bluuebunny/crossref_metadata_2025 huggingface dataset:
Capacitances and Differential Negative Resistances of MIM Structures
Authors: Bernard J. , Delacote G. , Mentalecheta Y.
Published: July 2007

A study has been made of the oxide thickness dependence of the capacitance and the current—voltage characteristics (at 10−5 Torr) of the structures AlAl2O3Au. The thicknesses varied from 25 (oxide formed at air) to 500 Å. The value of the apparent dielectric constant decreases for very thin oxide films. Differential negative resistances have been observed for all diodes. The voltage for the minimum current and the current and the current after the minimum increase linearly with the thickness of the oxide. The results are explained by the existence of a high resistance domain with a thickness of about 10 to 20 Å at one of the metal oxide interfaces, probably the interface AlAl2O3. The decrease of the current is perhaps caused by an increase of the thickness of the domain. Structures with thicknesses of oxide e > 400 Å show a broad current maximum which is sometimes splitted in two maxima.
Theoretical Studies on the M′‐Centre in Alkali Halide Crystals
Authors: Evarestov R. A.
Published: July 2007

The results of the theoretical study of the electronic states of the M′‐centre in alkali halides are reported. No empirical parameters are used in this calculation. – The electronic core polarization is taken into account (within the limits of model of the polarizable point ion lattice), and is found to be essential for the charged M′‐centre. The results of the calculation are in good agreement with the experimental data for KCl and KBr crystals and can be considered as a thoretical confirmation of the F‐model of the M′‐centre.
Effects of Dislocation Distribution on the Specific Heat of Deformed Type II Superconductors
Authors: Barbee T. W.
Published: July 2007

The effects of dislocation distribution on the mixed state specific heat of deformed Type II superconductors are considered. Calculations based on a simple model are shown to predict behavior in agreement with reported experimental results for deformed niobium if an internal variation for ϰ of 0.4 caused by dislocation distribution is assumed. The implications of this result for fluxoid pinning in deformed Type II superconductors are discussed. Applications of measurements of the mixed state specific heat of Type II superconductors to the study of imperfections and imperfection distribution are also discussed.
Thermal Expansion of Silicon and Zinc Oxide (I)
Authors: Ibach H.
Published: July 2007

A new expansion cell for the three‐terminal capacitance method is developed. Length changes in the order of 10−9 cm can be measured at samples of only 4 mm. At first the expansion coefficient of silicon (reference material) is investigated in detail from 20 to 300 °K. The work is completed by interferometric measurements up to 800 °K. The temperature dependence of the expansion coefficient is discussed using the thermal equation of state. Furthermore conclusions are drawn concerning the contributions of different phonon branches and compared to calculations on the basis of well‐known models.
Infrared Absorption by Localized Vibrations of H− and D− Ions in NaF and LiF Crystals
Authors: Dötsch H.
Published: July 2007

The infrared absorption due to localized vibrations of H− and D− ions in NaF and LiF is measured between 20 and 300 °K. The oscillator strengths are temperature independent. Measurements with uniaxial pressure show that the frequency of the local mode in NaF:H− is shifted by lattice distortions of the symmetry of Γ and Γ but not of Γ. In NaF:D−, LiF:H−, and LiF:D− two‐phonon decays are allowed resulting in relatively large halfwidths at low temperatures. In NaF:H− a two‐phonon decay is not possible and the halfwidth becomes smaller than the minimum spectral slit width of the grating spectrometer. The temperature dependence can be described by a scattering process in NaF:H− and by a composition of a scattering process with a two‐phonon decay process in the other systems. The anharmonic frequency shift is calculated to a first approximation. In a simple density approximation the side band spectra can be described better by anharmonicity than by nonlinear dipole moments.
Stress‐Induced Dichroism in Tl+‐Doped Potassium Halides
Authors: Bimberg D. , Dultz W. , Gebhardt W.
Published: July 2007

Change of absorption under uniaxial compressive stress has been investigated in KCl: Tl+ and KBr: Tl+ on the A‐band and in KI: TI+ on the A‐ and B‐bands at 77 and 20 °K. A. light modulation method has been applied with a rotating polarizer. The data were analysed by the method of moments and show a red shift of the bands with stress and polarization parallel to the [100] axis and a blue shift of the bands with stress and polarization parallel to the [110] axis. From these data it is concluded that the Jahn‐Teller distortion of the Eg mode of the A‐excited state leads to a compression of the impurity octahedron.
Internal Friction in AlAg Alloys
Authors: Schoeck G. , Bisogni E.
Published: July 2007

A study has been made of an internal friction peak which occurs due to the precipitation of the γ′ phase from supersaturated AlAg alloys. From the known crystallographic relations and using electron transmission observation from the literature on the morphology of the precipitates, it is shown that the peak is caused by the diffusion controlled relaxation of partial dislocations surrounding the precipitates.
Capacitance—Voltage Relations of Schottky and p—n Diodes in the Presence of both Shallow and Deep Impurities
Authors: van Opdorp C.
Published: July 2007

If at the lightly doped side of an abrupt junction both shallow and deep impurities of the same kind are present, the slope of a low‐frequency C−2 vs. V plot is proportional to the total concentration of these impurities. The value of the voltage Ve as found by extrapolating C−2 to zero depends on the individual concentrations and depths of the two kinds of impurities. A simple expression for Ve is derived. The same is done for a diffused graded junction with both shallow and deep impurities in the starting material. If the depths of the impurities are known, the two concentrations can be found separately.
Modulation and Excitation of the Infrared Luminescence of ZnS(Cu) by Electric AC Fields
Authors: Gumlich H.‐E. , Moser R. , Neumann E.
Published: July 2007

The infrared luminescence of ZnS(Cu) due to internal transitions within the 3d9 configuration of Cu2+ ions excited by radiation may be modulated by electric ac fields (field modulation). The experimental data lead to the conclusion that the modulation of the emission is caused by field‐induced density oscillations of free electrons within the ZnS lattice. The infrared Cu2+ emission may also be obtained without exciting radiation by the action of the electric ac field (electroluminescence). The infrared electroluminescence may be stimulated or quenched by additional irradiation.
Supertransferred Hyperfine Field for Lu in YbIG
Authors: Wäppling R. , Karlsson E. , Johansson K.
Published: July 2007

A supertransferred hyperfine field and its temperature dependency was observed for a diamagnetic Lu impurity introduced into Yb‐sites in YbIG. The contribution from the Yb sublattice is fairly large and the hyperfine field follows the total magnetization rather than any of the sublattice magnetizations. As intermediate results it has been verified that the electronic ground state of a daughter atom (Lu) of a radioactive decay in an insulating medium is reached in a time short compared to 10−9 s and that the nuclear magnetic moment of the 114 keV state in 175Lu is (1.99 ± 0.15) μN.
Sensitivity of Many‐Beam Electron Microscope Images to the Form of Absorption and Extinction Parameters
Authors: Metherell A. J. F. , Fisher R. M.
Published: July 2007

The sensitivity of electron microscope image intensity profiles to the form of the absorption and extinction parameters has been analyzed for many‐beam diffraction conditions which predominate at high voltage for most metals. The results show that the profiles are most sensitive to the extinction parameter which must be known to better than 5% if good agreement with experiment is to be obtained. It appears that the form of the absorption parameters has little influence on the intensity distributions of n‐beam profiles, especially for medium atomic number elements such as copper.
Volume and Surface Magnon States in Semi‐Infinite Ferromagnetics
Authors: Stojanović S. , Tošić B. S.
Published: July 2007

In this work the theory of surface and volume magnon states in a semi‐infinite ferromagnetic with simple cubic lattice is formulated in the second quantization representation. The volume and surface phonon states as well as the Hamiltonians of the magnon interactions with the volume and surface phonons are also formulated. The probabilities for surface annihilation of volume magnons due to magnon‐phonon interaction are investigated. It is shown that this process is more probable in the case that surface phonons participate in the process.
Nuclear Spin‐Lattice Relaxation in NH4PF6 · NH4F
Authors: Tōdō I. , Tatsuzaki I.
Published: July 2007

Nuclear magnetic resonance spectra and nuclear spin‐lattice relaxation times of 1H and 19F in NH4PF6 · NH4F have been studied. The linewidths of both nuclei did not change between room temperature and 77 °K. No anomaly in the relaxation time of 1H has been found at both phase transition temperatures. However, an anomaly in the relaxation time of T and in the correlation time τF of 19F, which were assumed to be due to the random reorientational motion of the PFion, were found at both phase transition temperatures. — The results suggest that the antiferroelectric phase changes in NH4PF6 · NH4F are accompanied by a change in the lattice structure which alters the potential in which the PFion moves.
Das Flußliniensystem axial magnetisierter zylindrischer Supraleiter zweiter Art
Authors: Essmann U. , Träuble H.
Published: July 2007

Als Grenzfälle der Flußlinienanordnung realer Supraleiter 2. Art mit hohen χ beobachtet man ein regelmäßiges Dreiecksgitter bei hoher Flußliniendichte und eine flüssigkeitähnliche Struktur bei niedriger Flußliniendichte. Infolge der Anwesenheit von strukturellen Inhomogenitäten, wie z. B. Versetzungen, in den Proben hängen die Dichte und die Anordnung der Flußlinien vom Radiusvektor der Proben ab. Die beobachteten Flußgradienten werden diskutiert und versetzungstheoretisch beschrieben. — Die Fehlordung im Flußliniengitter wird mit abnehmender Flußliniendichte größer. Bei den hier untersuchten Pb‐In Proben geht das Flußliniensystem für Bloc < 30 G in eine Flüssigkeitsstruktur über. Diese Erscheinung wird auf die Wechselwirkung der Flußlinien mit Haftstellen im Metallgitter zurückgeführt. Aus den Abständen isolierter Flußlinien vom Rand des Flußliniensystems wird die Haftkraft für einzelne Flußlinien abgeschätzt.
The Electron Microscopic Observation of Mechanical Twins in Gadolinium
Authors: Kumar J. , Srivastava O. N.
Published: July 2007

Mechanical twinning in gadolinium has been observed using an electron microscope. The analysis of electron diffraction patterns revealed that the twinning elements are K1 = K2 = (1012) and η1 = η2 = [1011]. The possible mechanism of genesis for these twins are investigated. It is found that the twins are nucleated due to thermal stresses set up in the films as a result of electron irradiation. There is no evidence for the pole dislocation mechanism to be operative in the present case, instead, the observations suggest that the twin formation is in accordance with the Bell‐Cahn mechanism.
Dislocation Helices in Molybdenum
Authors: Becker C. , Pegel B.
Published: July 2007

Numerous large helical dislocations with lengths up to 4 mm and diameters between 10 and 130 μm have been observed in molybdenum by means of X‐ray topography. From these observations an equilibrium vacancy concentration of about 3 × 10−6 at 2000 °C in molybdenum is derived.
Stage I Recovery of Resistivity in Electron‐Irradiated Silver and Gold. I. Silver
Authors: Wiffen F. W. , Snead C. L. , Kauffman J. W.
Published: July 2007

The stage I recovery of silver has been investigated by resistivity measurements and isochronal annealing of 99.999% purity silver after irradiation with 2.0 MeV electrons at liquid helium temperature. Detailed annealing schedules for several different initial defect concentrations and for a radiation doped run confirmed the general similarity in the stage I recovery behavior of silver and copper and revealed the systematic differences between the two metals. Silver shows several first‐order recovery substages and shows a small component of recovery due to free interstitial migration near 31 °K. The total amount of recovery in stage I was found to be a sensitive function of defect concentration, for small defect concentrations, with the amount of recovery increasing for increasing initial damage over the range investigated. The observed results are explained in terms of a “competitive process, one interstitial model” with most of stage I recovery due to close pair recombination. The fate of freely migrating interstitials is governed by the relative importance of impurity trapping, vacancy annihilation, and interstitial complex formation. The importance of each of these processes depends upon the initial defect concentration, impurity concentration, and the effectiveness of vacancies and interstitials for capturing interstitials. The higher probability of dimer formation in silver than in copper is a result of the larger radius of the interstitial strain field in silver and results in the smaller amount of stage I recovery, the smaller size of IE, and is a major contributor to the observed lack of dose dependence in silver.
Injected Electron Currents Through Insulators
Authors: Christov S. G.
Published: July 2007

The previously presented unified theory of field and thermionic emission is extended to electron emission into dielectrics, including thin films between two metal electrodes. The current equations are derived under the assumption of a parabolic energy—momentum dependence and convenient barrier shape approximations for various thicknesses of the insulating layer, but the general method is used in the case of any arbitrary barrier shape. Both cases of equal and unequal effective electron masses in the insulator and the metals are considered. The current expressions obtained are applicable to the whole range of fields and temperatures between the limits of thermionic and field emission.
Diffusion of Inert Gases in Copper
Authors: Rickers G. , Sørensen G.
Published: July 2007

The ion bombardment technique was used to study inert gas diffusion in polycrystalline copper. Radioactive single charged ions of krypton and xenon were implanted in copper at energies between 20 and 450 keV. The ion‐doped specimens were thermally annealed, and the influence on gas release of implanted ions, implantation energy, and dose was investigated. A new chemical sectioning technique was used to measure the integral distribution of the implanted ions before and after thermal annealing. By correlating the measurements of fractional gas release with those of diffusion profiles, it was possible to obtain a model for inert gas diffusion in copper.
Internal Friction Due to Precipitation
Authors: Schoeck G.
Published: July 2007

Internal friction can be caused by precipitates if they produce internal strains, have elastic moduli different from the matrix or if they have incoherent or semicoherent interface boundaries. By considering the interaction energy with an externally applied stress field, the possible internal friction effects are discussed. It is shown that an internal friction peak can only be caused by interface relaxation in semi‐coherent or incoherent interface boundaries.
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

Dielectric 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

It 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

The 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

The 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

Phonon 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

Term 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

Measurements 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

Electroreflectance 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.
On the Temperature Dependence of Infrared Absorption Lines due to Lattice Vibrational Modes
Authors: Strauch D.
Published: July 2007

A theory is presented which describes the intensity of absorption lines due to infraredactive vibrations and the strength of their side bands. The theory allows for arbitrary anharmonicity and is applicable to perturbed and unperturbed crystals.
ESR Investigation of Ni+ in Illuminated AgCl and AgBr
Authors: Höhne M. , Stasiw M.
Published: July 2007

AgCl‐ 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

The 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

A 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

The 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

Es 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

Measurements 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

Floating‐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

An 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:

equation image

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

The 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

The 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

The 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

The 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

Neutron 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

Ferromagnetic 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

Nous 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

Nous 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

The 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

Highly 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

The 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

The 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

Screw, 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

When 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.
The Compressive Deformation Behavior of Long Range Ordered Polycrystalline iron—aluminum Alloys
Authors: Leamy H. J. , Kayser F. X.
Published: July 2007

The compressive deformation behavior of polycrystalline iron‐aluminum alloys has been investigated (i) at 298°K for specimens heat treated in various ways and containing from 22.0 to 31.7 at% Al, and (ii) from 77 to 655°K for well‐annealed specimens containing 26.6 at% Al. Alloys which possess significant DO3 type long range order exhibit marked composition and temperature dependent variations in deformation behavior. Specifically, those containing ⪆ 27 at% Al exhibit two linear and one parabolic deformation stage at 298°K. The linear stages are shown to be a result of the production and motion of DO3 type superlattice dislocations. The absence of these stages in well‐annealed specimens is attributed to the lack of thermal assistance for the DO3 superlattice dislocation nucleation process. The flow stress levels which characterize the two linear stage behavior agree with calculations of the stress required for production of antiphase boundaries. Results obtained from quenched specimens are in agreement with the above conclusions, and the changes induced by quenching are in accord with calculations of the effect of thermal antiphase boundaries upon dislocation motion.
Infrared Absorption in Gallium Phosphide
Authors: Pikhtin A. N. , Yaskov D. A.
Published: July 2007

An investigation was made on the infrared absorption spectra of gallium phosphide single crystals doped with different impurities in the temperature range from 90 to 420°K. With decreasing temperature a transformation of the absorption spectrum due to interband transitions between conduction band valleys to the absorption spectrum due to impurity states was observed. On the basis of a theoretical analysis of the results obtained, a number of parameters of the GaP band structure and impurity states characteristics have been determined.
Effect of Impurities on the Individual Dislocation Mobility in Silicon
Authors: Erofeev V. N. , Nikitenko V. I. , Osvenskii V. B.
Published: July 2007

An investigation was made of the dependence of individual 60° and screw dislocation velocities on stress, temperature, and impurity (B, As, Sb) concentration in silicon single crystals. It was found that both donor and acceptor impurities result in decrease of the activation energy (U) of the dislocation motion. The donor influence on U is stronger. The possible reasons for the observed phenomenon are analysed in terms of the effect of impurities on the mechanism of overcoming of Peierls stresses by a dislocation.
Elastic Strains during Decomposition of Homogeneous Solid Solutions — Periodic Distribution of Decomposition Products
Authors: Khachaturyan A. G.
Published: July 2007

A decomposition is considered of an elastically anisotropic homogeneous solid solution in two phases having the same structure as that of the original solution. The following assumptions are made: 1. The phases differ in their composition and the specific volume only. 2. The inclusions of precipitating phases are coherent and have the same elastic moduli as those of the matrix. The configuration and inclusion shape is assumed to be determined by minimizing the elastic energy associated with the difference in specific volumes of the phases. A theoretical analysis for the alloys with negative elastic anisotropy leads to the configuration with a minimum of the elastic energy when the inclusions are distributed periodically. In this case the mechanism of the formation of periodic distributions differs considerably from that proposed by Cahn. Three types of metastable periodic distributions are possible, enumerated below in order of increasing elastic energy. Firstly, there is an one‐dimensional distribution representing the system of similar parallel laminated inclusions, regularly spaced along a cubic plane (e.g. (001)). Secondly, there is a two‐dimensional distribution which may be viewed as a planar square macro‐lattice formed by inclusions. The two basic translation vectors lie along the 〈100〉 orthogonal cubic directions. Finally, there is a three‐dimensional distribution, representing a primitive cubic macro‐lattice, the site of which are inclusions of equilibrium phases and of the partially decomposed matrix.
Franz‐Keldysh Effect on Indirect Transitions in GaP
Authors: Gasakov O. , Nasledov D. N. , Slobodchikov S. V.
Published: July 2007

The change of the spectral photosensitivity of GaP p‐n junctions with electric field has been investigated. The Franz‐Keldysh effect on indirect Γ15v → X1, Γ15v → X3 transitions has been found. The Γ15v → X1 transitions involve emission and the absorption of TA (Eph = 0.013 eV) and LA (Eph = 0.035 eV) phonons, the Γ15v → X3 emission and the absorption of TO phonons (Eph = 0.047 eV). The value of EΓ15v → X3 amounts to 2.630 eV and that of EΔ to 0.37 eV.
Some Factors Influencing the Visibility of Dislocations in Transmission Electron Microscopy
Authors: Loretto M. H. , France L. K.
Published: July 2007

An investigation has been made into the degree of deviation (sg) from the Bragg conditions required to make dislocations (of Burgers vector b) effectively invisible for a variety of diffracting vectors (g) when the condition g ± b = ± 1 obtains. It is found that these values of sg decrease as the magnitude of g increases, thus making confusion of the g · b = = ± 1 and g · b = 0 cases more likely for large values of g.
The Phase Transition in CsCl Mixed with CsBr, RbCl, and KCl
Authors: Weijma H. , Arends J.
Published: July 2007

The phase trans tion in single crystals of CsCl mixed with CsBr, RbCl, and KCl was investigated by means of ionic conductivity measurements and differential thermal analysis. Adding RbCl or KCl to CsCl reduces both the transition temperature, Ttr, and the enthalpy of transformation, ΔHtr. In the system CsClCsBr Ttr shifts to higher values relative to that of pure CsCl, whereas ΔHtr decreases considerably. A thermodynamical consideration of the phase transition temperatures in the CsClCsBr system shows that pure CsBr should exhibit a transition from the B2 to the B1 structure at 880 °C with an enthalpy variation of (300 ± 100) cal/mol. From the DTA experiments one should expect an enthalpy of (100 ± 50) cal/mol for the transformation of pure CsBr.
Quenching Experiments with High‐Purity Iron
Authors: Glaeser W. , Wever H.
Published: July 2007

Iron wire of very high purity was quenched in a helium cryostat. Changes in electrical resistivity were used to measure the recovery during isochronal and isothermal annealing in the temperature range 4.2 to 1000 °K. Two sharp recovery stages were observed (first stage: 300 °K < T < 400 °K, second stage: 400 °K < T < 520 °K). The activation energy was determined by the change in slope and the Meechan‐Brinkman test (first stage: 0.48 to 0.51 eV, second stage: 1.05 to 1.1 eV). Both recovery processes follow a first‐order kinetic law. These two stages are observed after cold work as well. The first stage is attributed to the migration of carbon atoms alone and paired with vacancies, the second stage corresponds to the migration of vacancies. The recovery spectrum exhibits in three different temperature ranges a resistivity increase and a final recovery stage in the range 850 to 1000 °K. The last increase and recovery stage may be due either to the redissolution of carbon atoms or to Bloch wall motion.
Effect of High Pressure on the Energy Gap of Indium and Thallium Superconducting Films
Authors: Galkin A. A. , Svistunov V. M. , Dikii A. P.
Published: July 2007

The effect of high pressure (up to 15000 atm) on the energy gap of In and Tl superconducting films was investigated by the tunnel effect on superconductor–barrier–superconductor systems. As directly found in the experiments, the In values 2 Δ/kTc indicate a reduction of the electron–phonon interaction under pressure for this metal. In the range up to 8 katm the value 2 Δ/kTc for Tl remained constant within the experimental error and was found to be 3.64 ± 0.06.