bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrogenic Impurity Bands in an External Magnetic Field
Authors: Lukes T. , Nrx B. , Rogers B. , Suprapto B. 
Published: July 2007

AbstractA method used previously to investigate the influence of charged donors on the density of states when an impurity band is formed is extended to the case when a magnetic field is present. The density of states is calculated for various magnetic fields for concentrations typical of InSb at the metal–insulator transition. For sufficiently low concentrations splitting of the baud can take place as in the absence of a magnetic field.
Diamagnetism and Superexchange Electron Interaction in Cs2Sb (IV) Cl6, Semiconducting Crystals
Authors: Ionova G. V. , Ionov S. P. , Makarov E. F. , Aleksandrov A. Yu. 
Published: July 2007

AbstractCrystals of Cs2Sb SbCl6Sb are diamagnetic and have a cubic structure of the antifluorite type. These facts may be explained either in terms of statistical disorder between Sb(III) and Sb(V) or in terms of electron exchange between SbCl and SbCl. A calculation is presented of the exchange interaction between the nearest SbCl complexes. The exchange integral £ is taken in form £ = (Es − Et)/2 where Es and Et are energies of singlet and triplet states. It is established that CI atoms mainly contribute to the exchange interaction. Sign and value of the exchange integral correspond to an antiferromagnetically ordered state in Cs2SbCl6 at room temperature.
Cation Diffusion in Single Crystal MgO up to 2500 °C
Authors: Harding B. C. 
Published: July 2007

AbstractThe diffusion of Ca2+ and Ge4+ in single crystal MgO has been studied over the temperature range 1850 to 2400 °C using a sectioning technique. The activation energy for the diffusion of Ca2+ (3.2 eV) is similar to the values obtained for other divalent cations at the same temperatures, but the value for Ge4+ (4.0 eV) is significantly greater. For ions of a given valence, it is concluded that the activation energy for diffusion in MgO is independent of the “hard‐sphere” ionic radius of the diffusing ion, while the pre‐exponential factor, Do, appears to depend on its mass and electronic polarisability. If results for aliovalent ion diffusion are interpreted in terms of the association theory developed for the alkali halides, an empirical relation between the charge of the diffusing ion and its enthalpy of migration emerges.
Effective Charges and Lattice Dynamics of Zineblende Structure Crystals I. Effective Charges
Authors: Mani K. K. , Singh R. P. 
Published: July 2007

AbstractThe cohesive energies of the zineblende and wurtzite structure are expressed as a sum of covalent and ionic parts. It is shown that the Lippincott potential function is a good representation of the covalent contribution and that effective charges may be obtained from the experimental bulk moduli and the Lippincott function. These charges are compared with other estimates. Heats of atomisation for a series of II–VI and III–V compounds are correlated.
NMR and Magnetic Susceptibility of Cr2Al11
Authors: Coldea M. , Crisan M. , Niculescu V. , Pop I. 
Published: July 2007

AbstractThe temperature dependence of the magnetic susceptibility and the Knight shift are measured. The magnetic susceptibility has a minimum around a temperature of To≈ 400 K and for the Knight shift a quadratic dependence of the temperature is found. The NMR and magnetic susceptibility measurements are correlated and the results are discussed in terms of localized Anderson magnetic moments and spin fluctuations. The expression found for the magnetic susceptibility from a theoretical model is in good agreement with experimental results.
Polarization of Singlet–Triplet Transitions in Perylene‐Type Molecular Crystals
Authors: Witkowski A. , Zgierski M. Z. 
Published: July 2007

AbstractThe polarizations of singlet–triplet transitions in molecular crystals with four molecules in the unit cell and group symmetry C52h are analyzed. It is shown that only transitions to factor group symmetry forbidden triplet states possess intensity and are no longer polarized perpendicular to any crystal axis.
Polarized luminescence and the mössbauer effect of tin impurity centres in NaCl crystals
Authors: Realo E. , Zazubovich S. 
Published: July 2007

AbstractAn investigation is made of various types of impurity centres in NaCl;Sn and KCl:Sn crystals using the Mössbauer effect and polarized luminescence. Two types of Sn2+ centres are found in NaCl: Sn. The centres of type I have polarized emission at 2.78 eV due to electronic transitions allowed along the C4 axis of the crystal. A small quadrupole splitting (<0.4 mm/s) of the Mössbauer absorption line at +4.32 mm/s is observed for these centres. The centres of type II show the polarized emission at 2.3 eV due to electronic transitions allowed along the C2 axis of the crystal. For these centres a considerable value of quadrupole splitting Δ = 0.97 mm/s of the Mössbauer lines with the isomer shift + 3.75 mm/s is found. Only the centres of the type I are found in KCl: Sn crystals. It is supposed, that the investigated centres in NaCl:Sn represent two types of associates of Sn2+ ions with cation vacancies vc: associates with C4V symmetry (the type I centres) and associates with C2v symmetry (the type II centres) in the ground electronic state.
Influence of acceptor concentration on the hall effect in tellurium
Authors: Bastard G. , Hau Nguyen Hy , Rigaux C. , Vieren J. P. 
Published: July 2007

AbstractExperimental observations and new theoretical calculations are given of the impurity influence on the valence band population in tellurium. Galvanomagnetic measurements were performed at temperatures between 1.6 and 77 K, in magnetic fields up to 60 kG, on samples with acceptor concentrations from 1014 to 2 × 1016 cm–3. The temperature and the magnetic field dependences of the Hall coefficient R1 in low doped samples (NA < 2 × 1015 cm–3) is quantitatively explained by the “two acceptor levels” model proposed by Thanh. Results observed for a higher density of acceptors show the presence of an impurity band above the valence band.
Theory of bloch wall tunnelling
Authors: Egami T. 
Published: July 2007

AbstractThe quantum mechanical tunnelling of a very narrow Bloch wall through the intrinsic barrier is considered. A microscopic theory of the spin wave description of narrow domain walls is developed and subsequently extended to describe the domain wall tunnelling phenomena. The tunnelling probability is presented in two ways, firstly, by the quasi‐particle approach using the conventional W.K.B. approximation and secondly by the method of direct product of state vectors. These two methods are complementary to each other. The results indicate that below the temperature of liquid helium the domain wall diffusion in the rare earth metals and compounds which exhibit high intrinsic coercivity is likely to be governed by the tunnelling process.
A perturbation method for calculating absorption coefficients of degenerate bloch waves in the dynamical theory of electron diffraction
Authors: Sheinin S. S. , Cann C. D. 
Published: July 2007

AbstractThe standard method for calculating absorption coefficients in the dynamical theory of electron diffraction is based on perturbation theory for the non‐degenerate state. The presence of Bloch wave degeneracies, such as those which occur in the critical voltage case or in the presence of certain non‐systematic reflections, requires that a different approach be adopted. A method based on perturbation theory for the doubly degenerate state has therefore been developed. Application of this method to the critical voltage case indicates that the errors obtained in using the standard approach depend on the strength of the systematic reflections in the row involved. In the non‐systematic case, application of this method to the calculation of intensities gives results in agreement with those obtained from diagonalization of the complex matrix.
Investigation of the electron energy spectrum in some phases of CsCl‐type
Authors: Nemoshkalbnko V. V. , Ya. Nagorny V. , Nikolaev L. I. , Mindlina M. A. , Gigolashvili G. P. 
Published: July 2007

AbstractThe results of X‐ray spectral investigations of some phases of the CsCl‐type composed by alloying of a series of transition metals of the first, second, and the third main periods are presented. The K, L, and M emission bands of the atoms constituting the alloys are investigated. Some conclusions about the type of interatomic interaction and the nature of bonding in the considered compounds are presented.
Non‐conservation of quasiparticles and bound states
Authors: Dordević R. , Ivezić T. , Tošić B. S. , Žakula R. B. 
Published: July 2007

AbstractAn analysis is made of bound states in systems in which the number of quasi‐particlea is not conserved. All calculations are performed using the exact Bose representation of the Pauli operators as well as the Dyson‐Maleev representation, and corrections to the bound state energies with respect to Heitler‐London approximation are found. It is also shown that in this case the approximate second quantization method does not give the correct zero‐order spectrum of the free excitations.
Antiferromagnetic Resonance in CuCl2 · 2 H2O in Inclined Magnetic Field near Intermediate State
Authors: Galkin A. A. , Kovner S. N. , Popov V. A. 
Published: July 2007

AbstractDetailed experimental and theoretical investigations of the resonance properties of biaxial antiferromagnetic CuCl2 · 2 H2O are made in the range of low frequencies v = 0.65 to 5.2 GHz at T = 1.57°K in an increasing external magnetic field H. The theory shows a satisfactory agreement with the experiment.
A Localized Soft Mode Theory for Martensitic Transformations
Authors: Clapp P. C. 
Published: July 2007

AbstractAnharmonic terms of the elastic free energy of a solid are used to locate a surface of instability or “strain spinodal”. The strains near lattice defects bring some regions close to the strain spinodal causing a rapid change in local elastic properties and resulting in localized “soft mode” centers. These regions are proposed as the primary nucleation sites for martensitic transformations. A number of experiments are proposed to test the physical aspects of the theory and some recent evidence is cited supporting several features of the model.
Piezoelectricity in Zincblende‐ and Wurtzite‐Type Crystals
Authors: Hübner K. 
Published: July 2007

AbstractA phenomenological model for the piezoelectric effect in zincblende‐ and wurtzite‐type crystals is proposed on the basis of optic and dielectric lattice properties. By introduction of a deformation charge it is shown that the sign of the longitudinal piezoelectric constant is determined by the ionicity of the chemical bond. The piezoelectric constant is calculated with correct sign and found to be in good numerical agreement with experimental data. For a number of I–VII, II–VI, and III–V compounds piezoelectric constants are predicted. With the piezoelectric effect the sign of the dynamic effective charges is determined.
On the Pre‐Exponential Factor in the Rate Equation for Plastic Flow
Authors: Sueek T. , Luton M. J. , Jonas J. J. 
Published: July 2007

AbstractAlthough it is not generally possible to calculate the pre‐exponential factor ϵ0 directly from experimental results, the assumption that the obstacle‐dislocation interaction has the same temperature dependence as the shear modulus permits ϵ0 to be determined from the available data. An iterative procedure is described which, when convergent, is consistent with the thermodynamic properties of such obstacles. The approach is applied to high temperature yield data for zirconium and the results are compared with various physical models for the pre‐exponential term. The values of the activation parameters and their dependence on stress and temperature are consistent with the interpretation that the rate controlling process in the high temperature yielding of zirconium is the unpinning of the nodes associated with a specific group of segment lengths selected from the total segment length distribution present within the material.
Structural and Electronic Properties of a Clathrate‐Like Model of Amorphous Germanium
Authors: Henderson D. 
Published: July 2007

AbstractThe tetrahedral network of the xenon hydrate structure exhibits bond distortions and five‐atom rings. Hence, this clathrate network is a simple model of amorphous Ge which is presumed to contain these structural elements. The radial distribution function and electronic density of states, using a tight‐binding Hamiltonian, are calculated for this model and are found to have many similarities with those of amorphous Ge.
Linear Magnetic Birefringence in the Antiferromagnetic Iron Group Difluorides
Authors: Jahn I. R. 
Published: July 2007

AbstractThe linear optical birefringence of the iron‐group difluorides (rutile‐type) has been determined between 5 and 700 K. A magnetic contribution to the birefringence occurs during the ordering of the antiferromagnetic compounds MnF2, FeF2, CoF2, and the weak ferromagnetic NiF2; the linear magnetic birefringence (LMB) can be well separated from the temperature dependent natural optical anisotropy. Both the magnetic short‐range as well as the long‐range order contribute to the LMB. The temperature derivative of the LMB follows the course of the magnetic specific heat to a very good degree. It is shown that this proportionality is to be expected if all spin pair correlation functions exhibit the same temperature behaviour. Whether this condition is valid for the lattice distortions is discussed using the existing structural data. Assuming the observed LMB is mainly due to spontaneous lattice distortions, the influence of the fluorine parameter seems to play an important role.
Production of F and F‐Aggregate Centres in CaF2 and SrF2 by Irradiation
Authors: Hayes W. , Lambourn K. F. 
Published: July 2007

AbstractThe efficiency of production of F centres in CaF2 by X‐irradiation has been studied as a function of temperature and compared with the results of an earlier detailed investigation of SrF2 [1]. The efficiency begins to fall gradually at about 20 K and at 100 K has reached a very low value. It does not recover at higher temperatures. It is found that M+, M, and R centres can be produced in CaF2 and SrF2 after heavy irradiation with 1 MeV electrons at 77 K. The measured optical properties of these centres are identical with those found in additively coloured crystals. Mechanisms for the production of F and F‐aggregate centres in irradiated crystals are discussed.
Influence of Free Carriers on the Faraday Rotation and Faraday Ellipticity in the Exciton Absorption Region of GaAs
Authors: Zvára M. , Prosser V. 
Published: July 2007

AbstractInvestigations of n‐GaAs samples with different free carrier concentrations, both, below and in the absorption edge region, confirm the dominating influence of exciton transitions in Faraday rotation and Faraday ellipticity spectra. The theoretical curves, taking into account exciton and Landau level contributions in the real hand structure of GaAs, show good qualitative agreement with experimental data.
The Effective Charges of Fe Impurity Atoms in AIIBIVC Crystals from Mössbauer Studies
Authors: Yarmarkin V. K. , Teslenko S. P. , Dubrovskii G. P. , Grekov F. F. , Prochukhan V. D. 
Published: July 2007

AbstractResults of Fe57 Mössbauer measurements are used for the analysis of the electronic state of Fe impurity atoms in AIIBIVC ternary compounds. The Mössbauer parameters have been analyzed and the effective charges of the Fe impurity atoms are evaluated on the basis of a MO (molecular orbital) cluster formed by the central Fe atom and the atoms of the matrix compound located in the two first coordination spheres in the AIIBIVC crystal. The possibility of using the results obtained for the analysis of the state of Fe impurity atoms in AIIIBV binary compounds is discussed.
Temperature Dependence of the Resistivity in a Kondo System: Influence of the Crystal Field
Authors: de Gennaro S. , Borchi E. 
Published: July 2007

AbstractUsing the s‐f exchange model the influence of the crystal field is examined on the temperature dependence of the resistivity for a Kondo system. The case of a cerium impurity ion in a lattice of cubic symmetry is considered. An exact algebraic expression for the resistivity versus temperature is obtained. Some resistivity versus T curves are reported and discussed.
Modulated Spectroscopy of Cubic Semiconductors. Calculation of Piezomodulation Parameters for Degenerate Semiconductors
Authors: Mathieu H. , Auvergne D. , Camassel J. 
Published: July 2007

AbstractThe effects of a modulating strain on an M0 critical point structure in reflectivity are considered for a study of degenerate semiconductors for which the kinetic energy of excited carriers is greater than the energy threshold modulation. Using the Pikus‐Bir formalism to describe the strain induced change in the valence band of cubic compounds, optical matrix elements and modulation amplitudes for several strain arrangements are calculated. For (001) and (111) strains, it is shown that the strain modulated part of ΔR can be described by an effective modulation ΔẼg which is independent of the kind of carriers (light or heavy holes) involved in the transition.
Single Impurity Effect on the Electron—Hole T‐Matrix in Gadolinium
Authors: Holz A. 
Published: July 2007

AbstractAn interpretation of the large 15 μΩcm per at% residual electrical resistivity of Mg in a Gd host is suggested in terms of the formation of bound interband electron—hole states at the Mg site. The theory is developed for a single Mg ion in a Gd host and allows a qualitatively correct interpretation of the experiments. According to an order of magnitude estimate an instability of the paramagnetic ground state in the presence of a single Mg ion seems to be possible when band structure effects on the screening of the Coulomb interaction are taken qualitatively into account.
Excitation Spectra of Luminescence in Cadmium Sulfide
Authors: Planel R. , Bonnot A. , la Guillaume C. Benoità 
Published: July 2007

AbstractExcitation spectra of the excitonic luminescence in CdS are presented for three types of samples: doped, pure, and surface contaminated samples. The positions and relative magnitudes of peaks appearing in some of these spectra are analyzed and quantitatively explained in terms of indirect creation of free excitons. The different behaviour of the three types of samples investigated allows a more general discussion which leads to important discriminations between direct and indirect optical absorption and between volume and surface radiative recombination.
Friedel's Law in Electron Diffraction as Applied to the Study of Domain Structures in Non‐Centrosymmetrical Crystals
Authors: Serneels R. , Snykers M. , Delavignette P. , Gevers R. , Amelinckx S. 
Published: July 2007

AbstractIt is shown that a strong contrast may arise in dark‐field electron microscope images between two crystal parts related by an inversion operation, as a result of the violation of Friedel's law. Friedel's law is violated only in the diffracted beam and only in cases where a multiple‐beam situation prevails. Moreover the excited reflections must belong to B zone which reveals the non‐centrosymmetrical character of the crystal. The interfaces between two domains related by an inversion operation, which are proposed to call inversion boundaries are imaged by α‐like fringes which nevertheless have properties which differ somewhat from those of pure α‐fringes. These considerations are applied to the domain structure observed in the γ‐phase. In this case the inversion boundaries separate regions which have suffered displacements as well. It is shown that the displacement vector of such boundaries can be given an unambiguous meaning, although strictly speaking the structures in the two parts cannot be derived one from the other by means of a parallel displacement. It is demonstrated in a concrete case that the observed contrast can be accounted for by a four. beam calculation.
Thermally Activated Dislocation Motion past Point Obstacles Including the Effects of Dislocation Shape
Authors: Dimelfi R. J. , Nix W. D. 
Published: July 2007

AbstractThermally activated motion of dislocations past point obstacles is studied by treating a special case of radially symmetric obstacles created by considering a position dependent dislocation line energy. Detailed consideration of the shape of the dislocation in the equilibrium and activated states is made by applying the techniques of the calculus of variations. The activation energy is calculated as a function of the applied stress and the shape and height of the obstacle. It is shown that the stress dependence of the activation energy is similar in form to that found for linear obstacles by Dorn and Rajnak. An estimate of the activation area, made by directly integrating the shape of the dislocation, compares favorably with the activation area found by considering the stress dependence of the activation energy. The shape of the dislocation in both the equilibrium and activated states is also calculated. Two athermal stress levels for the point obstacle problem are identified and studied. These involve dislocation bowing between obstacles and athermal cutting of the obstacles, respectively.
Optical Photoionization Spectra of CdSe:Cr
Authors: Jastrzębski L. , Baranowski J. M. 
Published: July 2007

AbstractIt is shown that the absorption tail in CdSe:Cr (d4) is due to photoionization of Cr impurities. The absorption spectrum is well described by a formula proposed by Allen in a wide range of Cr concentration ranging from 5 × 1017 to 5 × 1019 cm−3. The value of the matrix element of the optical transition from Cr (d4) to the conduction band suggests that the transition is from the extended s‐like bonding orbital rather than from 3d orbital. For high Cr concentrations about 1019 cm−3 interaction effects between impurities occur. It is also shown that two charge states: Cr2+ and probably Cr3+ are possible in CdSe.
Simulation of Positron Channeling in Single Crystals
Authors: Kudrin V. V. , Timoshnikov Yu. A. , Vorobev S. A. 
Published: July 2007

AbstractA simulation method of charged particle scattering in a crystal lattice is described. Angular distributions of protons and positrons leaving the crystal are calculated and the orientational distributions of axial channeling particles are received. The influence of the experimental geometry and the crystal condition on the obtained results is discussed. It is shown that binary collision calculation gives agreement with experimental results.
On the Problem of Cross Relaxation in Systems with Different Axes of Quantization
Authors: Korsava L. G. 
Published: July 2007

AbstractSpecimens with two different types of spins S and I are considered. There is a slight difference between their Zeeman energies and the dependence of the cross‐relaxation probability (1/T12)on the angle between the axes of spin quantization is considered in the general form. It is shown that 1/T12, increases almost by an order of magnitude when the angle between the axes of spin quantization change from 0 to π. In addition, the problem of cross‐relaxation probability is considered for a system of non‐equivalent non‐Kramers S and I ions (doublets). The dependence of 1/T12 on the value of the constant magnetic field and on the parameters Δ of the Hamiltonians of non‐Kramers doublets is obtained. In particular, it is shown that in a simple case 1/T12∼1/H.