bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric Properties of Single Crystals of MnO and of Mixed Crystals of MnO/CoO and MnO/NiO
Authors: Chaudhury A. K. , Rao K. V. 
Published: July 2007

AbstractDielectric constant (K′), loss (K″), and conductivity (σ) of single crystals of MnO and solid solutions of MnO/CoO and MnO/NiO have been measured as a function of frequency in the range 102 to 107 Hz and at temperatures between 30 and 450 °C. The value for K′ of MnO at 30 °C is 18.1 and practically frequency‐independent. In the solid solutions of MnO/CoO and MnO/NiO (50:50 composition) K′ decreases with frequency to a frequency‐independent value of 16.4 and 14.4, respectively. The K″‐values of the solid solutions are much larger at lower frequencies (compared to MnO). The larger values of K′ and K″ for the solid solutions at low frequencies are due to the space charge polarization. In all crystals, the dielectric constant increases with temperature but decreases with frequency. The dependence of the high‐temperature dielectric constant on frequency is attributed to the creation and destruction of dipoles at such temperatures. log ΔK′ vs. 1/T plots (where ΔK′ is the difference between dielectric constant values at any temperature T and room temperature) are straight lines for these compounds giving activation energy values of 0.57, 0.41, and 0.35 eV for MnO, MnO/CoO, and MnO/NiO, respectively. The plots of log σ vs. 1/T also give straight lines for all the crystals studied, and one obtains activation energies of 0.6, 0.52, and 0.52 eV, respectively, for the above mentioned compounds. The proximity of these activation energy values for the two processes suggest that the same charge carriers are responsible for changes in K′ and K″. The lower activation energy for the solid solutions is attributed to lattice distortion. In solid solutions, the room temperature conductivity exhibits a maximum — and the activation energy for conduction a minimum — near the composition Mn0.9X0.1O (where X stands for Co or Ni) which is explained as being due to scattering of charge carriers at larger concentrations than 10% for X.
Some Properties of Local Pseudopotentials
Authors: Brown J. S. 
Published: July 2007

AbstractIt is shown that local, spherically symmetric, non‐overlapping pseudopotentials with Coulomb tails lead to an effective interionic potential of screened Coulomb form A e−σr/r in the Thomas‐Fermi approximation. This property is related to the analytic behavior of the electron—ion form factor in the complex wavenumber plane, and is not present in RPA. The resulting form invariance of the interionic potential is discussed for several pseudopotentials in current use in the literature.
Theory of Anharmonic Crystals. I. General Formulation
Authors: Plakida N. M. , Siklós T. 
Published: July 2007

AbstractThe theory of lattice dynamics of an anharmonic crystal is developed without using the harmonic approximation as starting point. On the basis of the double‐time Green's function method the self‐consistent system of equations determining the equilibrium parameters of the lattice, the vibrational frequency and their damping is obtained. The free energy and the internal energy of an anharmonic crystal are calculated.
Current–Voltage Characteristic and Electric Field Distribution in the Systems with N‐Type I–E Characteristic
Authors: Sokolov Yu. F. 
Published: July 2007

AbstractThe boundary value problems adequate to the experimental conditions are formulated for the determination of the electric field distribution in N‐systems. These problems are analysed by the method of qualitative theory of differential equations. It is shown that: 1. In samples provided with any pair of heavy positive space‐charge layer (PSCL) and (or) heavy negative space‐charge layer (NSCL) contacts N‐type static I–U characteristics and static uniform field distributions are principally impossible in the range Up < U < Uv. 2. The I–U characteristics with current saturation regions and step‐like field distributions may be observed experimentally. If the cathode contact is a NSCL one the saturation current is equal to Ip and the field step is formed near the anode and moves to the cathode as U is increased. If the cathode contact is a PSCL one the saturation current is equal to Iv and the field step is formed near the cathode and moves to the anode as U is increased. (Up and Uv are the peak and the valley voltages of the I–U characteristic in the case of a uniform field distribution, Ip and Iv are the peak and the valley currents of a N‐type I–E characteristic.).
Dispersion Relations for Phonons in KCl at 80 and 300°K
Authors: Raunio G. , Almqvist L. 
Published: July 2007

AbstractPhonon dispersion relations in KCl at 80°K have been determined using inelastic neutron scattering. The measurements have been performed mainly in the symmetry directions [100], [110], and [111], but also at some other points in the reciprocal space. More than one third of the phonons in all branches were also studied at 300°K in order to obtain and estimate of the temperature dependence of their frequencies. A comparison is made with dispersion curves calculated by Nüsslein and Schröder for their “breathing shell” variant of the shell model for ionic crystals. The agreement for the dispersion curves is quite satisfactory in the most cases.
Analysis of Exoelectron Glow Curves
Authors: Holzapfel G. 
Published: July 2007

AbstractTerm data (activation energy, frequency factor) of electron traps in semiconductors are determined by analysing exoelectron‐emission (EEE) glow curves using the same methods which are applied on thermoluminescence glow curves. The mechanism of exoemission is generally not considered. This paper regards the influence of the work function on EEE intensity and temperature position of EEE glow curves. Corrections of EEE glow curves have to be observed at low temperatures and at small frequency factors for exact evaluations.
Investigations on the Magnetization Structure of Polycrystalline Uniaxial Ferrites with the Torsion Pendulum Method. II. Measurements on BaFe12O19
Authors: Voigt C. , Hempel K. A. 
Published: July 2007

AbstractMeasurements of the magnetic stiffness on spherical samples of polycrystalline BaFe12O19 are reported. From the results of measurements on samples with random crystallite orientation it is deduced that the fraction of those crystallites with easy axes perpendicular to the field direction which are in the single domain state decreases markedly with increasing field strength. The measurements on samples with uniaxial texture sintered at various temperatures which are performed with the preferred direction in its equilibrium position either parallel or perpendicular to the field direction establish the partial domain splitting of the crystallites. The different size and alignment of the crystallites are clearly reflected by the field dependence of the stiffness.
Infrared Electroreflectance of Zinc Oxide
Authors: Lüth H. 
Published: July 2007

AbstractElectroreflectance of ZnO is studied in the infrared spectral region (300 to 1000 cm−1) with light polarized ‖ c and ⊥ c An electric field E3 ‖ c modifies the reflectivity near both edges of the reststrahlen band. Thus the infrared eigenfrequencies can be determined by this method. From the field‐induced shift of the eigenfrequencies “electric Grüneisen constants” are calculated. They represent a measure for the dependence of the phonon frequencies upon a change of polarization.
ESR Investigation of Ni+ in Illuminated AgCl and AgBr
Authors: Höhne M. , Stasiw M. 
Published: July 2007

AbstractAgCl‐ and AgBr‐crystals, containing divalent nickel, incorported partly isolated partly in association with silver vacancies, are irradiated with light at low temperatures. Hereby the isolated nickel ions are converted to in the monovalent state.
The Influence of Sub‐Threshold Events on the Defect Production at Low Temperature Electron Irradiation
Authors: Dettmann K. 
Published: July 2007

AbstractThe general equations for the spontaneous recombination of Frenkel pairs are solved in a perturbation expansion for small defect densities. The damage rate for above‐ and subthreshold low temperature electron irradiation is calculated in linear order of the defect density.
Local Vibrations of Divalent and Univalent Complex Ions in KCl Crystals
Authors: Maksimova T. I. 
Published: July 2007

AbstractA study has been made of the infrared absorption spectra of KCl crystals containing as impurities complex ions NO, CO, and SO, as well as divalent metals Ca2+, Sr2+, Cu2+. A dependence was found of the complex ion local vibration spectra on the ionic charge. The degenerate vibrations of the divalent ions CO and SO in a crystal were shown to split whereas in the case of the univalent ions NO3 in the crystal the corresponding vibrations remained degenerate. The splitting of degenerate vibrations in the case of divalent ions is attributed to a lowering of the impurity centre symmetry resulting from a formation of complexes with anion vacancies or divalent metals.
Mechanisms Governing the Emission Processes in Nickel‐Doped Zinc Oxide
Authors: Reynolds M. L. , Hagston W. E. , Garlick G. F. J. 
Published: July 2007

AbstractThe unusual features of the emission from nickel‐doped zinc oxide are interpreted in terms of a model in which an excited transition metal ion transfers part of its energy of excitation to electrons residing in traps. This model is similar to the one developed to account for infra‐red stimulation data [1]. An important feature of the present results is that they indicate that the excitation energy of the activator can be transferred over several lattice sites to electrons residing in traps.
Über Untersuchungen an Wismutoxid‐Aufdampfschichten. I. Herstellung sowie elektrische und optische Eigenschaften
Authors: Gobrecht H. , Seeck S. , Bergt H.‐E. , Märtens A. , Kossmann K. 
Published: July 2007

AbstractEs wird über zwei Herstellungsverfahren für Wismutoxid‐Aufdampfschichten berichtet. Die nach beiden Verfahren, dem Diffusionsverfahren und der Elektronenstrahlverdampfung, hergestellten Schichten sind in ihren physikalischen Eigenschaften weitgehend gleich. Durch Röntgenstrukturuntersuchungen wird gezeigt, daß in den Schichten die α‐Modifikation des Bi2O3 vorliegt. Aus der Messung der Temperaturabhängigkeit der elektrischen Leitfähigkeit sowie aus Reflexions‐ und Durchlässigkeitsmessungen erhält man für den direkten optischen Bandabstand einen Energiewert von 2,91 eV und für indirekte Bandübergänge (optische und thermische) Energiewerte von 2,60 und 2,15 eV. Da über die Bandstruktur des Wismutoxides nichts bekannt ist, können eindeutige Zuordnungen der Valenz–Leitungsband‐Übergänge nicht gemacht werden.
The Frequency Dependence of Domain Wall Motion and Wall Bowing in Silicon–Iron Sheet
Authors: Boon C. R. , Robey J. A. 
Published: July 2007

AbstractMeasurements of 180° domain wall motion in (110) [001] grain oriented 3% silicon‐iron transformer sheet have been made under alternating magnetizing conditions up to 100 Hz. The observations were made by means of the longitudinal Kerr‐optic effect using stroboscopic illumination. Peak wall displacements for individual walls showed a very irregular frequency dependence, whereas the mean displacements gave a linear increase with increasing frequency, even for constant mean flux density. This has been attributed to domain wall bowing within the sheet. Calculations of the expected surface displacements of the walls based on domain wall micro‐eddy current theory give a good correlation with experiment.
Defects in Quenched Silicon
Authors: Swanson M. L. 
Published: July 2007

AbstractFloating‐zone refined and pulled Si crystals doped with 1015 B atoms/cm3 were quenched from 800 to 1150°C into liquid nitrogen or water. As many as 1015 donors/cm3 were created by both types of quench. No evidence was obtained, either from electrical conductivity or from photoconductivity measurements, that single vacancies, divacancies, or vacancy‐oxygen pairs were retained by the quenches. Approximately 50% of the quenched‐in defects annealed out near 300°K with a migration energy of (0.81 ± 0.04) eV. An energy level 0.4 eV from the top of the valence band was associated with these defects.
Die Absorptionskante der Selen–Tellur‐Mischkristallreihe
Authors: Sutter E. 
Published: July 2007

AbstractAn Selen–Tellur‐Mischkristallen, die nach dem Bridgman‐Verfahren hergestellt wurden und die mit jeweils um 10 At% wachsendem Tellurgehalt die gesamte Reihe zwischen Selen und Tellur überstrichen, wurde die Absorption an der Bandkante für parallel und senkrecht zur c‐Achse polarisiertes Licht gemessen. Es ergibt sich eine kontinuierliche Variation des Bandabstandes vom reinen Selen zum reinen Tellur mit einem Knick bei einem Tellurgehalt von etwa 20%. Zwischen 20 und 100 At% Tellurgehalt läßt sich die Abhängigkeit des Bandabstandes von der Tellurkonzentration C durch eine Exponential‐funktion beschreiben:

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Sowohl dieser Verlauf als auch die sehr starke Konzentrationsabhängigkeit des Bandabstandes für kleine Tellurgehalte in Selen geht parallel mit der Variation des Bindungswinkels der Atome in der Mischkristallreihe. Der spektrale Verlauf der Absorptionskonstanten in der Kante entspricht der Theorie für indirekte Übergänge.
Study of the Sublattices Magnetisations in Mn0.6Zn0.4Fe2O4 by Neutron Diffractometry and Mössbauer Spectrometry
Authors: König U. , Gros Y. , Chol G. 
Published: July 2007

AbstractThe temperature dependence of the two sublattices magnetisations of Mn0.6Zn0.4Fe2O4 was determined in order to study the superexchange interactions in Mn2+–O2+–Fe3+ linkages. The tetrahedral and octahedral sublattices magnetisations were obtained in absolute scale by neutron diffractometry. Moreover by Mössbauer spectrometry the octahedral sublattice magnetisation was determined in a relative scale as a function of temperature. The results obtained by both methods show the same temperature dependences within the experimental accuracy. The Mössbauer spectra recorded at temperatures higher than 100°K show line broadening and overlapping indicating relaxation effects. The molecular field parameters were deduced from the experimental results on the basis of the Néel model. The best agreement is found for JAA = 0, JAB = (−19 ± 1)°K, and JBB = (4.7 ± 2)°K. The failing B moment and the evidence for a positive B–B interaction are discussed.
Spectroscopic Investigation of Cu+ and Ag+ Centres in Alkali Halides under High Hydrostatic Pressure
Authors: Niilisk A. , Laisaar A. 
Published: July 2007

AbstractThe effect of hydrostatic pressure up to 6000 kp/cm2 on the excitation and emission spectra of Cu+ and Ag+ centres in alkali halides is studied. In all crystals, the blue shift of both the emission band and the low‐energy side of the excitation spectrum is observed, the emission band shift being greater. The analysis basing on a single configuration‐coordinate model shows that the pressure shifts of Cu+ and Ag+ spectra are caused mainly by the change (increase) of the pure‐electronic transition energy. The results obtained confirm the conclusion about the genetic relation between these spectra and the electronic transitions d10 ⇄ d9 s in free Cu+ and Ag+ ions. For a few crystals the effect of pressure on the luminescence decay is measured. Possible reasons for the change of τ by the lattice compression are discussed.
Theoretical Studies on the F‐Centre in Alkali Halides
Authors: Evarestov R. A. , Treiger V. M. 
Published: July 2007

AbstractThe results of the theoretical study of the electronic states of the R+‐centre in alkali halides are reported. No empirical parameters are used in this calculation. The electronic core polarization is taken into account. The results of the calculation are in satisfactory agreement with the experimental data and can be considered as a theoretical confirmation of the F3+‐model of the R+‐centre.
Influence of Zero‐point Vibration on the Superhyperfine Interactions of Hydrogen and Deuterium Centres in KCl
Authors: Spaeth J. M. 
Published: July 2007

AbstractThe superhyperfine (shf) interactions of D centres were measured by ENDOR and compared with those of H centres (H = H atom on interstitial lattice position). The isotropic shf constants of the nearest K and Cl neighbours are smaller for D centres than for H centres: aH(K)/aD(K) = 1.165 and aH(Cl)/aD(Cl) = 1.026. In a model calculation it is shown that the large difference in isotope effect of the K and Cl neighbours can be understood as a consequence of the overlaps of their ion cores. At least 30% of aH(K) and 10% of aH(Cl) are only due to zero‐point vibration of the H atom.
Neutron Inelastic Scattering Studies in Crystal Hydrates
Authors: Thaper C. L. , Sequeira A. , Dasannacharya B. A. , Iyengar P. K. 
Published: July 2007

AbstractNeutron inelastic scattering studies on polycrystalline samples of K2C2O4 · H2O, Ba(ClO3)2 · H2O, Li2SO4 · H2O, CaSO4 · 2H2O, CuCl2 · 2H2O, and BeSO4 · 4H2O have been performed at room temperature and 100°K with the aim to observe the librational frequencies in these hydrates. Deuterated salts were studied to confirm the librational modes. Within the experimental resolution, it is possible to observe two librational peaks in favourable cases. A definite assignment of these peaks could not be made even by comparison with other available data. Vibrational frequencies in K2C2O4 · H2O, Ba(ClO3)2 · H2O, and BeSO4 · 4H2O have been obtained from crystal energy consideration. From their comparison with the observed frequencies it may be seen that the nearest‐neighbour hydrogen bond is the dominant interaction for the calculations of the librational frequencies in these salts.
Ferromagnetic Resonance in Thermally Processed α‐Fe2O3
Authors: Pietrzak J. , Klimaszewski B. 
Published: July 2007

AbstractFerromagnetic resonance is observed in the 1.25 cm microwave band in polycrystalline hematite samples after subjecting them to high‐temperature pulses in air. The intensity and width of the resonance line are found to depend on the duration of the horizontal part of the pulse and on the cooling rate. This ferromagnetic resonance absorption is shown to be related with the formation of a ferromagnetic phase structurally identic with magnetite.
Propriétés des alliages InSb1−xBix I. Mesures électriques
Authors: Jean‐Louis A. M. , Hamon C. 
Published: July 2007

AbstractNous avons mis en évidence l'existence de solutions solides InSb1−xBix avec x ≦ 2,2%. Des mesures d'effet Hall et de conductivité effectuées sur des monocristaux de compositions variées, dans l'intervalle de température 77 à 435°K, sont analysées à l'aide du modèle de Kane. Les résultats, en bon accord avec ce modèle, montrent que la présence de bismuth dans l'InSb entraîne un rétrécissement de la bande interdite à 0°K, et une diminution du coefficient de température γ. La variation de E est d'environ 3,8 eV par mole de Bi.
Propriétés des alliages InSb1−xBix II. Absorption Optique
Authors: Jean‐Louis A. M. , Ayrault B. , Vargas J. 
Published: July 2007

AbstractNous avons mesuré à différentes températures, l'absorption optique d'alliages semiconducteurs InSb1−xBix. Les corrections usuelles dues à l'absorption par porteurs libres et à l'effet Burstein, permettent d'en déduire l'énergie de bande interdite. Les résultats sont en excellent accord avec ceux déduits des mesures d'effet Hall (article précédent) et montrent une décroissance ΔEG/Δx de 3,6 eV par mole. La variation de EG(T) est linéaire pour T ≧ 80°K et le coefficient de température γ = ‐ΔEG/ΔT décroît avec la concentration en bismuth. – L'introduction de Bi dans le réseau d'InSb conduit donc à la décroissance de EG et de γ. Ces effets sont similaires à ceux mis en évidence globalement dans les composés III–V quand le poids atomique des constituants augmente.
Low Temperature Thermopower of Aluminium
Authors: Holwech I. , Sollien V. 
Published: July 2007

AbstractThe thermopower of zone refined aluminium doped with copper and iron has been measured as a function of temperature and specimen thickness in the residual resistance range. It is shown that the size dependence can be used to separate the “scattering” contribution and the “density of states” contribution to the diffusion thermopower. The phonon drag thermopower is found to be different in the two alloys, while the “density of states” contribution is found to be in agreement with the free electron value.
Some Effects in AIIBVI Crystals in High Electric Fields Related to the Temperature Quenching of Photoconductivity
Authors: Kalashnikov S. G. , Pustovoit V. I. , Pado G. S. , Tokarev E. F. 
Published: July 2007

AbstractHighly inhomogeneous distributions of the electric field strength, of the current, and of the temperature may arise in photoconductive AIIBVI crystals in strong electric fields. The distributions may be parallel to the current and transversal to it. The phenomenon is due to a combination of two processes – the temperature quenching of photoconductivity and the Joule heating. In the case of the transversal inhomogeneity the current lines are forced towards the surface of the sample. In the case of the longitudinal inhomogeneity the region of high electric field and elevated temperature occurs inside the sample. Under certain conditions this region becomes unstable and spontaneous infralow current oscillations arise. The importance of these phenomena is pointed out for the ultrasonic amplification by drifting electrons in photoconductive materials.
Structure of an Amorphous FePC Alloy
Authors: Lin S. C. H. , Duwez P. 
Published: July 2007

AbstractThe structure of an amorphous Fe80P13C7 alloy obtained by rapid quenching from the liquid state has been studied by X‐ray diffraction. An analysis of the radial distribution function indicates that the first four nearest neighbors are located at distances of 2.6, 4.3, 5.1, and 6.7 Å. The number of the first nearest neighbors is 13.1 and is dominated by FeFe atom pairs. The structure of the alloy can be described by a randomized b.b.c. iron in which the iron atoms have the first nearest neighbor number 13.6 at a distance of 2.6 Å.
Electronic Energy Bands, Excitons, and Plasmons in Lithium Fluoride Crystal
Authors: Kunz A. B. , Miyakawa T. , Oyama S. 
Published: July 2007

AbstractThe electronic band structure of lithium fluoride has been worked out using the mixed basis (MB) method recently proposed by one of the authors. Due to the effect of exchange, F− wave functions are rather compact, and mixing of plane waves in the valence band wave functions is unimportant. The minima of the conduction band occur at equivalent L‐points in the Brillouin zone. Recent ultraviolet, soft X‐ray, and electron energy loss spectra are analyzed in the light of the present calculation.
Analytic Form of Stress Fields, Displacements, and Dilation for the 〈111〉Dislocation in Anisotropic Elasticity
Authors: Steeds J. W. 
Published: July 2007

AbstractScrew, edge, and mixed dislocations are treated by a new method which is simple to handle. Labour saving equations are derived which further shorten the algebraic processes. The results emphasize the need for anisotropic expressions in the case of common cubic materials, and are presented in a form which shows their relation to the isotropic expressions.
Ferromagnetic Structures in Polycrystalline Films with a Magnetic Field Applied Perpendicular to the Film Plane
Authors: Hothersall D. C. 
Published: July 2007

AbstractWhen a ferromagnetic thin film mounted on an electron microscope grid is placed in a magnetic field perpendicular to the grid a change of domain configuration occurs which depends upon the relief of the film. Domain configurations of this type in low anisotropy polycrystalline iron and cobalt films are discussed. The domain boundaries in these conditions are of the “head‐on” type in which the magnetization rotates through 180° in the wall but lies perpendicular to the wall axis on either side of it. A simple analysis of the head‐on structure enables a quantitative estimate of the amount of buckling in a film to be made. The domain structures at the edges of thin films in the applied magnetic field are also considered.