bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of self‐trapped exciton recombination in CsI
Authors: Lamatsch H. , Rossel J. , Saurer E.
Published: July 2007

The yield and decay lam of the intrinsic luminescence of CsI are studied. From the results obtained a configuration coordinate scheme for the relaxed exciton is suggested and the nature of the relaxed state is specified. The kinetics of electron‐hole recombination following an ionizing irradiation is reported.
Lifetimes of bound excitons in InP
Authors: Heim U.
Published: July 2007

The decay times of two bound exciton emission lines in InP have been measured at very low excitation levels and found to be of the order of 0.5 and 1.5 ns. These times agree within a factor of two with theoretical values, which were estimated using the model of Rashba and Gurgenishvili. The oscillator strength per molccule of the free exciton has been evaluated and found to be 8 × 10−5 The bound exciton oscillator strengths are larger by five orders of magnitude.
Exciton binding energies of layer‐type semiconductors GaSe and GaTe
Authors: Grandolfo M. , Gratton E. , Somma F. Anfosso , Vecchia P.
Published: July 2007

New experimental results are given on the absorption coefficient of GaSe and GaTe single crystals near the fundamental edge. A new analysis of the direct exciton region due to Sell and Lawaetz has been used to assign the energy position of the exciton levels and of the energy gaps, and to determine the exciton binding energies.
Electronic and nuclear stopping cross sections in carbon for light mass ions of 4.5 to 46 keV energy
Authors: Höberg G.
Published: July 2007

The mean stopping cross section, S, of thin carbon foils has been determined for light mass particles with 3 ≦ Z1, ≦ 18. The dependence of stopping cross section on foil thickness and scattering angle is reported. The energy of the incident ions ranged from 4.5 to 46 ke V. The electronic, Se, and nuclear, Sn, stopping cross sections were deduced from the experimentally determined mean stopping cross section at zero output angle, \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {S(0)} \, = \,S_e \, + \,\overline {S_n \,(0)} $\end{document}, by putting \documentclass{article}\pagestyle{empty}\begin{document}$ S_e \, = \,\mathop {\lim}\limits_{t \to 0} \,\overline {S(0,\,t)} $\end{document} where t is the foil thickness. The reported values of Se, are in t → 0 good agreement with previously published results. The mean nuclear stopping cross section in the forward direction is found to reach a saturation value in foils thicker than about 8 μg/cm2. The increase of S with scattering angle is parabolic at small scattering angles and linear at large scattering angles.
Stress‐induced splitting of excitons due to exchange interaction in zinc telluride
Authors: Wardzyński W. , Giriat W. , Szymczak H. , Kowalczyk R.
Published: July 2007

The effect of uniaxial stress on the exciton reflection spectrum at 77 °K of ZnTe was studied by the wavelength modulation technique. The observed splitting is explained taking into account the exchange interaction between the spins of the electron and the hole composing the excition. From comparison of the experiment and the appropriate theory it is concluded that in ZnTe at 77 °K the second‐order term of exchange interaction being linear in strain and describing the variation of exchange interaction with stress plays the main role.
Magnetic dilution effects on morin phase transition in hematite
Authors: Srivastava J. K. , Sharma R. P.
Published: July 2007

Mössbauer investigations, in the range 10 to 1000 °K, in (1−x) Fe2O3‐x Al2O3 systems, have shown a nonlinear rapid decrease of the Morin temperature, TM, with the increasing magnetic dilution of the α‐Fe2O3 lattice. The phase transition is not sharp and becomes more and more diffused as the magnetic dilution increases. An anomalous variation of the angle, θ, between the spin direction and the c‐axis is seen for the 5.27 wt% diluted sample indicating the presence of three magnetic phases in this case. Unlike the case of undiluted α‐Fe2O3, for the 0.56 wt% diluted sample at low temperatures, outside the phase transition region, the Fe3+ spins do not lie along the c‐axis but are canted at an angle of about 30°. This angle, θ ≈ 30°, does not seem to change much with further increase in dilution. It is also seen that with dilution, the ratio TM/TN and the anisotropy energy, K, deduced from the temperature and concentration dependence of the hyperfine field, are decreased (TN Néel temperature). This supports the existing anisotropy theory.
High field transport in semiconductors. The drifted Maxwellian approach. I. general theory
Authors: Stokoe T. Y. , Cornwell J. F.
Published: July 2007

The rates of loss of energy and momentum by electrons to the polar optical, acoustic, and ionised impurity scattering mechanisms are calculated. They are averaged exactly over the drifted Maxwellian distribution function, from which the high field transport characteristics of semiconductors can be calculated. The formulae are expressed in terms of a generalised band structure, and the effect of the mixing of Bloch states with spin‐reversal scattering is included.
Structure factor and atomic distribution in liquid metals by X‐ray diffraction
Authors: Waseda Y. , Suzuki K.
Published: July 2007

X‐ray diffraction patterns have been obtained from liquid metals (Al, Ga, In, Tl, Pb, Sn, Bi) near the melting point. After calculating the structure factor (Fourier analysis), the atomic radial distribution function was evaluated from which interatomic distance and coordination number were obtained. It has been shown that the ratio (K2/K1) of the position of the first peak (K1) to that of the second peak (K2) in the structure factor is a very useful parameter to represent the structure of liquid metals.
Charged particle energy loss to electron gas
Authors: Pathak A. P. , Yussouff M.
Published: July 2007

The contribution of the conduction electrons to the stopping power (– dE/dx) of fast charged particles in a crystal has been calculated using different forms of the dielectric function. The various approximate forms of dielectic functions used are: 1. random phase approximation (RPA), 2. Hubbard approximation (both, screened and unscreened), 3. Kleinman approximation, and 4. the dielectric function obtained by variational calculation of Langreth. The intermediate velocity range for the incident particles, namely 2 VF<V<10 VF was investigated and it has been found that in this region the stopping power varies inversely to the particle velocity. Moreover the velocity dependence is found to be insensitive to the form of the dielectric function used in the calculation.
The effects of sample imperfections on optical spectra
Authors: Filiński I.
Published: July 2007

The results of the theory of light reflection from rough surfaces have been extended to cover the case of light transmission through a sample with rough surfaces, as well as reflection and transmission for inhomogeneous samples. A concept of “Inhomogeneity Induced Roughness” of the constant phase plane has been introduced to describe the specular reflection from inhomogeneous media. The drastic influence of the multiple scattering effect on the optical spectra has been demonstrated for a simple model. The generalized formulae for reflection and transmission of light for imperfect samples are given. Finally, several peculiar experimental observations concerning exciton spectra in II–VI compounds, light scattering at the plasma frequency in metals, electroreflection, and other effects are discussed.
Perturbation theory in transmission electron diffraction I. The perturbing matrix is constant and hermitian
Authors: Serneels R. , Gevers R.
Published: July 2007

Instead of using the usual Schrodinger equation perturbation theory is directly applied to the system of Howie and Whelan. According to the nature of the perturbing dynamical matrix generally three different types of perturbation are distinguished. The perturbing dynamical matrix may be a) constant and hermitian, b) constant but not hermitian, c) not constant but depth dependent. The perturbing dynamical matrix is supposed to be constant and hermitian. Applying perturbation theory series expmsions for the eigenvalues and eigenvectors of the dynamical matrix are derived. Furthermore these series expansions are used to obtain series expansions for the amplitudes and intensities of the different beams. Two practical examples are discussed. First the influence of weak beams is studied by this method. As a particular result the kinematical expression for the amplitude of the weak beam formed by scattering out of N + 1 strong beams is given. Secondly it is suggested that the method can be applied to study the influence of slightly tilting the crystal around an orientation for which the problem was solved.
Optical phonon drag effect in single crystals of CdSe
Authors: Kubalkovl S. , Sakalas A.
Published: July 2007

An investigation is made of the optical phonon drag effect. In contrast to [1] where all calculations were performed for low carrier densities and the change of sign of phonon drag effect at low temperatures was obtained, it is shown in this paper that for high carrier densities no change of sign takes place. The phonon drag effect is found to be inversely proportional to the carrier density. These conclusions were checked experimentally on CdSe single crystals.
Local approximations in the theory of hot electrons in spatially inhomogeneous systems
Authors: Zviagin I. P.
Published: July 2007

The distribution function of hot electrons in a static, slowly in space varying electric field is calculated. This distribution function is used to obtain a phenomenological expression for the current density. The transport coefficients are presented as local functions of the field strength, drift velocity, or power absorption. The connection of different local approximations is discussed.
Low temperature thermomagnetic effects in n‐type PbS
Authors: Chan Y. C. , Finlayson D. M.
Published: July 2007

Transverse and longitudinal Nernst effects have been measured over the temperature range 1 to 80°K. Acoustical and optical phonons are confirmed as the main scattering mechanisms at liquid air temperatures. At low temperatures neither ionised nor neutral impurity scattering provide an explanation of the measurements. The results are tentatively explained in terms of localised spin scattering.
Piezobirefringence in the vacuum ultraviolet: Alkali halides and alkaline‐earth fluorides
Authors: Sánchez C. , Cardona M.
Published: July 2007

The spectral dependence of the piezobirefringence coefficients of NaCl, KCl, LiF, CaF2, SrF2, and BaF2, at room temperature is measured. From these results values for the shear deformation potentials of the energy bands are obtained. The LiF data suggest that the lowest interband edge occurs along [lll], a situation unique among the alkali halides. The data for the alkaline‐earth fluorides indicate a rather complicated structure for the lowest absorption edge.
On the asymptotic linear dependence of orthogonalized plane waves
Authors: Dyakin V. V. , Reser B. I. , Shirokovskii V. P.
Published: July 2007

The influence of the linear dependence of orthogonalized plane waves on energy band calculations is investigated. One of the modifications of the method is analysed. Calculations for diamond illustrate the general considerations.
The mechanical interaction of a point defect with a surface layer
Authors: Bacon D. J.
Published: July 2007

A relationship is derived which expresses the interaction energy between a source of internal stress and a surface in terms of the elastic field. This is used to consider the mechanical interaction energy between a point defect and a layer of finite thickness on the surface of body. For convenience, the body is taken to be semi‐infinite and isotropic, and the layer is also isotropic but with different elastic constants. The point defect is approximated by a dilatation centre. A transform method is used to obtain the elastic field, and this gives analytic expressions for the interaction energy in the limiting case corresponding to a bicrystal. For situations of finite layer thickness, the energy has been determined numerically for a wide range of values of elastic constants, layer thickness and defect to layer‐matrix interface distance. The conditions which give rise to attraction or repulsion of the defect from the interface have been studied, not only for the case in which the defect is in the matrix but also when it is in the layer.
The low temperature magnetic susceptibility of semiconductors in strong magnetic fields
Authors: Wallace P. R. , Gupta O. P.
Published: July 2007

We calculate the magnetic susceptibility of Kane‐type semiconductors in the ultra‐quantum limit, taking account of spin splitting. It is shown that, when the bottom of the upper spin branch of the n = 0 Landau band passes through the Fermi surface, there is a strong minimum in the diamagnetic susceptibility as the spins of all free carriers align. The conditions are considered for transition to a conduction electron paramagnetism. Calculations are carried out for InSb with carrier concentrations of 2 × 1016 and 2 × 1017 cm−3.
No‐phonon and phonon‐assisted exciton absorption in GaAs1 − x, Px with indirect energy gap
Authors: Pikhtin A. N. , Razbegaev V. N. , Yaskov D. A.
Published: July 2007

Investigating the fine structure of intrinsic absorption of GaAs1 − x, Px at 4.2°K, the influence of composition x and band structure on the no‐phonon and phonon‐assisted processes of light absorption by excitons has been determined.
The modified convolution approximation model for neutron scattering from short range ordered paramagnets
Authors: Rao L. Madhav
Published: July 2007

A modified convolution approximation model is developed to explain neutron scattering from short range ordered paramagnets, employing the concepts used in understanding neutron scattering of simple liquids. Calculations based on this model are compared with the following experimental results in paramagnetic MnO: (1) scattered neutron energy spectra at room temperature, using the triple‐axis spectrometer, (2) scattered neutron time‐of‐flight spectra at 124, 143, and 298 °K. The model explains satisfactorily the narrowing of the line shape observed in (1) and also explains qualitatively the observed energy shifts in (2), at all the three temperatures without assuming spin‐wave like excitations. These apparent energy shifts are explained to arise essentially from the “non‐constant Q” nature of the measurements.
On the many‐beam dynamical theory of electron diffraction in faulted crystals
Authors: Schapink F. W.
Published: July 2007

The dynamical theory of electron diffraction in a thin foil with a stacking fault is reconsidered from the point of view of Bloch wave scattering at the stacking fault. A formalism for many‐beam systematic diffraction is developed from which a close relationship between the stacking‐fault‐induced transformation of the various Bloch waves and the corresponding transformation of the excitation amplitudes of the Bloch waves emerges. It is suggested that the present formulation shows more clearly the nature of the scattering process involved.
Luminescence due to trapping of holes by In+ and In+v centres in KCl:In
Authors: Zazubovich S.
Published: July 2007

The trapping of holes by In+ and In+v centres in KCl:In is found to be accompanied by luminescence of the same spectral composition as the emission spectra of In++ and In++v centres, respectively. The processes of migration and trapping are investigated for holes thermally or optically released from In++, Vk, VF and other hole centres.
Temperature Shift, Recoil‐Free Fraction, and Force Constant in Mössbauer Studies
Authors: Gupta G. P. , Lal K. C.
Published: July 2007

A simple relation connecting the temperature shift, the recoil‐free fraction, and the force constant has been derived. The force constants for host–host and for impurity–host atoms and their ratios have been calculated from this relation. The values thus obtained are compared with the values obtained by other authors. The agreement has been found to be satisfactory and confirms the applicability of the derived relation. The results also indicate the change in the force constant for an impurity atom in a host lattice.
Magneto‐Reflectance of the First Exciton in KI and RbI
Authors: Ahrenkiel R. K. , Teegarden K. J.
Published: July 2007

The Zeeman effect of the first exciton in KI and RbI has been measured by a technique which senses the magneto‐reflectance dichroism. The analysis indicates an excited‐state g‐factor of about 0.9. This result cannot be interpreted in terms of either a Wannier or Frenkel model.
Comparison of Lattice Parameter and Resistivity Change in Electron‐Irradiated Copper
Authors: Dworschak F. , Wagner H. , Wombacher P.
Published: July 2007

Lattice parameter and residual resistivity measurements were performed on high‐purity copper samples irradiated simultaneously with 2.6 MeV electrons at 6 K up to defect concentrations of about 0.1%. Lattice parameter changes could be measured with a resolution of Δa/a = 5 × 10−6. In six irradiations the ration η = (Δa/a)/Δϱ was determined as a function of defect concentration and thermal recovery. During defect production the ratio η amounts to (1.75 ± 0.10) × 103 (Ωcm)−1 and is independent of the defect concentration. Furthermore, the ratio η stays constant throughout the recovery stages I, II, and III.
Electrical and Optical Properties of Crystals with “nipi‐Superstructure”
Authors: Döhler G. H.
Published: July 2007

The zigzag‐shaped potontial in crystals with “nipi‐Superstructure” (a periodic array of n‐ and p‐doped layers, separated from each other by zones of the intrinsic material) splits the bands into subbands. As a consequence the electronic properties as a function of photon frequency or of external fields should show oscillations reflecting the subband structure. Furthermore these crystals should show interesting features, which are based on the weak interaction between carriers of different impurity layers, and on the change of the amplitude of the superstructure potential with the degree of excitation. Thus, the absorption coefficient, as well as the recombination radiation shows a strong red shift, which depends on the degree of excitation. The efficiency for light storage is high. The application of external fields has drastic effects on the absorption coefficient and on the intensity and frequency of luminescence. At high fields electroluminescence with high efficeincy eventually may be observed.
The Mechanism of F‐Center Aggregation
Authors: Paul J. L. , Scott A. B.
Published: July 2007

The rate of formation of M centers from F centers by thermal aggregation was studied in nominally pure KCl and in KCl containing oxide and sulfide ions. The process was initially about 3/2 order with respect to F‐center concetration, becoming approximately first order later. The order with respect to O2 ‐ion concentration was 0.64 ± 0.10. The activation energy was (1.06 ± 0.05) and (1.07 ± 0.05) eV in oxide‐ and sulfide‐containing crystals respectively, nearly the same as the reported jump activation energy for negative‐ion vacancies (ǒ centers) which compensate the divalent ions. The results support the two‐step mechanism F + α = F, F + F = M α, with the first step being rate‐determining. The order should be unity with respect to F‐center concentration, but deviates intially, it is believed, because of a non‐random spatial distribution of F centers at the start. Since oxide ions and α centers are strongly associated, the order should be one‐half, or somewhat greater, with respect to oxide‐ion concentration.
An Anisotropic Photon Drag Effect in Nonspherical‐Band Cubic Semiconductors
Authors: Valov P. M. , Ryvkin B. S. , Ryvkin S. M. , Yaroshetskii I. D.
Published: July 2007

The observation and a study of an anisotropy is reported of the photon drag hole current induced by linearly polarized CO2 laser light in p‐Ge and p‐InSb, which is due to the non‐spherical structure of the isoenergetic surfaces in the valence band. Besides the drag current longitudinal with respect to the photon momentum, a transverse current component appears in cases where the direction of light propagation is not along the [100] axis. The transverse current is an oscillatory function of the angle between the electric field vector and the orientation of the transverse contacts. The magnitude of longitudinal current and its polarity reversal temperature in p‐Ge depend to a considerable extent on the crystallographic orientation of the samples with respect to the photon momentum. The experimental data are in agreement with the theory.
The Diffusion of Calcium, Phosphorous, and OD−Ions in Fluorapatite
Authors: den Hartog H. , Welch D. O. , Royce B. S. H.
Published: July 2007

Experiments are reported in which the diffusion coefficients for the migration of Ca2+, PO, and OD− ions have been measured in single crystals of fluorapatite for directions parallel and perpendicular to the crystalline c‐axis. The measurements have been made over the temperature range between 1000 and 1800 K. Parallel to the c‐axis the Ca2+ selfdiffusion coefficient can be empirically represented by D∥(Ca) = 9.3 × 106exp (−5.64/kT) + 3.6 × 10−3 exp (− 2.46/kT) cm2 s−1 and perpendicular to the c‐axis by D⟂(Ca) = = 1.28 × 108 exp (−6.0/kT) + 7.92 × 10−8 exp (−1.15/kT) cm2 s−1. The diffusion coefficient of the phosphate ions is found to be at least two orders of magnitude smaller than that of calcium ions at 1700 K with D∥ (PO4) = 1.2 × 10−12 cm2 s−1 and D⟂(PO4) = 3.6 × 10−12 cm2 s−1. Preliminary data on the diffusion of OD− ions are also presented. A theoretical model for the calcium diffusion coefficients is discussed. The biological implications of the data are briefly examined.
The Behaviour of (NH4)2Cd2(SO4)3 under Pressure
Authors: Glogarová M. , Frenzel C. , Hegenbarth E.
Published: July 2007

The effect of hydrostatic pressure up to 1400 bar on (NH4)2Cd2(SO4)3 from 300 to 20 °K was studied. For pressures up to 824 bar the shift of the ferroelectric phase transition temperature, Ttr, was found ∂Ttr/∂p = + 3.35 × 10−3 deg/bar. The permittivity, ϵ, above Ttr fulfilled ∂ϵ/∂p < 0. These experimental results cannot be explained by the electrostrictive interaction only. This can be done, however, using the thermodynamic potential taking into account that the phase transition is caused by the instability in non‐homogeneous lattice vibration modes. For pressures higher than 824 bar two phase transitions occurred. It was found that ∂Ttr/∂p = −0.62 × 10−3 deg/bar and for the other transition ∂Ttr/∂p = + 10.3 × 10−3 deg/bar. At a pressure of 824 bar a triple point exists.
Velocities of Screw and 60°‐Dislocations in Silicon
Authors: George A. , Escaravage C. , Champier G. , Schröter W.
Published: July 2007

The velocities of screw and 60°‐dislocations in silicon have been measured for temperatures T between 580 and 800 °C and stresses τ between 0.1 and 3 kp/mm2. The activation energy for the movement of 60°‐dislocations Q60° is stress‐dependent in the whole stress range, that for screw dislocation Qs is constant for τ ≧ 0.4 kp/mm2 and becomes also stress‐dependent below 0.4 kp/mm2. The current theories for kink motion do not yield a satisfactory description of the experimental results.
The Lowest Conduction Band Minima of A2B4C‐Type Semiconductors
Authors: Bendorius R. , Prochukhan V. D. , Šileika A.
Published: July 2007

Studies of the influence of hydrostatic pressure up to 6500 kp/cm2 on the fundamental absorption edge of eleven A2B4C‐type compounds of chalcopyrite structure were carried out at room temperature. The large values of dEg/dP ≈ (7.3 to 10.0) × 10−6 eV kp−1 cm2 were obtained for CdGeAs2, ZnSnAs2, ZnGeAs2, CdSnP2, CdSiAs2, ZnSnP2, CdGeP2 (first group of crystals) and much smaller values ≈(—0.7 to + 1.6) × 10−6 eV kp−1 cm2 for ZnSiAs2, ZnGeP2, ZnSiP2, and CdSiP2 (second group of crystals). The comparison of these pressure coefficients with those of Γ15‐Γ1 and Γ15‐Γ1 energy gaps in A3B5 compounds leads to the conclusion that the lowest conduction band minima in the first and second groups of A2B4C crystals are Γ1 and Γ3 (or T1 + T2), respectively. This conclusion is in a good agreement with the calculated band structure of the investigated compounds and is confirmed by the studies of the slope of the fundamental absorption edge. The absorption edge of the first group of crystals is sharp due to the optical transitions Γ4 → Γ1 (derived from Γ15 → Γ1 in zincblende) and that of the second group of crystals is smooth and is caused by the transitions Γ4 → Γ3 or Γ4 → Γ1 + T2 (both correspond to indirect transitions Γ15 → X1 in zincblende).
Triplet Exciton–Charge Carrier Interaction in Anthracene
Authors: Frankevich E. L: , Sokolik I. A. , Lukin L. V.
Published: July 2007

The delayed fluorescence (DF) quenching of anthracene crystals caused by hole injection is investigated. The kinetics of DF and DF quenching due to triplet‐hole interaction are measured over a wide range of light intensities when the triplet exciton decay converts from unimolecular to bimolecular. The values of photoenhanced space‐charge‐limited current have provided the ratio of free to trapped hole concentrations in crystal. The increased role of triplet‐free hole interaction at high light intensity is shown. The rate constants of triplet‐trapped hole ((0.6 ± 0.2) × 10−11 cm3 s−1) and of triplet‐free hole ((2 ± 1) × × 10−10 cm3 s−1) interactions leading to triplet quenching are measured.
Localisation of 4d1 Electrons near Protons in MoO3, Single Crystals (ESR Measurements)
Authors: Sperlich G. , Frank G. , Rhein W.
Published: July 2007

It is shown by ESR‐measurements on differently treated single crystals of MoO3 that in these crystals the localisation of molybdenum 4d1 electrons is always connected with the presence of protons. We determine the parameters of the transferred hyperfine interaction tensor.
Short‐Range Three‐Body Potential in the First‐Order Exchange Energy and the Relative Stability of Alkali Halide Crystals
Authors: Paul S. , Sarkar A. K. , Sengupta S.
Published: July 2007

Using the Heitler‐London approach a simple expression for the first‐order exchange energy between a system of interacting atoms or ions is obtained in the S2 approximation. It is shown that this expression leads to two‐body, three‐body, and four‐body interactions only. A specific expression for the three‐body interaction is evaluated using several different approximations. Assumptions which lead to the expression previously obtained by Lundqvist are discussed. It is found that these expressions vanish for neutral particles. Some modification in the assumption is made and an expression for three‐body interaction for neutral particles is obtained. Numerical calculations are made for argon, xenon, and helium and the results compared with those obtained by others. The three‐body interaction is also applied to study the relative stability of different alkali halide structures. It is found that this three‐body potential has a strong preference for CsCl structure.
On the Stability of the Alkali Halide Lattices under Hydrostatic Pressure
Authors: Vukcevich M. R.
Published: July 2007

The high‐pressure stability of the ionic cubic lattices is considered in terms of the recently proposed “combined stability criterion”. It appears now that the phase transformation in alkali halides takes place spontaneously once the high‐pressure CsCl‐polymorph becomes mechanically stable. The relation between the new criterion and the classical thermodynamics is discussed. New experiments are suggested in order to check some of the theoretical conclusions and predictions.
Electronic Structure of Single Crystal and Amorphous Sb2, Se3
Authors: Shaffer J. C. , van pelt B. , Wood C. , Freeouf J. , Murase K. , Osmun J. W.
Published: July 2007

The near normal incidence reflectivity of Sb2, Se3 has been measured upon both crystalline and amorphous samples. The data were obtained for two polarizations (E ∥ a, E ∥ C) in the cleavage plane of the crystal. The data were Kramers‐Kronig analyzed and the implications of the results regarding the electronic structure of the compound were interpreted in terms of a valence bonding model. In particular the valence band electrons divide into those in weakly bonding resonance states and those in covalent bonding states. Upon the amorphous to crystalline transition it is the optical transitions originating in the resonance bonds which appear to be principally influenced.
Calculation of Vacancy Migration Energies in Cubic Metals Using Generalized Morse Functions
Authors: Neumann G. , Tölle V. , Hirschwald W.
Published: July 2007

The vacancy migration energies in f.c.c. and b.c.c. metals are calculated using the Morse functions of Drechsler and Nicholas. A relaxed vacancy mechanism is assumed and a radial relaxation referred to the lattice defect is admitted. The vacancy migration energies obtained as fractions of the heat of sublimation are highly dependent on the Morse constant b. The agreement between experimental and calculated energies is good as long as the Morse constant b does not exceed 4. In the case of b > 4 the calculated values for the vacancy migration energies deviate considerably from those determined experimentally, thus revealing the limits of the applicability of Morse functions to this kind of calculations.
The Optical Properties of Amorphous and Crystalline Sb2O3
Authors: Wood C. , van Pelt B. , Dwight A.
Published: July 2007

The optical properties of synthetic crystals of orthorhombic and cubic Sb2O3, are compared with those of amorphous Sb2O3 The energy gaps in the crystals were found to correspond to indirect transitions.
Thermal Transport in EuO
Authors: Martin J. J. , Dixon G. S.
Published: July 2007

The thermal conductivity of EuO has been measured from 1 to 200 K with attention to effects of magnetic order. Near the Curie point, weak critical scattering was observed. At 1 K the dominant heat carriers were found to be magnons.
Infrared Absorption and Local Symmetry of WO‐ and MoO Impurity Ions in KI and CsI Crystals
Authors: Kondilenko I. I. , Pasechny V. A. , Tsyashchenko Yu. P.
Published: July 2007

In the temperature range 120 to 800 °K and frequency range 1000 to 300 cm−1 a study has been made of the infrared absorption spectra of the impurity anions WO‐and MoO‐in KI and CsI single crystals. It is shown that W and MOO form neutral complexes W · M2+ and MoO · M2+ in KI lattice with cations M2+ (Ca2+, Sr2+, Ba2+) similar to the complexes SO · M2+, CrO · M2+ and SeO · M2+ observed earlier in the f.c.c. lattices. Here a lowering of the local symmetry to C2v of the impurity tetrahedrons results in the appearance of triplets in their vibration regions v3(A2) and v4(F2). The fine structure in the infrared spectrum of MoO · M2+ + KI was interpreted to be isotopic. A local symmetry of the impurity WO and MoO in CsI lattice was not identified unequivocally from the IR absorption spectra. The latter have doublet and quartet structure in the vibration regions v1(A1) and v3(F2), respectively, and depend on the impurity tetrahedrons and M2+ cation concentration. One, probably, should assume the interstitial formation of impurities into b.c.c. lattice of CsI which results in the existence of complex anion‐cation neutral complexes of different kinds.
Anharmonicity of Infrared Vibration Modes in the Nesosilicate Be2SiO4
Authors: Gervais F. , Piriou B. , Cabannes F.
Published: July 2007

The anharmonicity of the infrared vibration modes in phenacite Be2SiO4 has been studied by measurements of the temperature dependence of the reflectivity from 270 to 1500 cm−1. The spectra obtained in the temperature range 300 to 1500 K have been analysed by the classical dispersion theory. The cubic and quartic contributions to the anharmonicity of most of the observed modes were evaluated. From the observed dependence of mode damping on temperature and by comparison with the site symmetry method results nearly all modes have been assigned as external or internal to the tetrahedron SiO4. It is found that the cubic terms cause the anharmonicity of the internal modes, whereas both cubic and quartic terms contribute to that of the external modes.
A Born Model Calculation of the Energies of Schottky Pair Formation and Cation Migration in Potassium Azide
Authors: Danemar Å. , Welch D. O. , Royce B. S. H.
Published: July 2007

Calculations are presented for the energy of Schottky pair formation and for the activation energy of cation vacancy migration in potassium azide (KN3). Parameters for the repulsive overlap energy of the azide molecule ion have been derived from a Born model treatment of the lattice interactions with the cohesive energy and its first and second derivatives used in the fitting procedure. Three different representations of the repulsive potential are considered. Point defect calculations are performed first in a rigid lattice approximation and then with the effects of polarization and relaxation included. The polarization energy is calculated by a generalized Mott and Littleton method, which accounts for the anisotropy of the lattice, in both zeroth and first order approximations. Relaxations include displacements and rotations of nearest neighbors of the defect configurations. The sensitivity of the results t o the choice of a repulsive potential are discussed.
Vibronic Coupling and Problem of Bulk Photoconductivity in Molecular Crystals
Authors: Zgierski M. Z.
Published: July 2007

The influence of linear vibronic coupling on a charge carrier generation resulting from exciton‐exciton scattering is investigated. It is shown that the possibility of dissociation of two excitons into an electron and a hole exists with simultaneous creation of intramolecular phonons. The probability of these processes increases with temperature with an activation energy equal to the intramolecular vibrational quantum. The case of anthracene crystal is discussed.
Anomalous Magnetic Anisotropy and Resonance Linewidth in CdCr2S4
Authors: Hoekstra B. , van Stapele R. P.
Published: July 2007

The magnetic anisotropy and ferromagnetic resonance linewidth of CdCr2S4 single crystals were studied a t helium temperatures. The angular dependence of linewidth and resonance field shows anomalies near the [111], [110], and [112] direction. These are shown to be due t o impurity ions with near‐crossing levels as Fez+ on the tetrahedral site and possibly Cr2+ on the octahedral site. From calculations of the anisotropy due to Cr2+ ions it appears that, although their anisotropy can be very large, these cannot be responsible for the anomalous behaviour of non‐stoichiometric CdCr2S4 reported in the literature. It is suggested that ferrous ion impurities are responsible for this.
The Structure of Grain Boundaries. A Model Based on Planar Watching
Authors: Ralph B. , Howell P. R. , Page T. F.
Published: July 2007

A model of grain boundary structure is presented which is based on the concept of planar matching across the interface. This approach yields those displacements necessary to define the defect, population, and where possible, localisation of these displacements is seen to generate a variety of defects, some of which are analogous to the Van der Merwe dislocations in a partially coherent two‐phase interface. Thus it will be shown that the majority of grain boundaries contain dislocations with in‐plane Burgers vectors, which can be quantified both in terms of magnitude and direction, although it will be shown that the displacement patterns for the general case will be highly complex. Similarly, those dislocations which have hitherto been associated with low angle grain boundaries and coincidence‐site lattice grain boundaries can be generated by considering the matching of plane stacks.
Electron Energy Loss during Photoemission
Authors: Mahan G. D.
Published: July 2007

During the photoemission process, whereby the solid absorbs a photon and emits an electron, other excitations such as plasmons or phonons may be created. A calculation is presented of the excitation probability of both the surface and bulk form of these excitations. It is shown that electrons which originate near the surface excite mostly surface excitations, whereas those which originate deeper inside the solid have 8 higher probability of making bulk modes. The excitation rates for the hole are also included in a model which assumes that the hole is localized.
Critical Fields in Layered Superconducting Systems
Authors: Dobrosavljević L.
Published: July 2007

Layered systems are considered which behave as single, but anisotropic superconductors. Supposing a second order transition in the presence of an external field, the critical fields Hc2 and Hc3 in the GL region are calculated. Hc2 is a function of the angle θ between the magnetic field and the direction perpendicular to the layers; Hc3 depends on θ in the same way as Hc2, the ratio Hc3/Hc2 being the same as in the isotropic case (Hc3/Hc2 = 1.69). In the limiting case of thin layers it is found that Hc2 is independent of the period of the layered structure, and is larger in the parallel (θ: π/2) then in the perpendicular (θ = 0) case.
Coloration électrolytique des cristaux d'halogénures alcalins dopés au Pb2+, Sn2+ et Ge2+
Authors: Velicescu B. , Topa V.
Published: July 2007

On a trouvé que la coloration électrolytique des cristaux d'halogénures alcalins dopés avec Pb2+, Sn2+ et Ge2+ transforme ces ions en nouveaux centres trés stables (appelés centres T). Ce travail présente les propriétés optiques, Blectriques et magnétiques caractéistiques aux centres T. Ces propriétés peuvent ětre expliquées par un modéle complexe de centre T qui doit contenir des ions Pb−, Sn− et Ge−.
Elastic Constants of Polycrystals
Authors: Zeller R. , Dederichs P. H.
Published: July 2007

The elastic constants of polycrystals and similar disordered materials are calculated. Exact formal solutions for the effective tensors of the elastic constants and of the compliances are given. Analytical approximations are derived by an expansion in powers of the anisotropy. Using the t‐matrixmethod of scattering theory better approximations are obtained for highly anisotropic materials. Especially two new approximations are given, representing upper and lower bounds for the effective constants.
Dynamic Nuclear Polarization Investigations of (C6H5)3AsCH3+TCNQ Single Crystals
Authors: Deutschbein L. , Götz H. , Schulze H. , Werner K.
Published: July 2007

The paramagnetic states occurring in the anion radical salt As‐TCNQ are not merely characterized by the value of their spin quantum numbers. The doublet states are strongly localized and have a static dipole coupling, with the protons. The thermal‐excited triplet states, however, show a great mobility even at low temperatures and me in fluctuating scalar interaction with the protons. These results are obtained from measurements of dynamic proton polarization.
Optical Anisotropy of MgF, in Its UV Absorption Region
Authors: Thomas J. , Stephan G. , Lemonnier J. C. , Nisar M. , Robin S.
Published: July 2007

Reflectance measurements are used to calculate the ordinary and extraordinary optical constants of an anisotropic MgFz crystal in the energy range 11 to 28 eV. Partially linearly polarized light is used and a method of least squares is employed to compute the results. An excitonic splitting of 0.5 eV is observed at the r point. The anisotropy of the forbidden gap is 0.2 eV while that of plasmon is 0.3 eV. A tentative interpretation is given based upon a symmetry group analysis at the T point.
A Contribution to the Calculation of the Concentration of Vacancies and Complexes
Authors: Simmich O. , Löffler H.
Published: July 2007

A thermodynamic method is proposed to calculate the equilibrium concentration of both, free and bound vacancies. The formula for the entropy of mixing avoids the dependence of the sequence concerning the distribution of objects in the lattice. The lattice sites are occupied by particles of different qualities considering not only atoms and free vacancies but also complexes, requiring two or three lattice sites. The model is applied to both, pure f.c.c. metals and binary and ternary alloys. Expressions for the equilibrium concentrations are derived. The results are compared with those of other authors. Some implications and limitations of the model are discussed.
Isomer Shift of Multiple Charge States of Iron in CaO and CaF2
Authors: Regnard J. R. , Pelzl J.
Published: July 2007

The isomer shifts of Fe2+ and Fe3+ in CaF2 and of Fe2+, Fe2+, and Fe3+ in 57Co‐doped CaO have been measured by the Mössbauer effect. The results are compared with existing data of the isomer shift of multivalent iron in KMgF3 and MgO. The change of the electron density at the nucleus of the aliovalent iron is related to the covalency of the host lattices. Extrapolating to zero covalency n lower limit of the isomer shift calibration constant of 57Fe, α = −0.25(3) α30 mm s‐1, was deduced.
The Use of the Size Effect Theory in the Transport Theory of Disordered Structures
Authors: Krempaský J. , Dieška P.
Published: July 2007

The problem of transport characteristics of disordered substances having a “crystallite” structure is solved on the basis of the size effect theory. It is found that materials of this type can have the peculiarities typical for “real” amorphous semiconductors, e.g. a higher value of activation energy than half of the optical energy gap, a “mobility gap”, and a switch effect.
The Effect of a Short‐Range Three‐Body Potential on the Energy of Formation of Schottky Defects in Some Ionic Crystals
Authors: Chowdhury S. , Sen S. H. , Roy D.
Published: July 2007

The energy of formation of Schottky defects in LiF, NaCI, NaBr, and NaI is calculated including Van der Waals and the short‐range three body potential proposed by Sarkar and Sengupta in the Mott and Littleton scheme. The elastic displacement of the distant neighbours is taken in the form proposed by Boswarva and Lidiard. Due to the uncertainty in the experimental values of the elastic constants, the estimate of the three body contribution is only approximative. Considering the wide range of the experimental values of the energy of formation of Schottky defects the agreement between the calculated and experimental values is satisfactory excepting the case of NaI for which the experimental value seems to be high.
Dispersion of Phonon‐Like Surface Polaritons on α‐Quartz Observed by Attenuated Total Reflection
Authors: Falge H. J. , Otto A.
Published: July 2007

The dispersion of ordinary and extraordinary phonon‐like surface polaritons on α‐quartz has been measured on two crystallographic faces parallel and perpendicular to the c‐axis in the frequency range 350 to 1200 cm−1, covering all reststrahlen bands except the two lowest for polarization perpendicular to the optical axis. The method used was the attenuated total reflection method for transverse magnetic polarized radiation. The results are in very good agreement with theoretical calculations of the dispersion curves, using literature values for the freguencies of transverse and longitudinal optical phonons. Cut‐off wave vectors for so called “virtual excitation” surface polaritons are observed in agreement with theory.
Energy States of Isolated Donor–Acceptor Pairs and the Influence of Polarization Interaction on the Pair Energy
Authors: Bindemann R. , Unger K.
Published: July 2007

Photon energies emitted from donor‐acceptor pairs in semiconductors are calculated using a variational procedure adequate to cover also pairs of small distances. It is shown that beside the Coulomb term the polarization interaction between the two centres is essential. Polarization is involved by spherical trial functions shifted against each other. Symmetrical pairs (with equal binding energies of the isolated impurities) are considered first and asymmetrical ones by a suitable superposition of two symmetrical pairs. The agreement with experimental data taken from GaP is substantially better than the Coulomb term approximation. In the limiting case of vanishing pair distance the calculations give a finite value of the photon energy, which can be interpreted as a free exciton energy.
A New Type of the Ferroelectric Phase Transition
Authors: Holakovský J.
Published: July 2007

It, is suggested that a ferroelectric phase transition could be triggered by an instability of the crystal with respect to another phase transition parameter η. The spontaneous polarization P and spontaneous η may occur either successively or simultaneously (at the same temperature), the latter case being always a first order phase transition. The necessary condition for the existence of a triggered ferroelectric phase transition (TFT) is that η2 P2 is the lowest order interaction term in the free energy expansion. The symmetry change due to TFT is discussed.
Impurity Diffusion in B.C.C. Metals
Authors: Neumann G.
Published: July 2007

The Neumann and Hirschwald's model for the impurity diffusion in f.c.c. metals is extended on the diffusion in b.c.c. metals. A comparison of the theoretical values with suitable experimental data shows satisfactory agreement.
Temperature Dependence of Hall Coefficient and Electrical Resistivity in Sb Single Crystals at Low Temperatures
Authors: Bansal S. K. , Duggal V. P.
Published: July 2007

Measurements of the ideal electrical resistivity of single crystals of pure antimony are given in the temperature range 4.2 to 77 °K. Below 20 °K the resistivity shows a T3 dependence unlike the case of the semi‐metal Bi in which a T2 dependence is observed. The temperature variation of the Hall coefficients from 4.2 to 30 °K is presented. The Hall coefficient R23,1 decreases linearly with temperature from 4.2 to 20 °K whereas the coefficient R12,3 increases monotonously from 4.2 to 20 °K. This is in contrast with the observed behaviour of these coefficients above 55 °K. The possible causes of the observed temperature dependence of the Hall Coefficients are discussed.
Photoconductivity of KCl and KBr with F‐centres
Authors: Hoffmann H. J.
Published: July 2007

The kinetics of the photoconduction in additively coloured KCl and KBr has been investigated experimentally in the temperature range where F'‐centres decay thermally. The experimental results at high F‐ centre concentration and high illumination levels confirm the second‐order model discussed in [1]. At F‐centre concentrations below 1016 cm–3 and very low illumination levels, however, the order of the kinetics changes from second to the first order because of some additional deep traps (presumably α‐centres). Besides the concentration of additional α‐centres in the order of 1011 to 1012 cm–3, the recombination coefficient of the α‐centre and the thermal ionization energy of the F'‐centre (KCl: 0.44eV; KBr: 0.34 eV) have been determined.
Energy bands of copper chloride
Authors: Calabrese E. , Fowler W. B.
Published: July 2007

The techniques developed in a preceding paper have been applied to compute the energy bands of CuCI. Results of calculations using Slater, screened Slater, and empirically modified Slater exchange potentials are presented. The valence bands are relatively sensitive to the choice of potential, but the conduction bands are not. The calculated valence bands agree rather well with various experimental data, and slight empirical modifications are suggested to yield even better agreement. The conduction band effective mass and the band gap deformation potential are also calculated and compared with experiment.
Surface states and ionicity
Authors: Louis E. , Yndurain F.
Published: July 2007

A simple model, based on the nearly free electron approximation, is developed in order to calculate the surface state energies in heteropolar compounds using the matching of the Green's function method. The analysis is based on the effect of the crystal ionicity on the surface state energies. The results are compared with experimental data, and general trends are obtained fairly similar to the experimental evidence. Finally, the effect of using a tight‐binding model instead of a nearly free electron model to describe the crystal is studied and only minor differences are obtained.