potential linearized augmented plane wave (FP‐LAPW) method with the generalized gradient approximation (GGA) for the exchange–correlation potential to investigate structural, elastic, cohesive, electronic and magnetic properties of the tungsten‐containing perovskite‐like phases W3NiC, W3NiN and Co3WC. The optimized lattice parameters, independent elastic constants (Cij), bulk moduli (B) and shear moduli (G), as well as densities of electronic states and cohesive and formation energies are obtained and analyzed for the first time. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Minimum emittance in storage rings with uniform or nonuniform dipoles

A simple treatment of minimum emittance theory in storage rings is presented, favoring vector and matrix forms for a more concise picture. Both conventional uniform dipoles and nonuniform dipoles with bending radius variation are treated. Simple formulas are given for computing the minimum emittance, optimal lattice parameters, as well as effects of nonoptimal parameters. For nonuniform dipoles, analytical results are obtained for a three-piece sandwich dipole model. Minimization of the effective emittance for light sources is given in detail. Usefulness of gradient and/or nonuniform dipoles for reducing the effective emittance is addressed.

Electronic structure and magnetism in [formula omitted]: An ab initio study

We carry out first principles spin polarized calculations in order to study the electronic structure and magnetism of Ni 0.0625 Zn 0.9375 O compound using density functional theory (DFT) within a plane-wave ultrasoft pseudopotential scheme. The electronic properties of Ni x Zn 1 - x O at a concentration of 6.25% are analyzed using a 2 × 2 × 2 wurtzite ZnO supercell. We optimize the lattice constants of ZnO pure and Ni 0.0625 Zn 0.9375 O . We observe that if one Zn atom is substituted by one Ni atom in the wurtzite ZnO supercell, the lattice parameters decrease slightly some thousandths of angstrom. We also find a stable ferromagnetic state in Ni doped ZnO with a total magnetization of 2.04 μ B per supercell. Using the optimized lattice parameters, we have calculated the band structure and density of states of Ni 0.0625 Zn 0.9375 O .

First-principles study of the structural, electronic, vibrational, and elastic properties of orthorhombic NiSi

We present a study of the structural, electronic, vibrational, and elastic properties of the orthorhombic NiSi structure by means of the density-functional theory and the density-functional perturbative theory, with the Perdew-Burke-Ernzerhof generalized gradient approximation of the exchange-correlation functional, within its spin-polarized version. The optimized lattice parameters, the formation energy, and vibrational properties are found in agreement with experimental data. We show that NiSi is not ferromagnetic, with a low density of states at the Fermi level. Elastic constants have been calculated by means of three different approaches for comparison. In the first two, the calculated energy $E$ is fitted as a function of the deformation, atomic positions are either relaxed or not relaxed during the simulations. Atomic relaxations are shown to modify significantly elastic constants. In the third approach we have related acoustic velocities to elastic constants. NiSi is shown to be highly anisotropic. In particular the linear bulk modulus along $b$ axis is much larger than along other axes. Polycrystalline elastic properties and Debye temperature have been also evaluated for a complete description of elastic properties.

Electronic properties of hexagonal tungsten monocarbide (h-WC) with 3d impurities from first-principles calculations

First-principles FLAPW-GGA calculations have been performed to predict the structural, electronic, cohesive and magnetic properties for hexagonal tungsten monocarbide ( h -WC) doped with all 3 d metals. The optimized lattice parameters, density of states, cohesive and formation energies have been obtained and analyzed for ternary solid solutions with nominal compositions W 0.875 M 0.125 C (where M=Sc, Ti…Ni, Cu). In addition, the magnetic properties of these solid solutions have been examined, and magnetization has been established for W 0.875 Co 0.125 C.

Elastic properties of mono- and polycrystalline hexagonalAlB2-like diborides of s, p and d metals from first-principles calculations

We have performed accurate ab initio total energy calculations using the full-potentiallinearized augmented plane-wave (FP-LAPW) method with the generalized gradientapproximation (GGA) for the exchange–correlation potential to systematicallyinvestigate elastic properties of 18 stable, metastable and hypothetical hexagonal(AlB2-like) metaldiborides MB2, where M = Na, Be, Mg, Ca, Al, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ag and Au. For monocrystallineMB2, the optimized lattice parameters, independent elastic constants(Cij), bulk moduli(B) and shearmoduli (G) are obtained and analyzed in comparison with the available theoretical and experimentaldata. For the first time, numerical estimates of a set of elastic parameters of the polycrystallineMB2 ceramics(in the framework of the Voigt–Reuss–Hill approximation), namely bulk and shear moduli, compressibility(β), Young’s modulus(Y), Poisson’sratio (ν) and Lamécoefficients (μ, λ), are performed.

Elastic properties of quaternary oxypnictides LaOFeAs and LaOFeP as basic phases for new 26–52 K superconducting materials from first principles

The full-potential linearized augmented plane wave method with a generalized gradient approximation for the exchange-correlation potential has been applied to predict the elastic properties of quaternary oxypnictides LaOFe Pn ( Pn = As and P) as the basic phases for the newly discovered 26–52 K superconductors. The optimized lattice parameters, independent elastic constants ( C ij ), bulk moduli, compressibility and shear moduli are evaluated and discussed. Numerical estimates of the elastic parameters of the polycrystalline LaOFe Pn ceramics are performed for the first time.

Elastic and electronic properties of hexagonal and cubic polymorphs of tungsten monocarbide WC and mononitride WN from first‐principles calculations

AbstractWe have performed accurate ab‐initio total energy calculations using the full‐potential linearized augmented plane wave (FP‐LAPW) method with the generalized gradient approximation (GGA) for the exchange‐correlation potential to investigate the elastic, electronic and cohesive properties of hexagonal and cubic polymorphs of WC and WN. The optimized lattice parameters, independent elastic constants (Cij), bulk moduli (B), shear moduli (G), as well as band structure, density of states, electron density distribution and cohesive energies are obtained and analyzed in comparison with the available theoretical and experimental data. In addition, for the first time, the numerical estimates are made for some elastic parameters of the polycrystalline WC and WN ceramics (in the framework of the Voigt–Reuss–Hill approximation), namely bulk and shear moduli, compressibility (β), Young's moduli (Y), Poisson's ratio (ν) and Lamé's coefficients (μ, λ). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic and elastic properties of non-oxide anti-perovskites from first principles: SuperconductingCdCNi3in comparison with magneticInCNi3

Full-potential linearized augmented plane-wave method with the generalized gradient approximation for the exchange-correlation potential has been applied for the comparative study of structural, elastic, and electronic properties of the synthesized non-oxide anti-perovskites: superconducting $\mathrm{Cd}\mathrm{C}{\mathrm{Ni}}_{3}$ and magnetic $\mathrm{In}\mathrm{C}{\mathrm{Ni}}_{3}$. The optimized lattice parameters, independent elastic constants (${C}_{11}$, ${C}_{12}$, and ${C}_{44}$), bulk modules $B$, compressibility $\ensuremath{\beta}$, shear modules $G$, and tetragonal shear modules ${G}^{\ensuremath{'}}$ are evaluated. The numerical estimates of the elastic parameters of the polycrystalline $\mathrm{In}\mathrm{C}{\mathrm{Ni}}_{3}$ and $\mathrm{Cd}\mathrm{C}{\mathrm{Ni}}_{3}$ ceramics are performed. The band structures, total and site-projected $l$-decomposed densities of states, the shapes of the Fermi surfaces, the Sommerfeld coefficients, and the molar Pauli paramagnetic susceptibility for these anti-perovskites are obtained and analyzed in comparison with the available theoretical and experimental data. From our calculations, the stoichiometric $\mathrm{Cd}\mathrm{C}{\mathrm{Ni}}_{3}$ and $\mathrm{In}\mathrm{C}{\mathrm{N}}_{3}$ are very much alike in both structural and elastic properties but differ in electronic properties. For $\mathrm{In}\mathrm{C}{\mathrm{Ni}}_{3}$, the defect-induced magnetism associated with the indium vacancies or Ni atoms substituting for In was found.

Electronic and vibrational properties of nickel sulfides from first principles

We report the results of first-principles calculations (generalized gradient approximation-Perdew Wang 1991) on the electronic and vibrational properties of several nickel sulfides that are observed on Ni-based anodes in solid oxide fuel cells (SOFCs) upon exposure to H2S contaminated fuels: heazlewoodite Ni3S2, millerite NiS, polydymite Ni3S4, and pyrite NiS2. The optimized lattice parameters of these sulfides are within 1% of the values determined from x-ray diffraction. The electronic structure analysis indicates that all Ni-S bonds are strongly covalent. Furthermore, it is found that the nickel d orbitals shift downward in energy, whereas the sulfur p orbitals shift upward with increasing sulfur content; this is consistent with the decrease in conductivity and catalytic activity of sulfur-contaminated Ni-based electrodes (or degradation in SOFC performance). In addition, we systematically analyze the classifications of the vibrational modes at the point from the crystal symmetry and calculate the corresponding vibrational frequencies from the optimized lattice constants. This information is vital to the identification with in situ vibrational spectroscopy of the nickel sulfides formed on Ni-based electrodes under the conditions for SOFC operation. Finally, the effect of thermal expansion on frequency calculations for the Ni3S2 system is also briefly examined.

First-principles calculations of the elastic and electronic properties of the cubic perovskites SrMO 3 (M = Ti, V, Zr and Nb) in comparison with SrSnO 3

We have performed accurate ab initio total energy calculations using the full-potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential to investigate the systematic trends for structural, elastic and electronic properties of cubic SrMO 3 perovskites' family depending on the type of M cations (d 0: Ti, Zr, d 1: V, Nb and p: Sn). The optimized lattice parameters, independent elastic constants ( C 11, C 12 and C 44), bulk modulus ( B), compressibility ( β), shear modulus ( G), Young's modulus ( Y), Poisson's ratio ( ν), Lamé's coefficients ( μ, λ), as well as band structure, density of states and electron density distributions are obtained and analyzed in comparison with the available theoretical and experimental data. For the first time the numerical estimates of elastic parameters of the polycrystalline SrMO 3 ceramics (in framework of the Voigt–Reuss–Hill approximation) are performed.

Structural, elastic and electronic properties of superconducting anti-perovskites MgCNi3, ZnCNi3 and CdCNi3 from first principles

First principle total energy calculations using the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential were performed to investigate the systematic trends for structural, elastic and electronic properties of the family of superconducting anti-perovskites MCNi3 depending from the type of M cations (M are Mg, Zn and Cd). In result the optimized lattice parameters, independent elastic constants (C11, C12 and C44), bulk modulus B, compressibility β, shear modulus G and tetragonal shear modulus G′ are evaluated. Further, for the first time the numerical estimates of a set of elastic parameters (bulk and shear modulus, Young’s modulus Y, Poisson’s ratio (ν), Lamé’s coefficients (μ, λ)) of the polycrystalline superconducting MCNi3 ceramics (in framework of the Voigt–Reuss–Hill approximation) were performed. Besides, the band structures, densities of states (DOS), total and site-projected l-decomposed DOS at the Fermi level, the shapes of the Fermi surfaces, the Sommerfeld’s coefficients and the molar Pauli paramagnetic susceptibility for these anti-perovskites were obtained and analyzed in comparison with the available theoretical and experimental data.

The effect of B site cations on the properties of para-electric KTa 1/2Nb 1/2O 3 crystal from first-principles calculations

Density functional theory was used to investigate the effect of B site cations on the electric structures and optical properties of para-electric solid solution KTa 1/2Nb 1/2O 3 (KTN) crystal. Three possible arrangements of B site cations (Mode A, Mode B, and Mode C) were presented. The geometry optimization was performed and stable para-electric ground states were obtained for three modes. The optimized lattice parameters are in good agreement with the experimental values. The density of states (DOS) and imaginary parts of dielectric function together with absorption coefficient are determined. The partial DOS of the B site cations are also different for three modes. It is found that KTN has anisotropic optical responses in Mode A and Mode B, and isotropic optical responses in Mode C. Therefore the B site cations influence the properties of KTN obviously.

The effect of B site cations on optical properties of paraelectric KTa1/2Nb1/2O3 crystal

Abstract The effect of B site cations on the optical properties of paraelectric solid solution KTa1/2Nb1/2O3 crystal has been studied by means of density functional theory. Three arrangements of B site cations are presented. The optimized lattice parameters are in good agreement with the experimental values. Reflectivity, refractive index and optical conductivity are investigated. The calculated optical properties are very close to the results of other researchers. It is found that the B site cations ordering obviously influences the optical properties of KTN crystal.

First-principles study of the cubic perovskitesBiMO3(M=Al, Ga, In, and Sc)

We systematically investigated the structure, electronic properties, zone-center phonon modes, and structure instability of four cubic perovskite $\mathrm{Bi}M{\mathrm{O}}_{3}$ compounds, with three of the $M$ ions being IIIB metals (Al, Ga, and In) and one IIIA transition-metal Sc, using first-principles density-functional calculations. Optimized lattice parameters, bulk moduli, band structures, densities of states, as well as charge density distributions are calculated and compared with the available theoretical data. Our results are in good agreement with those previously reported in the literature. All the $\mathrm{Bi}M{\mathrm{O}}_{3}$ oxides considered in the present work are semiconductors with an indirect band gap between the occupied $\mathrm{O}\phantom{\rule{0.2em}{0ex}}2p$ and unoccupied $\mathrm{Bi}\phantom{\rule{0.2em}{0ex}}6p$ states varying between 0.17 and $1.57\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Their electronic properties are determined mainly by Bi--O bonding, which, in turn, depends on the $M--\mathrm{O}$ bonding. Ferroelectric properties of these oxides come from the $6{s}^{2}$ lone pair on the $A$-site Bi ion and is similarly affected by the $M$ ions through their influence on the Bi--O bonding, as suggested by our calculations of density of state, Born effective charge, and soft modes. The existence of soft modes and eight [111] minima suggests that the phase transition in $\mathrm{Bi}\mathrm{Al}{\mathrm{O}}_{3}$ has a mixed displacive and order-disorder character. There is evidence that ferroelectricity is absent in $\mathrm{Bi}\mathrm{Ga}{\mathrm{O}}_{3}$. Our investigation suggests that the $\mathrm{Bi}M{\mathrm{O}}_{3}$ oxides or their modified versions are promising ferroelectric, piezoelectric, multiferroic, and photocatalytic materials.