Kinds Of Local Structures Research Articles

Tetrad extremal field-gauge vector structure

In previous works, we have proven that there are local tetrads in four-dimensional curved Lorentzian spacetimes that can be written in terms of two kinds of local structures, the skeletons and the gauge vectors. These tetrads diagonalize locally and covariantly the stress–energy tensors for systems of differential equations of the Einstein–Maxwell kind in the Abelian electromagnetic case, or of the Einstein–Maxwell–Yang-Mills kind when non-Abelian Yang–Mills fields are included, along with suitable Yang–Mills stress–energy tensors. Under local Lorentz transformations, these new tetrads conserve their skeleton-gauge vector structure. In this short paper, we will prove that given any general unit orthogonal tetrad in spacetime, we will be able to construct a new tetrad in the skeleton-gauge vector form. We will prove a theorem stating that the original orthonormal tetrad can be constructed or reexpressed with this same local tetrad skeleton-gauge vector structures. The theorems proved in this paper will enable the demonstration of new results in group isomorphism theorems in the future.

P7] Intrinsic defects in ammonia borane: density functional theory calculations augmented with van der Waals correction

Structural, electronic and energetics properties of Nb-doped LiBH4 (010) surface have been studied based on the first-principles density functional theory calculations. Three kinds of local structures are found during the dehydrogenation reaction of LiBH4, the most two favorable hydrogen desorption pathways are found to lead to NbH2-BH2-(BH4)3 complex when the Nb occupies the top site of single B atom and lead to NbH2-(BH3)2 complex when the Nb occupies the bridge site of two adjacent B atoms. The formation of NbH2 and BH2 units in the NbH2-BH2-(BH4)3 complex as well as the catalytic effect of Nb on the structures of surrounding (BH4)− units due to the orbital overlaps between Nb and inner B-H bonds in the complex. For the NbH2-(BH3)2 complex, NbH2 and NbB2 phases may be formed in sequence accompanied by the dehydrogenation reaction. The results are in good agreement with the report of Wang, KK et al. experimentally. The calculated average hydrogen desorption energies of Nb-doped LiBH4 (010) surface are smaller than the pure LiBH4 (010) surface about 1.7 eV and 1.5 eV, respectively. These properties reveal that the import of Nb has great effect on reducing the bond strength of B-H.

Nb-doped LiBH4 (010) surface for hydrogen desorption: First-principles calculations

Structural, electronic and energetics properties of Nb-doped LiBH4 (010) surface have been studied based on the first-principles density functional theory calculations. Three kinds of local structures are found during the dehydrogenation reaction of LiBH4, the most two favorable hydrogen desorption pathways are found to lead to NbH2-BH2-(BH4)3 complex when the Nb occupies the top site of single B atom and lead to NbH2-(BH3)2 complex when the Nb occupies the bridge site of two adjacent B atoms. The formation of NbH2 and BH2 units in the NbH2-BH2-(BH4)3 complex as well as the catalytic effect of Nb on the structures of surrounding (BH4)− units due to the orbital overlaps between Nb and inner B-H bonds in the complex. For the NbH2-(BH3)2 complex, NbH2 and NbB2 phases may be formed in sequence accompanied by the dehydrogenation reaction. The results are in good agreement with the report of Wang, KK et al. experimentally. The calculated average hydrogen desorption energies of Nb-doped LiBH4 (010) surface are smaller than the pure LiBH4 (010) surface about 1.7 eV and 1.5 eV, respectively. These properties reveal that the import of Nb has great effect on reducing the bond strength of B-H.

Microscopic characterization of polarization fatigue in ferroelectric vinylidene fluoride and trifluoroethylene copolymer films

Recently studies on electric fatigue in ferroelectric polymers have drawn much attention due to the potential application of ferroelectric polymers in nonvolatile memory devices. Compared to inorganic ferroelectrics, ferroelectric polymers are mostly semi-crystalline with a coexistence of crystalline phase and amorphous phase. To well understand electric fatigue in ferroelectric polymers, it is necessary to determine the different contributions from crystallites, amorphous phase and even boundaries between crystallites to polarization fatigue. Here we introduce a SPM-based technique to characterize electric fatigue in nanometer scale. Microscopic fatigue is determined by the attenuation of voltage-excited local vibration amplitudes at two kinds of local structures (the crystallites and the boundaries between crystallites), and, for comparison, macroscopic electric fatigue characteristics are also recorded by a standard Sawyer–Tower circuit. Our observations indicate that the attenuation rate of vibration amplitude on crystallites is much slower than that at boundaries. Abnormal increase of vibration amplitude and slim local butterfly loops are observed at some of boundaries in deeply fatigued films.

Synthesis of single-phase carbon nitride film prepared by hot implantation

High temperature ion implantation (hot implantation) is used to synthesize carbon nitride (CN x ) films. Three CN x films are compared by near edge X-ray absorption fine structure (NEXAFS) spectroscopy; one is prepared by room temperature implantation, another is prepared by subsequent annealing, and the other is prepared by hot implantation. The former two films show three comparable discrete peaks in N K-edge NEXAFS spectra, which are assigned to different kinds of local structures at N sites. On the other hand, a single peak grows predominantly in the spectra for the film prepared by hot implantation. Through the polarization dependence analysis of NEXAFS, the dominant peak is assigned to the fullerene-like structure of CN x which consists of pentagons and hexagons. The difference between the CN x films which are synthesized by subsequent annealing and hot implantation is also discussed.

Effect of Chromium Substitution on the Lattice Vibration of Spinel Lithium Manganate: A New Interpretation of the Raman Spectrum of LiMn2O4

The variation of the lattice vibration of spinel lithium manganate upon chromium substitution has been investigated by performing a combinative micro-Raman and X-ray absorption spectroscopic (XAS) analysis. As the manganese ion in the spinel LiMn2-xCrxO4 is replaced by a chromium ion, the relative intensities of two main Raman peaks at ∼580 and ∼620 cm-1 are remarkably changed. This change cannot be understood by the previous peak assignment on the basis of the average crystal structure of the cubic spinel lattice. According to the Mn K-edge XAS analysis, it is certain that there are two kinds of local structures around the manganese in the spinel LiMn2-xCrxO4 and the substitution of Mn with Cr gives rise to a depression of the local tetragonal distortion around the manganese ion. On the basis of this finding, we are able to re-interpret two main Raman features of the cubic spinel lithium manganate as totally symmetric A1g modes without and with tetragonal distortion, respectively. This new interpretation is further supported not only by the comparison with the reference spectra of λ-MnO2 and Li2Mn2O4 but also by the good correlation between the ratio of Mn+IV/Mn+III concentration and the relative intensities of two Raman peaks.

Local Atomic Arrangement and Electronic Structure of Nanocrystalline Transition Metal Oxides Determined by X-ray Absorption Spectroscopy

The local crystal structure and electronic configuration of transition metal in X-ray amorphous MnO2 and CrO2 nanocrystals have been examined by using X-ray absorption (XAS) spectroscopy at Mn K and Cr K-edges. The Mn K-edge XAS study reveals that tetravalent manganese ions are stabilized in α-MnO2-type local atomic arrangement consisting of the intergrowth of edge- and corner-shared MnO6 octahedra. On the other hand, it is found from Cr K-edge XAS results that nanocrystalline CrO2 possesses two different kinds of local structures around chromium, that is, Cr2O3-type with octahedral site and CrO3-type with tetrahedral site. The presence of Cr+VI species on the surface would be helpful for Li grafting process, giving rise to excellent electrochemical performances. This work can be regarded as a strong evidence for the usefulness of XAS to study nanocrystalline electrode materials.

グラファイト単結晶中に注入したシリコンの局所構造

Solid carbon forms two kinds of local structures, i.e., diamond-like and two-dimensional graphite structures. In contrast, silicon carbide tends to prefer only diamond structure that is composed of sp3 bonds. In order to clarify whether or not two-dimensional graphitic SixC layer exists, we investigate the local structures of SixC layer produced by Si+-ion implantation into highly oriented pyrolitic graphite (HOPG) by means of near-edge X-ray absorption fine structure (NEXAFS). The energy of the resonance peak in the Si K-edge NEXAFS spectra for Si+-implanted HOPG is lower than those for any other Si-containing materials. The intensity of the resonance peak showed a strong polarization dependence. These results suggest that the final state orbitals around Si atoms have π*-like character and the direction of this orbital is perpendicular to the graphite plane. It is elucidated that the Si-C bonds produced by the Si+-ion implantation are nearly parallel to the graphite plane, and SixC phase forms a two-dimensionally spread graphite-like layer with sp2 bonds.

The optically active center and its activation process in Er-doped Si thin film produced by laser ablation

The local structure of erbium-doped silicon produced by the laser ablation technique is investigated by Er LIII-edge x-ray absorption fine structure analysis. The combined analysis of extended x-ray absorption fine structure analysis and an x-ray absorption near-edge structure simulation based on multiple-scattering theory reveals the most probable atomic coordination of the optically active center; Er bonded with six oxygen atoms has a C4v symmetry. The optical activation process of this system is also discussed. The Si target with 10 wt% Er2O3 has two kinds of local structures, C-rare-earth Er2O3 grain and another Er phase incorporated in Si. The laser ablation homogenizes these phases, and deposits a new single-phase structure of the octahedron (Oh point group) on the substrates. In this phase, the optical transition probability is low due to the forbidden 4f transition of Er in the crystal field originating from the higher-order symmetry of O. After annealing, degradation of the symmetry from Oh to C4v results in a crystal field suitable for inducing sufficient radiation transition.

A Study of Local Structure Formation in Binary Solutions of 2-Butoxyethanol and Water by Rayleigh Scatterring and Raman Spectra

Abstract The concentration dependence of concentration fluctuations at 21, 32, and 42 °C and of Raman spectra at 21 °C were measured for binary solutions of 2-butoxyethanol (BE) and water. The existence of the two kinds of local structures is inferred; clathrate hydrate-like structure g[(H2O)50BE] and aggregate h[(H2O)4BE]. The compositions of these two structures are the same as those of the two phases into which the solution separates above the critical solution temperature. The phase separation is understood to be the end of the growth of the local structures, which already exist well below the critical solution temperature.