Search results for "Band structure"
showing 10 items of 215 documents
Luminescence of GeO2 glass, rutile-like and α-quartz-like crystals
2006
Abstract The luminescence of GeO 2 rutile-like crystals was studied. Crystals were grown from a melt of germanium dioxide and sodium bicarbonate mixture. Luminescence of the crystal was compared with that of sodium germanate glasses produced in reduced and oxidized conditions. A luminescence band at 2.3 eV was observed under N 2 laser (337 nm). At higher excitation photon energies and X-ray excitation an additional band at 3 eV appears in luminescence. The band at 2.3 eV possesses intra-center decay time constant about 100 μs at 290 K and about 200 μs at low temperature. Analogous luminescence was obtained in reduced sodium germanate glasses. No luminescence was observed in oxidized glasses…
Multiplet coupling and band structure in L2,3-edge XAS through multi-channel multiple scattering theory.
2009
International audience; Using the recently developed multi-channel multiple scattering (MCMS) method we have calculated the x-ray absorption spectra (XAS) at the L2,3-edge of transition metal compounds. The MCMS method is an ab initio scheme which combines an accurate description of the band structure of the material with a correlated many-electron wave function on the absorber atom. Thereby configuration interaction in the XAS final state, in particular multiplet effects, can be taken into account. In the present implementation, we use an electron-hole wave function and treat the interaction with all other electrons on a mean-field level. The calculated spectra agree well with experiment f…
Fabrication and Modelling of Three-Dimensional Sub-kelvin Phononic Crystals
2012
We have investigated the fabrication and computational modelling of threedimensional phononic crystals for the observation of full band gaps for thermal phonons at sub-kelvin temperatures. Self-assembled arrays of monodisperse polystyrene nanospheres have been fabricated using a vertical deposition technique. Optimal conditions for increasing crystal domain size and crystalline quality have been studied. In addition, the phononic band structure has been computed using the finite element method for the simple cubic lattice. The dependence of band structure on contact area between spheres has also been studied. For small enough contact area a large band gap is observed, predicting a strong in…
Pd–Pt alloys: correlation between electronic structure and hydrogenation properties
2001
Abstract Palladium and its alloys have been extensively studied because of their faculty to store reversibly hydrogen isotopes. Here, the substitution of palladium with platinum is investigated. Thermodynamical studies have shown an anomalous behaviour regarding to the classical models. This original behaviour is explained by the study of the electronic structure of the binary solid solutions. The drastic decrease of the hydrogen solubility in the Pd–Pt alloys is accounted for by the filling up of the palladium conduction band by the valence electrons of platinum. The anomalous decrease of the stability of the hydride is explained by the large broadening of the valence band due to the subst…
Application of 61Ni Mössbauer spectroscopy to chemical problems
1996
Using the possibility to produce 61Co sources at the MAinz MIcrotron, 61Ni Mossbauer spectroscopy was applied to different kinds of chemical problems. Measurements of isomer shifts and V zz values in some common compounds and compounds with unusual chemical bonding for comparison with band structure calculations, measurement of 61Ni Mossbauer parameters in model compounds for hydrogenase and dehydrogenase with an active [NiS4] centre, and study of novel binary NiF3 compounds at helium temperature are presented.
LDA+Uand tight-binding electronic structure of InN nanowires
2013
In this paper we employ a combined ab initio and tight-binding approach to obtain the electronic and optical properties of hydrogenated Indium nitride InN nanowires. We first discuss InN band structure for the wurtzite structure calculated at the LDA+U level and use this information to extract the parameters needed for an empirical tight-binging implementation. These parameters are then employed to calculate the electronic and optical properties of InN nanowires in a diameter range that would not be affordable by ab initio techniques. The reliability of the large nanowires results is assessed by explicitly comparing the electronic structure of a small diameter wire studied both at LDA+U and…
Modulated Crystal Structure and Electronic Properties of Semiconductor Cu47Si91P144
2000
Crystals of the copper silicon phosphide were synthesized by the iodine gas transport technique. The x-ray single crystal methods revealed a big superstructure with the lattice parameters a = b = 44.510 and c = 20.772 A and a basic tetragonal substructure with a = 3.7092 and c = 5.1930 A. Analysis of the intensities showed that the superstructure has a 1/2,1/2,1/2 tetragonal substructure with a = 22.255 and c = 10.386 A. This 1/2,1/2,1/2 substructure (Cu47Si91P144) and the basic tetragonal structure (Cu0.71Si1.29P2) were solved by the direct methods and refined in the I4m2 space group. The phosphide is a semiconductor with a small energy gap of 0.0269(1) eV. The electrical properties are co…
Wannier90 as a community code: new features and applications
2019
Wannier90 is an open-source computer program for calculating maximally-localised Wannier functions (MLWFs) from a set of Bloch states. It is interfaced to many widely used electronic-structure codes thanks to its independence from the basis sets representing these Bloch states. In the past few years the development of Wannier90 has transitioned to a community-driven model; this has resulted in a number of new developments that have been recently released in Wannier90 v3.0. In this article we describe these new functionalities, that include the implementation of new features for wannierisation and disentanglement (symmetry-adapted Wannier functions, selectively-localised Wannier functions, s…
Conductive nanostructures of MMX chains
2010
Crystals of [Pt-2(n-pentylCS(2))(4)I] show a transition from semiconductor to metallic with the increase of the temperature (conductivity is 0.3-1.4 S.cm(-1) at room temperature) and a second metallic metallic transition at 330 K, inferred by electrical conductivity measurements. X-ray diffraction studies carried out at different temperatures (100, 298, and 350 K) confirm the presence of three different phases. The valence-ordering of these phases is analyzed using structural, magnetic, and electrical data. Density functional theory calculations allow a further analysis of the band structure derived for each phase. Nanostructures adsorbed on an insulating surface show electrical conductivit…
The Properties of Co2Cr1-xFexAl Heusler Compounds
2006
The classical concept of band structure tuning as used for semiconductors by partly replacing one atom by a chemical neighbor without altering the structure is applied examplarily to the half-metallic ferromagnetic Heusler compound Co 2 Cr 1 - x Fe x Al. Band structure calculations are presented for ordered and disordered compounds. We present experimental and theoretical results. The connection between specific site disorder and the band structure is shown explicitly with particular emphasis on the half-metallic properties. Experimentally observed deviations from the ideal Heusler structure and from the simple Slater-Pauling rule for the magnetization are discussed in close relation to the…