High-pressure polymorphism of As2S3 and new AsS2 modification with layered structure

At normal pressure, the As₂S₃ compound is the most stable equilibrium modification with unique layered structure. The possibility of high-pressure polymorphism of this substance remains questionable. Our research showed that the As₂S₃ substance was metastable under pressures P > 6 GPa decomposing into two high-pressure phases: As₂S₃ → AsS₂ + AsS. New AsS₂ phase can be conserved in the single crystalline form in metastable state at room pressure up to its melting temperature (470 K). This modification has the layered structure with P12₁1 monoclinic symmetry group; the unit-cell values are a = 7.916(2) Å, b = 9.937(2) Å, c = 7.118(1) Å, β = 106.41° (Z = 8, density 3.44 g/cm³). Along with the recently studied AsS high-pressure modification, the new AsS₂ phase suggests that high pressure polymorphism is a very powerful tool to create new layered-structure phases with “wrong” stoichiometry.     

Electronic structure of CuN3(I)

Self-consistent calculations of the electronic structure of monovalent copper azide CuN₃(I) are carried out in the framework of the density functional theory in the basis set of pseudoatomic orbitals. The specific features of the band structure and the effect of Cu d states on the formation of the energy spectrum of CuN₃(I) are considered. The structure of chemical bonding is analyzed using electron density maps.     

Electronic structure and decomposition pathways of monoammoniate of lithium borohydride Li(NH3)BH4: A first-principles investigation

The monoammoniate of lithium borohydride (Li(NH₃)BH₄) is a potential candidate for hydrogen storage owing to its high hydrogen capacity (18 wt%). In this work, electronic structure, bonding characters, and decomposition pathways of Li(NH₃)BH₄ are investigated from first-principles calculations. We find that NH₃ molecules are covalently attached to Li atoms through N atoms and the ionization of Li atoms plays an essential role in stabilizing the compound. A general correlation between the stability of X(NH₃)BH₄ (X=H,Li,Na,K) and the electronegativities of $X$ atoms is established. The thermal stability of X(NH₃)BH₄ could be modulated by manipulating the cation electronegativities. Free energy computations indicate that Li(NH₃)BH₄→LiBH₄+NH₃ is the most likely thermal decomposition route.     

Electronic structure of the trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta)

The low-energy electronic structure of the nearly optimally doped trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta) is investigated by angle-resolved photoemission spectroscopy. The normal state quasiparticle dispersion and Fermi surface and the superconducting d-wave gap and coherence peak are observed and compared with those of single- and bilayer systems. We find that both the superconducting gap magnitude and the relative coherence-peak intensity scale linearly with T(c) for various optimally doped materials.     

Electronic structure of SiO2(111) thin film

The electronic structure of (111) surface of β-crystobalite is investigat ed using the empirical tight binding method. Our calculations identify surface states in the conduction band, band gap and valence band. The surface state formed from silicon-s and p_z orbitals, which is believed to account for the structure in the O K excitation spectra, lies in the band gap. It is seen that oxygen adsorption on the surface removes surface states and gives rise to a sharp peak at about — 3.8 eV below the valence band edge.     

Electronic structure and optical properties of Sn_(2x)Ga_(2(1-x))O_3 compounds

Band structure, density of states, electron density difference, and optical properties of intrinsic β-Ga2O3 and Sn2xGa2(1-x)O3 (x= 3.125%-6.25%) compounds are studied using first-principle calculations based on the density functional theory. The anisotropic optical properties are investigated by means of the complex dielectric function, which are explained by the selection rule of band-to-band transitions. All the calculation results indicate that the conductivity of Sn2xGa2(1-x)O3 is super to β-Ga2O3, and ...     

Electronic structure of (LaSr)2CuO4 and (NdCe)2CuO4

The electronic structure of (LaSr)₂CuO₄ and (NdCe)₂CuO₄ are compared. It is concluded that in both materials after doping by holes and electrons respectively the Fermi energy is at the top of the valence band. This explains many symmetrical properties and in particular the photoemission experiments.Dedicated to Prof. P. Kienle on the occasion of his 60th birthday     

High-pressure structure and elastic properties of tantalum single crystal:First principles investigation

Since knowledge of the structure and elastic properties of Ta at high pressures is critical for addressing the recent controversies regarding the high-pressure stable phase and elastic properties, we perform a systematical study on the highpressure structure and elastic properties of the cubic Ta by using the first-principles method. Results show that the initial body-centered cubic phase of Ta remains stable even up to 500 GPa and the high-pressure elastic properties are excellently consistent with the available experimental results. Besides, the high-pressure sound velocities of the single- and polycrystals Ta are also calculated based on the elastic constants, and the predications exhibit good agreement with the existing experimental data.     

Electronic structure and spin relaxation of Fe(III) in LiNbO3

Crystal field parameter have been determined from EPR spectra (77K) of LiNbO₃Fe(III). Anomalous line shapes are described phenomenologically and saturation studies are compared with calculations using a second order dynamic spin-hamiltonian H. Mössbauer spectra of LiNbO₃Fe(III) have been interpreted by means of simulations using Liouville superoperators including a static fine-and a hyperfine spin-hamiltonian and H. Calculations have been performed using an effective spin of 1/2, the supermatrix with dimension 288 and a reduced formalism (supermatrix with dimension 96).     

Photon transitions in Upsilon(2S) and Upsilon(3S) decays

We have studied the inclusive photon spectra in Upsilon(2S) and Upsilon(3S) decays using a large statistics data sample obtained with the CLEO III detector. We present the most precise measurements of electric dipole (E1) photon transition rates and photon energies for Upsilon(2S) --> gammachi(bJ)(1P) and Upsilon(3S) --> gammachi(bJ)(2P) (J = 0, 1, 2). We measure the rate for a rare E1 transition Upsilon(3S) --> gammachi(b0)(1P) for the first time. We also set upper limits on the rates for the hindered magnetic dipole (M1) transitions to the eta(b)(1S) and eta(b)(2S) states.     

Electronic band structure and Li diffusion paths in (LaLi)TiO3

The electronic structure and the Li diffusion paths in the lithium doped lanthanum titanate have been studied. The band dispersion and the density of states (DOS) are calculated using the linear-muffin-tin-orbital (LMTO) method. The model structure used contains La-rich and La deficient layers, with the 2a_p × 2a_p × 2a_p unit cell and base centered C symmetry. The primitive cell contains 20 atoms represented by La₃LiTi₄O₁₂. The energy contour map, where Li ions are assumed to move within the La-deficient (002) layer, shows that the stable position of Li ions is off centers of the vacant La sites and that Li ions migrate through the bottlenecks at 2c sites surrounded by four oxygen ions.     

Electronic structure and local interactions on a S(100) 2×1 surface with submonolayer Ba overlayers

The electronic structure and ionization energy for the system Ba/Si(100)2×1 have been studied as functions of the submonolayer coverage. It is found that there is an energy gap in the surface states spectrum and that the Ba/Si(100)2×1 interface is semiconducting up to 1.5 monolayers of Ba. Two surface bands induced by Ba adsorption have been detected. The evolution of the spectrum with increasing degree of Ba coverage points to the existence of two nonequivalent “adsorption sites,” which differ in binding energy by 0.11 eV. The development of the Ba-induced bands is found to terminate at a coverage corresponding to the minimum ionization energy and close to one monolayer. The adsorption bond is shown to have a primarily covalent character. Zh. éksp. Teor. Fiz. 114, 2145–2152 (December 1998)     

Electronic structure and lattice dynamics of Li2Ni(WO4)2

We combined spectroscopic ellipsometry and Raman scattering measurements to explore the electronic structure and lattice dynamics in Li₂Ni(WO₄)₂. The optical absorption spectrum of Li₂Ni(WO₄)₂ measured at room temperature presents a direct optical band gap at 2.25 eV and two bands near 5.2 and 6.0 eV, which are attributed to charge-transfer transitions from oxygen 2p states to nickel 3d or tungsten 5p states. The Raman scattering spectrum of Li₂Ni(WO₄)₂ measured at room temperature presents seventeen phonon modes at approximately 112, 143, 193, 222, 267, 283, 312, 352, 387, 418, 451, 476, 554, 617, 754, 792, and 914 cm⁻¹. When the temperature is decreased to 20 K, the frequency, linewidth, and normalized intensity of all phonon modes exhibited almost no temperature dependence. Upon cooling across 13 K, which is the antiferromagnetic phase transition temperature, the oxygen octahedra stretching mode at 914 cm⁻¹ exhibited a softening and an increase in intensity, thus suggesting a coupling between the magnetic and lattice degrees of freedom. The spin-phonon coupling constant was estimated to be 0.94 mRy/Ų, indicating a weak spin-phonon interaction in Li₂Ni(WO₄)₂.     

ELECTRON MOMENTUM SPECTRA OF EXCITED He(2~1S) AND He(2~3S)

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