bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conversion and equilibrium between F‐ and F2‐centers in X‐irradiated KCl. II. Dynamic equilibrium experiments
Authors: Seager C. H. , Welch D. O. , Royce B. S. H. 
Published: July 2007

AbstractThe temperature dependence of the dynamic equilibrium between F‐ and F2,‐centers has been studied in KCl during X‐irradiation. Three distinct regions have been identified, a high temperature region corresponding in its temperature dependence of the equilibrium constant to the corresponding temperature range in additively colored crystals and two low temperature regions in which the equilibrium constant increases with increasing temperature with an apparent activation energy of 0.25 and 0.85 eV. A kinetic model is developed to explain these observations which involves the random creation of point defects by the radiation together with an enhanced creation probability near existing F‐centers.
The crystal field at Er3+ in copper doped zinc selenide
Authors: Lowther J. E. 
Published: July 2007

AbstractAn empirical LCAO‐MO calculation of the magnitude of the overlap contribution to the crystal field at Er3+ at an interstitial site in copper doped ZnSe is reported. The success of the point charge electrostatic model in calculating the magnitude of the crystal field at such sites is discussed.
Selbstdiffusion und isotopieeffekt in silbereinkristallen
Authors: Reimers P. , Bartdorff D. 
Published: July 2007

AbstractZwischen 673 und 954 °C wurde die gleichzeitige Diffusion von 105Ag und 110Ag in Silbereinkristallen gemessen. Die Diffusionskoeffizienten D110 sind in guter Übereinstimmung mit den kürzlich von Rothmanet el. Al. [5] mitgeteilten Werten. Der Isotopieeffekt E fällt von 0,72 bei 673 °C auf 0,58 bei 954 °C. Auch diese Daten sind mit den von Rothman et al. gemessenen Ergebnissen gut vereinbar. Die Temperaturabhängigkeit von D und E läßt sich nach Mehrer und Seeger [6] durch Diffusion über Einfach‐ und Doppelleerstellen deuten.
Radiative lifetimes of excited M and R centers in alkali halides
Authors: Bosi L. , Bussolati C. , Cova S. 
Published: July 2007

AbstractNew experimental results are given for the transition energies and for the radiative lifetimes of M and R centers in alkali halides. The experimental values of the absorption energies and of the radiative lifetime are then compared to theoretical values, calculated on the basis of a simple hydrogen‐like model.
A phenomenological theory of dielectric and mechanical properties of improper ferroelectric crystals
Authors: Kobayashi J. , Enomoto Y. , Sato Y. 
Published: July 2007

AbstractA phenomenological theory has been developed for explaining the anomalous dielectric and electro‐mechanical properties of some improper ferroelectrics. An ordering parameter 8, which plays the role of a trigger for the onset of the spontaneous polarization P is introduced into the thermodynamical potential function. The peculiar dielectric properties of (NH4)2SO4‐ and Gd2(MoO4)3‐group crystals and the anomalous behaviour of the lattice strains of Fe‐I‐boracite can be well explained on the basis of this theory. A graphical investigation in a proper θ–P plane shows how the strength of the coupling between 8 and P characterizes the transition mechanisms of the improper ferroelectrics. As a result, it has become clear that the common origin of the peculiar physical properties of both crystal groups lies in the extreme weakness of the couplings. Experimental methods to disclose improper ferroelectric mechanisms are discussed.
Wavelength modulation of the photoresponse near the indirect edges of Si, Ge, and GaP
Authors: Nishino T. , Hamakawa Y. 
Published: July 2007

AbstractThe wavelength modulation spectra for photovoltage und photoconductivity have been measured near the indirect edges of Si, Ge, and Gap. These measurements show that the structures associated with phonons can be easily resolved by a simple method. The structures corresponding to indirect transitions with emission or absorption of phonons have been observed, and the energies of some types of phonons have been estimated.
Low temperature specific heat of Fe65(Ni1 − xMnx)35 alloys
Authors: Kawarazaki S. , Shiga M. , Nakamura Y. 
Published: July 2007

AbstractLow temperature specific heat measurements were carried out for f.c.c. Fe65(Ni1 − xMnx)35 ternary alloys which cover the electron concentration range from 7.65 to 8.70. The electronic specific heat coefficient γ has a large peak against the mean electron concentration e/a around 8.5 and its peak value is 6.5 × 10−3 cal/mol deg2. On the basis of the itinerant electron ferromagnetism this large γ‐value can be explained as purely electronic origin taking the change of exchange splitting of spin up and spin down bands into consideration, and the increase in γ in the Invar region has been shown to play an important role in the sharp deviation of the average magnetic moment from the Slater‐Pauling curve. An enhancement of the γ values similar to that found by Gupta et al. in f.c.c. Fe‐Ni and Fe‐Mn alloys was observed in these ternary alloys.
Magnetic form factor of molecular oxygen
Authors: Alikhanov R. A. , Ilyina I. L. , Smirnov L. S. 
Published: July 2007

AbstractUsing neutron diffraction the magnetic form factor f of oxygen is investigated in the solid monoclinic α‐phase (T < 23.88 °K). The antiferromagnetic reflections of α‐O2 (001) and (100), containing the purely spin magnetic scattering on π‐electrons, may give the values of f for sin θ/γ equaling to 0.1047 and 0.1242, respectively. The data of magnetic diffraction on KO, are also considered: in the magnetic structure proposed the antiferromagnetic reflections (001) and (110) (sin θ/γ is equal to 0.0735 and 0.1260, respectively) are again due to the orientation of the π‐orbital spin moments (orbital moment is frozen). The whole set of obtained values f for O2 and O2 are in reasonable agreement with the calculated dependences of f.
On the kinetics of systems with discrete energy levels
Authors: Aminov L. K. 
Published: July 2007

AbstractThe nonlinear generalization of the Konstantinov and Perel diagram method is used for a derivation of the quantum kinetic equation. Under definite conditions this equation may be rewritten as a differential equation analogous to that known from the theory of paramagnetism as the Wangsness‐Bloch equation, but the relaxation term of which is not limited by the second order in a corresponding interaction. This fact allows to investigate the contribution of multiphonon relaxation processes to the rate equations for populations of the energy levels of systems with discrete energy levels. It is made clear that the relaxation parameters of the rate equations in general do not coincide with the total probabilities of transitions between levels calculated by the perturbation theory. It is shown how the procedure of the calculation of two‐phonon (Raman) transitions is modified when an intermediate level occurs inside a frequency spectrum of the lattice vibrations.
EPR investigations on Ti3+‐associated centres in hexagonal CdS single crystals
Authors: Böttcher R. , Dziesiaty J. 
Published: July 2007

AbstractEPR measurements on titanium doped CdS single crystals at T = 27 K reveal the existence of six magnetic complexes with orthorhombic structure and S = 1/2. They are attributed to defects of Ti3+ on normal Cd sites associated with an hitherto unknown acceptor like impurity replacing Cd on one of the six nearest possible Cd sites.
Black‐white contrast figures from small dislocation loops II. Application of the first order solution to small loops in ion‐irradiated tungsten foils
Authors: Häussermann F. , Rühle M. , Wilkens M. 
Published: July 2007

AbstractIn a recent paper it was shown that small dislocation loops in b.c.c. metals (in this case in tungsten, irradiated with 60 keV gold ions) show under certain diffraction conditions very special contrast figures. Theoretical contrast calculations using the analytical solution of the diffraction contrast differential equations, described in part I, are applied to the interpretation of the defect images. It is shown that the contour diagrams calculated for a variety of defect configurations and diffraction conditions agree even for fine contrast details very well with the observed contrast figures of the defects. This comparison of the theoretical and observed images allows to identify Burgers vectors and habit planes of the small dislocation loops (diameters ⪅ 50 Å).
Influence of a uniform electric field on the intraband Faraday effect
Authors: Kolesov V. V. 
Published: July 2007

AbstractThe quantum theory of the complex dielectric tensor εij(ω, q), which has been developed in [6], is extended to the case of crossed electric and magnetic fields. The quasi‐classical approximation is considered and the results are compared with earlier papers [6 to 9]. The expression for the complex conductivity tensor δij(ω, q) is used for studying the influence of the external uniform electric field on the intraband Faraday effect in semiconductors with simple band structure in two cases: the classical magnetic field and quantum limit. A brief discussion of the results is given.
Die Elektronendichteverteilung in Alkalihalogeniden und Silberhalogeniden in der Löwdinschen Näherung
Authors: Bauer R. 
Published: July 2007

AbstractFür LiF, NaF, KF und NaCl wird die Elektronendichteverteilung für Raumtemperatur in der Löwdinschen Näherung berechnet und rnit Messungen an LiF und NaCl verglichen. Die Löwdinsche Näherung wird qualitativ auf die Silberhalogenide angewendet; das Ergebnis für die Dichteverteilung und die Bindung wird mit experimentellen Ergebnissen verglichen. Die Löwdinsche Methode ist für Alkalihalogenide eine gute Näherung; zur Beschreibung der Silberhalogenide ist sie jedoch unzureichend.
Coupled plasmon‐LO phonon modes in tellurium
Authors: Selders M. , Grosse P. 
Published: July 2007

AbstractIn tellurium a coupling of the plasmons with the longitudinal polar optical phonons due to the macroscopic polarisation field is expected. The eigenfrequencies are calculated, for coupled modes propagating parallel and perpendicular to the c‐axis of the uniaxial crystal. From reflectivity measurements on heavily Sb‐doped tellurium crystals the eigenfrequencies of these modes are determined on samples with plasma frequencies nearly equal to the frequency of the polar LO‐modes.
The optical absorption of MgF2, MgCl2, and MgBr2 in the vicinity of the Mg L‐shell transitions
Authors: Rabe P. , Sonntag B. , Sagawa T. , Haensel R. 
Published: July 2007

AbstractThe Mg++ LII, III ‐absorption spectra of evaporated thin films of MgF2, MgCl2, and MgBr, have been measured in the energy range from 50 to 150 eV. Sharp absorption bands due to excitons were found at the onset of transitions from the 2p‐shell of Mg++ around 52 eV. At higher energies transitions from the 3d‐level of Br‐ and from the 2s‐level of Mg++ show up as absorption maxima. The spectra are compared with those of metallic Mg, and the corresponding alkali halides. The measurements were performed by using the synchrotron radiation of the electron synchrotron DESY.
Absorption investigations on alkaline earth fluoride mixed crystals
Authors: Görlich P. , Ullmann P. 
Published: July 2007

AbstractSome results are given of absorption investigations of alkaline earth fluoride crystals doped with impurity alkaline earth cations – CaF2:Sr, CaF2:Ba, SrF2:Ca, SrF2:Ba, and BaF2:Sr. These crystals were exposed to X‐rays at room temperature and at 84 °K. The absorption spectra recorded at these two temperatures differ considerably. The room temperature spectrum is similar to the spectrum of Li+‐, Na+‐, and K+‐doped CaF2 and SrF2 crystals, which were subtractively coloured at room temperature. The low‐temperature spectrum corresponds to a modified spectrum of the pure alkaline earth fluoride crystals after subtractive coloration. A new model of centres, the FAE centre, is suggested. In this centre one of the lattice cations, tetrahedrally surrounding the F‐centre electron, is replaced by an impurity alkaline earth cation.
Nuclear magnetic resonance in single‐crystal lead
Authors: Lüders K. , Hechtfischer D. 
Published: July 2007

AbstractNMR‐signals from an oriented lead single crystal were obtained at 4.2 K for the [001] and [110] direction parallel to the magnetic field. A spectrometer with a superconducting magnet and digital data acquisition was used. The orientation dependence of the second moments of the line was employed to determine the value of the pseudodipolar coupling constant B(rij) for the first two shells of nearest neighbours.
The transition region from paramagnetism to ferromagnetism of the transition metals and their alloys
Authors: Vogt E. 
Published: July 2007

AbstractThe terms “nearly” or “weakly” ferromagnetic mean in the collective electron theory of Stoner: the quantity αXo in the “enhancement factor” D = X/Xo = (1 – αX0)−1 is in the first case only a little smaller, in the second case only a little greater than one (X0 spin susceptibility without interaction, α molecular field coefficient). A theory developed for such cases by Wohlfarth and Edwards yields some simple expressions for the temperature or field dependence of the magnetization. The theory can be applied only on condition that the constituants of the alloy form a common d‐band (for example RhNi). But often that is not so. In such cases (e.g. RhCo), the transition from paramagnetism to ferromagnetism obviously occurs by augmentation of localized d‐states with or without magnetic moment. Some examples are described. In the system CuNi, the transition is prepared by the formation of superparamagnetic clusters at ≈32 atyo Ni; interaction of the clusters produces ferromagnetism at ≈44 atyo Ni (Kouvel and Comly).
Quantitative investigation of the n = 1 exciton line of the green series of Cu2O by a wavelength modulation technique
Authors: Daunois A. , Merle J. C. , Deiss J. L. , Nikitine S. 
Published: July 2007

AbstractThe n = 1 line of the green series of Cu2O has been investigated recently using a differential electroabsorption method. The oscillator strength of this line has also been evaluated theoretically and compared to a rough experimental measurement. In this paper, a method is developed to deduce the oscillator strength from the differential wavelength modulated spectrum and a more accurate value is obtained for the n = 1 green line. It is confirmed furthermore that this line is not polarized which implies a predominant magnetic dipole character.
Temperature dependence of the hyperfine field at iron atoms around the nonmagnetic impurities Al and Ga
Authors: Vincze I. , Cser L. 
Published: July 2007

AbstractThe temperature dependence of the hyperfine field at Fe atoms in iron‐based alloys containing Al and Ga impurities was measured by Mossbauer method between liquid nitrogen temperature and the Curie point. No difference was found in the values of the relative hyperfine fields at Fe atoms near and far from the impurity. This result is inconsistent with the prediction of a simple Heisenberg model, but is in good agreement with that of a band model.
Jahn‐Teller Effect on Transition Metal Ions in Silver Halides II. Cr2+(3d4)
Authors: Koswig H. D. , Retter U. , Ulrici W. 
Published: July 2007

AbstractThe temperature dependence of the two near infrared absorption bands of AgCl:C2+ and AgBr:Cr2+ has been measured. The low‐energy band having a temperature independent oscillator strength is assigned to the transition between the splitting levels of the 5Eg ground state. This splitting of about 6000 cm−1 is interpreted as due to a dynamic Jahn‐Teller effect. The high‐energy band is assigned to the → 5T2g transition.
Electronic States of Dislocations in Germanium
Authors: Güthm W. 
Published: July 2007

AbstractExperiments show that the optical absorption of electronic states in germanium dislocations has a pronounced polarization vector in the direction of the Burgers vector. It is concluded that electronic states split off from the energy bands arise due to the effect of stress near the dislocation lines. The calculated polarization vector of the optical transition coincides with the direction found in the experiment.
Effective Hamiltonian Method in the Theory of Activated Crystals
Authors: Nikiforov A. E. , Mitrofanov V. Ya. , Men A. N. 
Published: July 2007

AbstractA generalization of the effective Hamiltonian method (EFH) proposed in [1, 2] is developed for all SR groups and for the case of “strongly interacting levels”. Such an approach makes it possible to calculate the relative transition components in the framework of a semi‐empirical method. The proposed EFH method is based on the use of eigenfunctions the zeroth‐order Hamiltonian. This yields the possibility to evaluate the EFH parameters any order of the perturbation theory. The second part of the paper is devoted to the development of the EFH method for the calculation of the energy spectrum of a pair of coupled impurity ions in crystals.
Weak Magnetic Field Dependence of the Thermoelectric Effect in Heavily Doped Semiconductors at Low Temperatures
Authors: van Cong H. , Mesnard G. 
Published: July 2007

AbstractThe field dependence of the thermoelectric effect is studied, using a simplified model of heavily doped semiconductors, by Green's function methods and the Feynman‐path integral formulation applied to disordered systems, already developed in five previous papers. Two important cases are discussed. In the first, an ordinary n‐type semiconductor is considered, assuming that the carrier concentration is equal to the donor one; in the second, the carrier concentration is rised as the third root of the total concentration of impurities.
High Pressure ENDOR Search for the K′‐Center
Authors: Wolbarst A. B. 
Published: July 2007

AbstractAn ENDOR study of additively colored KBr was made at 10 and 11 kbar. No deviations from normal F‐center spectra were noted, indicating that the same ground state serves both F‐ and K′‐centers. A model involving stress‐distorted excited states is proposed.
Investigation of Hyperfine Field Distributions in FeSn Alloys by the Mössbauer Effect
Authors: Cser L. , Gorobchenko V. , Lukashevich I. 
Published: July 2007

AbstractHyperfine field distributions around tin impurities were investigated for both iron and tin sites. It is shown that spin density perturbations detected by the Mössbauer effect on both the iron and tin nuclei are similar. The conduction electron polarization contribution to the hyperfine field on the iron is equal to (−162 ± 18) kOe.
Coherent Magnetoelastic Effects in Ferromagnets with Impurities
Authors: Los V. F. 
Published: July 2007

AbstractThe spectrum of elementary excitations in a ferromagnet with weakly bonded impurity spins is considered in the region where the phonon frequency ωkj coincides with or is close to the excitation energy of the impurity atom spins |ω0|. It is shown that when the magnetic impurity concentration is high enough the coherent resonance magnetoelastic interaction occurs of the phonons with the low‐lying quasi‐local spin excitations which appear near the weakly bonded impurity spins. The result is that in a general case (2 S + 1) branches of the bonded collective impurity magnetoelastic excitations are formed in the resonance region ωkj ≈ |ωw0|(S is the spin of the impurity atom).
Charge‐Transfer Spectra of Transition Metal Ions in Silver Halides
Authors: Ulrici W. 
Published: July 2007

AbstractOn AgBr and AgCl crystals containing substitutional Ti3+, V3+, or Cr3+ ions absorption bands are measured in the near UV having oscillator strengths of 10−2 to 10−1. In an MO energy level scheme of the MeX cluster these absorption bands are interpreted as due to ligand‐metal charge transfer transitions. The electron is transferred from the t2 u(π) level to the t2 g(π*) level (Me = Ti, V) and to the eg(σ*) level (Me = Cr), respectively.
Electric Field Effects on Excitons in Cuprous Oxide
Authors: Brahms S. 
Published: July 2007

AbstractThe electric field induced changes of the 1S and 2S exciton states created at the E and E ± Δ0 transitions in cuprous oxide have been investigated. The ground exciton states exhibit polarization effects which have been attributed to the action of the applied field on electronic wave functions. A removal of the degeneracy of the Γ conduction band is suggested.
Interaction of Adsorbed Molecular Oxygen with Thin Superconducting Aluminum Films
Authors: Ostertag U. 
Published: July 2007

AbstractUsing tunnel diodes of the structure aluminum–oxide‐aluminum‐oxygen, a characteristic change in the density of states of thin superconducting films after covering with oxygen was found. The best fit of calculated curves to the measured characteristics was obtained for a theoretical model which assumes a pairbreaking mechanism varying locally in strength according to the local film thickness. From this fit, a maximum pairbreaking parameter and, by calculation, a maximum theoretical shift of the transition temperature is obtained. There is good agreement with the observed depression of the transition temperature.
Multiple Scattering of Thermal Neutrons by a Perfect Crystal III. Calculation of the Neutron Wave Field
Authors: Solbrig H. 
Published: July 2007

AbstractExplicite solutions for the neutron wave function are calculated for the following situations: the quasioptical case (where the wavelength is large compared with the lattice constants) and both the symmetrical Bragg‐ and Laue‐cases. The calculation is based on the results of two foregoing papers. The discussions are concentrated especially on the following two points: firstly on the quasioptical case where the crystal behaves like a homogeneous medium with a refractive index containing an effective scattering amplitude f/(1 + i k f) being real for non‐absorbing nuclei, secondly on the modifications of the standing wave fields in both the symmetrical Bragg‐ and Laue‐cases if the Bragg‐conditions are not exactly fulfilled. The theory remains applicable for strong resonance absorption by the nuclei too.
A New Model for Covalent Semiconductors with Topological Disorder
Authors: Hulin M. , Pottier N. 
Published: July 2007

AbstractA simple model is proposed, as an alternative of the LCAO formalism, to study disordered materials where the atoms are supposed to keep the same coordination number. It is shown that the possible energies can be calculated easily after the eigenvalues of the “connectivity matrix”, and that forbidden energy bands still appear, as already shown to be true within the LCAO formalism.
Isotropic Limiting Behaviour of the Six‐Dimensional Formalism of Anisotropic Dislocation Theory and Anisotropic Green's Function Theory. I. Sum Rules and Their Applications
Authors: Nishioka K. , Lothe J. 
Published: July 2007

AbstractThe isotropic limiting behaviour of the six‐dimensional anisotropic dislocation theory of Stroh [1] is studied. By means of certain sum rules, it is possible to go to the limit of isotropy without a detailed study of the degeneracies arising for the eigenvalues and the eigenvector system. The sum rules combined with the perturbation expressions of Malkn and Lothe [2] also readily give expansions for dislocation energy factors and Green's functions to the first order in the deviation from isotropy.
Crystal Field Theory of Hexagonal Fluorides of the Type ABF3
Authors: Jäger E. 
Published: July 2007

AbstractOn the basis of the point charge model the crystal field potential of hexagonal fluoroperovskite ABF3, is calculated. Explicit expressions of the distances and angles of those ions forming the ten nearest environments of a B‐ion are given. As an example the crystal field potential acting on the Ni2+ ions in RbNiF3, is Calculated. Comparison with optical spectra shows that the calculated and measured crystal field splittings 10 Dq differ by a factor 4 to 5.