bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Properties and Energy Band Structure of Zn3P2and Cd3P2 Crystals
Authors: Sobolev V. V. , Syrbu N. N. 
Published: July 2007

AbstractEdge absorption, photoconductivity, and reflectivity spectra are investigated of Zn3P2 crystals in the range from 1 to 12.5 eV and reflectivity spectra of Cd3P2 crystals in the range from 1 to 12.5 eV. The Eg value of Zn3P2 has been experimentally determined at 293 and 77 OK. Its nature has been found to be due to direct transitions. Three peaks of exciton and interband character have been observed in the photoconductivity spectrum of Zn3P2 single crystals. Complex structures (about 12 peaks) have been observed in the reflectivity spectra of both compounds. Most of these structures may be accounted for in terms of the well‐known theoretical calculations of their bands. Several peaks have been observed in the most thoroughly studied spectrum of Zn3P2. These peaks cannot be explained by the theoretical band scheme and are probably caused by the peculiarities of the bands of real crystals of the Zn3P2 type, which have been lost in the well‐known theoretical model because of the accepted simplifications of the crystal lattice.
Optical Intraband Absorption in Disordered Systems in the Presence of Electron‐Phonon Interaction
Authors: Böttger H. , Bryksin V. V. 
Published: July 2007

AbstractUsing Kubo's formula the optical intraband absorption is studied in two models of disordered systems. The model A is characterized by some few types of atoms and by strong electron‐phonon interaction, the model B by a continuous distribution of atomic levels and by an arbitrary strength of the electron‐phonon interaction. The frequency and temperature dependences of the optical absorption are discussed for both models. For model A the dependence of absorption on the concentrations of the different types of atoms is also investigated.
The Magnetic Field of Pure Superconductors with Non‐Isolated Flux Lines at Arbitrary Temperature
Authors: Brandt E. H. 
Published: July 2007

AbstractThe magnetic field distribution of pure type‐II superconductors with small magnetization is derived from the non‐local version of Gorkov's theory. At zero temperature Delrieu's result is reproduced: at the vortex centre the field shows a cusp and exceeds the external field. The form factors have alternating sign and decrease only as K−3. At larger magnetization all form factors become positive. At T = 0, even close to Hc2, a gap function is expected deviating considerably from the Hc2‐solution. This means a pronounced narrowing of the vortex core at low temperatures.
Influence of Spatial Dispersion on the Transmission Spectra of CdS Single Crystals
Authors: Voigt J. 
Published: July 2007

AbstractTransmission spectra are measured on extremly thin CdS single crystals with high quality in the energy range of exciton transitions from 1.8 °K to room temperature. Analysing the characteristics of the exciton absorption lines such as lineshapes, halfwidths, and oscillator strenghts it is found that the line An=1, E ⊥ c shows at low temperatures some “anomalies”, which cannot be explained in a model with weak exciton‐photon coupling but are qualitatively well understandable in a polariton model with spatial dispersion. This is caused by the fact that at low temperatures the exciton‐photon interaction prevails over the exciton‐phonon interaction resulting in a weakly‐damped polariton.
Interaction of Interstitial Cu Atoms with One Another and with Substitutional Impurities in a F.C.C. Cu Lattice
Authors: Ivanov L. I. , Platov Yu. M. , Pletnev M. N. 
Published: July 2007

AbstractUsing the technique of lattice statics, the interaction energies are calculated for octahedral interstitials interacting with one another and with substitutional impurities in the f.c.c. Cu lattice. The existence of a sufficiently strong attractive energy between a pair of octahedral interstitials has been established. It is shown that the character of interaction between an interstitial and substitutional impurity trap depends to a considerable extent on the sign of the dilatation volume of the impurity. On the basis of the results obtained, the structure of lower‐order interstitial clusters is examined, formed from substitutional impurity atoms under the influence of irradiation.
Optical Absorption of Ferroelectrical Copper and Chromium Boracites
Authors: Nesterova N. N. , Pisarev R. V. , Andreeva G. T. 
Published: July 2007

AbstractOptical absorption spectra of ferroelectrical boracites Cr3B7O13Cl, Cu3B7O13Cl, Cu3B7O13Cl, Cu3B7O13Br, and also borate CuB2O4 were studied in the spectral range from 2000 to 30000 cm−1 in the temperature interval 77 to 450 °K. The interpretation of the spectra are given on the basis of the crystal field theory including tetragonal distortion of the local environment of 3d‐ions in the lattice. The temperature dependence of the oscillator strength of the absorption band and absorption coefficient at a fixed frequency were investigated around the temperature of the ferroelectric phase transition in the copper boracites. The results show that the absorption is very sensitive to the displacement of the ions in the crystal lattice at the phase transition. For CuCl boracite a change of the slope of the temperature dependence of the absorption near the fundamental absorption edge was observed.
Dispersion of Generalized Surface Phonon Polaritons on α‐Quartz Observed by Attenuated Total Reflection
Authors: Falge H. J. , Borstel G. , Otto A. 
Published: July 2007

AbstractReal and virtual excitation generalized surface polaritons are investigated on a 45° cut of an α‐quartz crystal. For the wave vector of the surface polariton coplanar with the normal to the surface and the optical axis they are transverse magnetic polarized extra‐ordinary waves. The experimental results agree with calculated dispersion curves. By attenuated total reflection for transverse magnetic polarized radiation it is shown that virtual excitation generalized surface polaritons exist only for certain ranges of the angle between the surface and the optical axis.
Application of the Random‐Element Isodisplacement Model to Long‐Wavelength Optical Phonons in CdSexTe1−x Mixed Crystals
Authors: Górska M. , Nazarewicz W. 
Published: July 2007

AbstractInfrared reflection spectra from mixed crystals CdSexTe1–x (0 ≦ x ≦ 1) have been investigated in the spectral region from 90 to 300 cm−1 at room temperature. The spectra contain two distinct reststrahlen bands whose strengths and frequencies depend on the composition, x. Using Kramers‐Kronig analysis the frequencies of long wavelength optical phonons were obtained. It is established, that the dependence of the phonon frequencies on the composition of crystals does not show any discontinuity when changing the structure of the mixture from zincblende to wurtzite. The calculations, based on the random‐element isodisplacement (REI) model, of the dependence of long‐wavelength optical phonon frequencies on the composition x are in good agreement with the experimental results.
Electron Energy Loss Measurements on Fluorene (C13H10) Vapour and Single Crystals
Authors: Venghaus H. , Hinz H.‐J. 
Published: July 2007

AbstractElectron energy loss spectra from 0 to 40 eV were measured with 55 keV electrons on fluorene single crystals. The momentum transferred to the crystal by the electrons scattered inelastically was taken to be parallel to the main axes of the dielectric tensor ε(E). The energy loss functions Im (−1/εii) (i = x, y, z) were derived from the spectra and the tensor elements εii(E) calculated from Im (−1/εii) by Kramers‐Kronig analysis. The results obtained are discussed in terms of excited molecular states determined by electron energy loss measurements on fluorene vapour in the present investigation. The results are also related to optical absorption measurements performed by other authors on fluorene in solution.
The Local and Quasi‐Local Impurity States in the Finite One‐Dimensional Hubbard Model
Authors: Mikhailov I. D. , Shelestina I. Yu. 
Published: July 2007

AbstractAn analytic expression for the Green's function of the ground state of the finite one‐dimensional Hubbard model and the density of the electronic states on the sites are obtained. It is shown that the introduction of a local perturbation can cause the formation of quasilocalized levels which may transform into localized states when the pertubation reaches some critical value.
Quantum‐Efficiency of Multiphonon Transitions According to the Static Coupling Scheme
Authors: Pässler R. 
Published: July 2007

AbstractOn the basis of the static coupling scheme a standard expression for the quantum‐efficiency of multiphonon transitions of an electronic system interacting with the quantized normal oscillation modes of the crystal lattice is given. For the case of band–imperfection transitions both in homopolar and heteropolar semiconductors, the quantum‐efficiency reduces to a simple function of three imperfection parameters to be determined from luminescence spectra data and the temperature. In order that imperfections with a level near the middle of the band gap in typical crystal phosphors may act as killer centres at room temperature, the associated deformation energies of the lattice must exceed an amount of about 11 to 17% of the width of the gap.
Elastic Electron Scattering in Symmetry‐Induced Zero‐Gap Semiconductors
Authors: Szymańska W. , Bogusławski P. , Zawadzki W. 
Published: July 2007

AbstractRelaxation times for elastic electron scattering in the symmetry‐induced zero‐gap semi‐conductors of zincblende structure are calculated, taking into account the nonparabolic character of the conduction band both in the density of states and the electron wave functions. The calculation is based on the band structure proposed by Groves and Paul and uses exact k · p solutions for the three‐level model of Γ8, Γ6, and Γ7 levels. Electron scattering by charged impurities and heavy holes, optical phonons (screened polar interaction) and acoustic phonons is considered. Spin‐flip transitions play an important role for all scattering modes. An anomalous q‐dependence of the static dielectric function due to low energy excitations between the Γ8 heavy hole and conduction bands is shown to have small effect on the ionized impurity scattering at low temperatures. It is demonstrated that transverse modes give a large contribution to acoustic scattering. In all cases the Γ8 symmetry of the band‐edge and the nonparabolicity of the band at higher energies have essential effect on the scattering processes.
Spin–Lattice Coefficients of Gd3+ in CdF2
Authors: Falkowski K. , Szumowski J. , Krukowska‐Fulde B. , Jabloński R. 
Published: July 2007

AbstractEPB spectra of Gd3+ in CdF2 under uniaxial stress were observed and the spin–lattice coefficients of second and fourth order were measured. The measurements were performed in X band in the temperature range 77 to 300 K. Experimental data show that the fourth order term gives an important contribution to the shift of the fine structure resonance lines. Comparison with the results of other authors at different frequencies does not reveal a frequency dependence. Also a temperature dependence of the spin–lattice coefficients is not found. From the value of the coefficient Clg responsible for the symmetric deformation it is deduced that the temperature changes of B are due to thermal expansion.
The Quasi‐Molecular Large Unit Cell Model in the Theory of Deep Levels in Imperfect Crystals: Point Defects in Graphitic Boron Nitride
Authors: Dobrotvorskii A. M. , Evaeestov E. A. 
Published: July 2007

AbstractThe possibilities of the quasimolecular “large unit cell” approach in the theory of deep energy levels in imperfect solids are discussed and some general principles of its realization are formulated. The success of this approach is illustrated by the application to the defect level problem in graphitic boron nitride (vacancies and impurity carbon atoms at boron and nitrogen lattice sites are considered). The results obtained are compared with available experimental data, and possible defect models are discussed.
On the Theory of Conductivity in Disordered Semiconductors
Authors: Keiper E. , Kleinert P. 
Published: July 2007

AbstractKubo's general formula for calculating the conductivity is studied for the case, where the electron–electron interaction is taken into account in disordered semiconductors. The configuration averaged Green's functions occurring in this connection satisfy equations of motion which are strongly modified in comparison with the well‐known expressions for crystalline materials.
The X‐Ray K Emission Band of Magnesium from Mg(OH)2 Single Crystals
Authors: Freund F. 
Published: July 2007

AbstractThe MgKß emission band has been measured of Mg(OH)2 single crystals. The MgKP band shows two maxima at 1297 and 1292 eV having an intensity ratio of about 2: 1. They are assigned to 3Tlu → 1s and 2Tlu → 1s transitions involving the lπ and 3σ molecular orbitals of the OH− ligands, respectively. The assignment is based on octahedral symmetry oh, even though the [Mg(OH)2]‐polyhedra in Mg(OH)2 have trigonal symmetry, D3d. The results are compared with known data from MgO and with recent MO‐LCAO calculations.
Lattice Dynamics and Anharmonic Effects in AgCl
Authors: Fischer K. 
Published: July 2007

AbstractThe lattice vibrations of AgCl are calculated from an extended shell model where the shell of the Ag‐ion has a quadrupolar and a rotational degree of freedom. The model parameters are discussed in connection with the electronic 4d‐shell of the Ag‐ion. Thermal expansion, infrared reflection, and anharmonic frequency shift are calculated from a simple extension of the harmonic model, and are found to be in good agreement with experimental data. The anharmonic effects are comparable to those of the alkali halides.
A Shell Model for Molecular Crystals
Authors: Luty T. , Pawley G. S. 
Published: July 2007

AbstractThe rigid molecule approximation for the lattice dynamics of molecular crystals is not good when there is considerable molecular polarisability. A shell model is presented which takes account of the polarisability, and this may be called the rigid shell model. The relative arrangements of the cores throughout a molecule is rigid, and the relative arrangement of the shells is also rigid, but the shell array is free to move with respect to the core array. Each shell is related to its core by an identical isotropic force constant. In the course of lattice vibrations small dipole moments are generated at the atomic sites, and the interaction between these dipoles needs to be calculated. This is done explicitly between the dipoles within neighbouring molecules, but for the more distant neighbours it is assumed that only the dipole moment summed over the whole molecule is important, and the interaction between these is done using Ewald's transformation. The short range repulsive forces and the medium range Van der Waals attractive forces are included by using a 6‐exp atom‐atom potential function.
Elastic Interaction between Atomic Defects
Authors: Kronmüller H. , Schaefer H.‐E. 
Published: July 2007

AbstractThe elastic interaction between defects of orthorhombic symmetry is considered. Explicit results for the elastic stress tensor are derived for defects with finite extensions assuming a Gaussian distribution of the quasiplastic deformations. Within the framework of the dipole approximation it is shown that 〈110〉‐crowdions form bound pairs at small separation whereas their interaction may be reptilsive or attractive at large separation.
Exciton–Phonon Interaction in Crystals of Linear Polyacenes
Authors: Kurik M. V. , Tsikora L. I. 
Published: July 2007

AbstractInvestigation results of the exciton absorption band shape, its long‐wavelength edge, and maximum position and half width as a function of temperature are systematized for linear polyacene crystals from naphthalene to pentacene. It is found that excitons interact mainly with optical phonons resulting in a broadening and shift of the exciton absorption band. The shape of the absorption bands is found to be complicated and may be described by the Voigt function. Some assumptions on the character of the exciton–phonon interaction are made.
Mean Spherical Model and Structure Factor of Liquid Mercury and Aluminium
Authors: Rao R. V. Gopala , Murthy A. K. K. 
Published: July 2007

AbstractA closed form expression for S(k), the structure factor, has been derived, taking the square well potential as a perturbation in the mean spherical model approximation. This expression has been used to calculate the structure factor and radial distribution function, g(r), for liquid mercury and aluminium at various temperatures and densities. The very good agreement between theory and experiments suggests that the representation of the attractive tail by a square well potential is a satisfactory one and the concept of pairwise interactions is a useful tool in understanding some of the structural problems of liquid metals.
Linear Magnetic Birefringence and Near Infrared Absorption of K2NiF4
Authors: Kleemann W. , Pommier J. 
Published: July 2007

AbstractEvidence of 2D magnetic short‐range order has been observed in the linear magnetic birefringence (LMB) of K2NiF4 up to 3TN (≈︁300 K) in agreement with specific heat and Raman data. Below TN/2 the LMB is proportional to the long‐range order parameter M2 Both results are explained by magnetostriction due to 2D and 3D Spin–order, respectively. The fine structure of the 3A2g → 3T2g absorption band at LHeT is discussed. The MCD of the lowest Spin–orbit component τ3 yields g ‖ = 2.27 ± 0.04 for the ground state. The Debye temperature θ ≈︁ 335 K is obtained from the temperature dependence of the τ3 line. Only about 5% of the thermal line shift below 0.7 TN is estimated to be due to the decrease of the exchange stabilization of the ground state.
Dislocations and line charges in anisotropic piezoelectric insulators
Authors: Barnett D. M. , Lothe J. 
Published: July 2007

AbstractThe six‐dimensional framework developed by Stroll to treat dislocations and line forces in classical anisotropic elastic media is extended to an eight‐dimensional formalism to treat dislocated piezoelectric insulators. The solutions are recast into a four‐dimensional form using the so‐called integral formalism developed previously by the authors. This technique allows one to compute the gradients of the mechanical displacement and the electrostatic potential as well as the total energy of the dislocated piezoelectric by merely computing three constant real (4 × 4) matrices using numerical integration, numerically a considerably simpler method than the prescription attached to the original Stroh formalism.
Polarons and effective electron‐hole interaction in anisotropic polar crystals
Authors: Fock H. , Kramer B. , Büttner H. 
Published: July 2007

AbstractStarting from the Fröhlich electron‐phonon interaction for crystals with anisotropic band masses and dielectric constants, the polaron self‐energy and effective mass are calculated. An expression for the effective electron‐hole interaction in anisotropic crystals is derived. The effect of the electron–phonon interaction on the anisotropy of the electron–hole potential is discussed.
Structure of the infrared absorption bands and the phonon sidebands of SH‐impurity molecules in potassium halide crystals
Authors: Mauring T. , Rebane K. 
Published: July 2007

AbstractThe structure of the SH− stretching hand and its phonon sidebands in KCl, KBr, and KI crystals from 2 to 300 K has been studied. A splitting of the stretching bands was observed at low temperatures into three or more components that may be attributed to the formation of the SH− clusters. The intensity distribution of the sidebands corresponds, in general, to the phonon density of states of the pure host lattice. A local gap mode was observed in the phonon spectrum gap region at the frequencies 95 and 78 cm−1 in KBr and KI, respectively. The sharp maxima at 136 cm−1 in KI and at 158 cm−1 in KBr, which are situated in the lattice vibration region, were related with the pseudolocal modes.
The lattice distortion around a vacancy in F.C.C. metals
Authors: Miller K. M. , Heald P. T. 
Published: July 2007

AbstractThe lattice distortion produced by an isolated vacancy in aluminium and the noble metals has been calculated using a discrete lattice model which assumes non‐equilibrium pairwise interactions extending out to second nearest neighbours. It is shown that, to first order, the relaxation volume associated with a vacancy can be expressed in terms of the elastic constants. For aluminium the asymptotic displacement field calculated from the lattice model is compared with the corresponding elasticity results.
Theory of inter‐valence‐band electronic raman scattering in cubic semiconductors without and with an external electric field
Authors: Bechstedt F. , Enderlein R. , Peukere K. 
Published: July 2007

AbstractInterband electronic resonance Raman scattering for excitation from the split‐off valence band to the light‐hole and heavy‐hole band and from the light‐hole band to the heavy‐hole band in p‐type semiconductors with diamond or zincblende structure has been studied. The polarization dependence of these electronic Raman transitions is stated. The influence of a strong electric field on the form and magnitude of the scattering cross section is calculated. The Raman spectrum will be depressed in the presence of the strong electric field. All explicit results are given for band parameters of Ge.
The translational symmetry in the molecular models of solids
Authors: Evarestov R. A. , Petrashen M. I. , Ledovskapa E. M. 
Published: July 2007

AbstractIt is shown that the translational symmetry of a solid when the molecular models are applied, can be taken into account in the framework of the “large unit cell (LUC)” approach. The method of choosing of LUC, suitable for a calculation of the energy levels and one‐electron wave functions corresponding to some given values of the wave vector is given. The way of connecting the molecular orbitals obtained in the LUC calculation with the one‐electron states of the infinite crystal is discussed.
Schottky‐type anomaly in the linear optical birefringence of DyPO4
Authors: Jahn I. R. , Smith S. H. 
Published: July 2007

AbstractThe linear optical birefringence of DyPO4 shows anomalous temperature behaviour between 10 and 150 K. The effect is considered to be due to the excitation of a higher crystal field component of the 6H15/2 ground state of Dy3+. From this the separation between the lowest and the first excited state is determined as Δ/k = (97 ± 3.5) K.
Studies on substitutional defects in alkali halide crystals
Authors: Paul S. , Sengueta S. 
Published: July 2007

AbstractA simple model is developed for the study of substitutional defects. Region I consists of nearest neighbours to the defect site. In region II, the relaxation is taken ∼1/r2 and the constant is determined from the equilibrium condition. Using harmonic approximation an extremely simple expression for the heat of formation is obtained. Values of heat of formation obtained from this expression show good agreement with experiment and with those obtained from more sophisticated models.
Thermomagnetic effects in tin‐doped bismuth
Authors: Uher C. , Goldsmid H. J. , Drabble J. R. 
Published: July 2007

AbstractSeveral of the thermo‐galvanomagnetic phenomena have been studied for bismuth doped with about 0.24 at % Sn in the temperature range from about 5 to 300 K. The Hall coefficient, magneto‐resistance, Seebeck coefficient, Nernst coefficient, and thermal conductivity have been measured in magnetic fields of up to about 6 T with current flow in the trigonal and bisectrix directions. The most remarkable observation has been that of a negative Seebeck coefficient for a range of temperatures well below that at which electrons in the main conduction band should be excited. A group of electrons, possibly closely associated with the light hole band, is invoked t o explain the results.