bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractExperiments 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

AbstractThe 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

AbstractThe 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

AbstractStudies 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

AbstractThe 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

AbstractIt 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

AbstractUsing 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

AbstractThe 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

AbstractThe 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

AbstractThe 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.
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

AbstractIn 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

AbstractThe 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

AbstractCalculations 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractDuring 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

AbstractLayered 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

AbstractOn 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

AbstractThe 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

AbstractThe 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

AbstractReflectance 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractPhoton 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.