The symmetry properties of the energy bands of α- and β-quartz

The character tables, compatibility relations and dipole selection rules are given for all points of the Brillouin zones of the studied space groups taking spin into consideration. Special attention is devoted to the effects of time reversal.     

The symmetry properties of the energy bands of α- and β-quartz

The qualitative features of the band spectra of - and -quartz are derived both from the group-theoretical results tabulated in paper I and from a comparison of the spectra of both modifications (which change into each other by a phase transition of the second kind). It is also shown that the same energy values in the Brillouin zone correspond to the enantiomorphous space groups. The Appendix sums up some specific questions concerning the band structures of crystals with low point symmetry: the fundamental region of the Brillouin zone, the anisotropy of selection rules, the effects of time reversal, a comparison with the band structure of a substance having higher symmetry.The author expresses his gratitude to A. Fingerland and B. Velický for stimulating discussions.     

High energy x-ray satellites ofL 2,3 emission bands of Na,Mg, Al,and Si

The x-ray satellites found on the high energy sides of theL _2,3 emission bands of Na, Mg, Al, and Si have previously been attributed to the radiative decay of double ionization states. However, in some recent papers it has been proposed that the satellites in Al and Si may arise from the simultaneous radiative decay of a core ionization state and a volume plasmon. A detailed investigation of the high energy satellites of theL _2,3 x-ray emission bands of Na, Mg, Al, and Si have been made for incident electron energies from 500 eV to 5 keV and the results compared with the double ionization theory. Plasmon involvement is also considered. The present results lend additional support to the first interpretation; namely, that the satellites arise from the radiative decay of atoms with a double vacancy in theL _2,3 (2p) shell and not from the plasma phenomenon.     

The influence of shear bands on final structure and magnetic properties of 3% Si non-oriented silicon steel

The presence of shear bands in the deformed material before final annealing is very important for Goss and Cube textures formation in silicon steel [S.C. Paolinelli, M.A. Cunha, J. Magn. Magn. Mater. 255 (2003) pp. 379. [1]; J.T. Park, J.A. Szpunar, Acta Mater., 51 (2003) 3037. [2]]. The increase of the hot-band grain size can increase the number of shear bands, which favor the nucleation of these orientations. In this work, the effect of the hot band grain size variation, promoted by varying the hot rolling finishing temperature, on final structure and magnetic properties was investigated for 3% Si alloy. It was found that the increase of the hot-band grain size increases the occurrence of shear bands and promotes an increase of η fiber fraction and a reduction of γ fiber fraction, improving the magnetic induction. On the other hand, the final grain size is reduced when the hot-band grain size is larger than 190 μm, deteriorating the core loss values in spite of the texture benefits. The reduction of final grain size was explained by the increase of the number of nuclei at the beginning of the recrystallization caused by the increase of shear bands in the deformed material.     

Electron energy bands in semiconductor films

The possible nature of the band structure in crystal films is examined on the basis of a consideration of the symmetry possessed by their structure.For germanium and silicon of the p- and n-types with various different orientations of the film the connection is found between the band structures of the film and of the bulk crystal. The result is obtained that with the orientation [111] an n-germanium film, like an n-silicon film with the same orientation must have a single-trough minimum.     

High energy final bands in Cu

We probe final energy bands of Cu in the kinetic energy range 20 eV ? E ?120 eV by angle resolved photoemission techniques. We observe deviations from free electron like behaviour in agreement with a LEED-type KKR calculation (Jepsen [5]). The lifetime broadening of the final bands at 60 eV kinetic energy is ～5 eV (FWHM).     

Influence of thermomechanical processing on shear bands formation and magnetic properties of a 3% Si non-oriented electrical steel

The effect of thermomechanical processing on the formation of shear bands and on the magnetic properties of a 3.0 wt% silicon non-oriented steel was investigated by hot rolling samples with different thicknesses at different temperatures, in order to obtain a variation in hot band grain size and cold strain. All the samples were processed in a single-stage cold rolling and finally annealed at 1020 °C. It was found that the increase of the hot band grain size decreases the γ fiber volume fraction and increases the η fiber volume fraction after the final annealing. The increase of the cold strain strongly contributed to this result. A good combination of intense generation of shear bands, and proper crystallographic texture, due to higher nucleation of grains with favorable orientations to magnetization in these bands, can be obtained for the samples hot rolled at 1000 and 1120 °C and submitted to cold strain of 64.3% and 72.2% respectively. However the best combination of B₅₀, W_15/60 and μ_r can be obtained by hot rolling the samples at 1000 °C to the thickness of 1.4 mm, corresponding to 64.3% of cold strain.     

The absolute positions of calculated energy bands

The absolute positions of calculated crystalline energy bands depend upon the choice of charge cluster used to generate the total crystalline charge for the coulomb potential calculation. The coulomb potential (and hence the bands) will be shifted from the Ewald limit by 2π times the trace of the second moment tensor of the charge cluster divided by three times the volume of the unit cell. Energy bands obtained from different calculational models can thus all be corrected to the same Ewald limit. Energy bands can also be aligned more realistically with those in a finite crystal by calculating the shift in the bands from the Ewald limit due to a free atom or ion surface charge density.     

Third neighbor linear-combination-of-atomic-orbitals energy bands of zincblende

It is shown that inclusion of third nearest neighbor interactions and omission of the usual two center approximation in the simplified Slater-Koster LCAO method leads to an improved interpolation formula for the energy bands of wide bandgap partially ionic II–IV compounds such as zinc sulfide.     

Measurement of the interfacial energy between amorphous Si and crystalline Si

The experimental data of crystallization of amorphous Si thin films on single crystal Si substrates and on inert substrates have been analysed by a kinetic model of phase transformation. On the basis of the analysis, the interfacial energy between amorphous Si and crystalline Si has been calculated to be about 0.30 eV/atom and the number of Si atoms in the critical nucleus to be about 110.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

On the nature of energy bands in tetracyanoplatinates

Optical data and band calculations are presented for a series of tetracyanoplatinates with varying Pt—Pt-distance R. The band gap energies decrease according to R^-3 with decreasing R. The energy bands which determine the optical and electrical properties for E6 c originate from (Pt5d_z², 6s) and (Pt6p_z, CNπ¹) hybrid molecular states.     

Conduction bands and invariant energy gaps in alkali bromides

Electronic structure calculations of the alkali bromides LiBr, NaBr, KBr, RbBr and CsBr are reported. It is shown that the conduction band has primarily bromine character. The size of the band gaps of bromides and alkali halides in general is reinterpreted. Received: 26 January 1998 / Revised: 16 March 1998 / Accepted: 23 March 1998     

Phenomenological electronic energy bands in graphite intercalation compounds

The electronic energy bands near the Fermi level for both donor and acceptor graphite intercalation compounds are modelled using a k_z-axis zone folded form of the SWMcC bands for pristine graphite. The effect of intercalation is included through terms for the intercalant and for the interaction between intercalant and graphite layers. Graphitic π-bands appropriate to both donor and acceptor compounds are presented.