bluuebunny/crossref_metadata_2025 huggingface dataset:
Charge of Dislocations in Pure and γ‐Irradiated LiF
Authors: Rueda F. , Dekeyser W.
Published: July 2007

The electrical charge of newly created dislocations in non‐irradiated and γ‐irradiated LiF is studied by the indentation method. In both cases the dislocations are negatively charged. Subsequent annealing after irradiation produces a reversal of sign of that charge, the first isoelectric temperature being located in the range of bleaching of F‐ and M‐centres. These effects are attributed to negative vacancies produced by irradiation and thermal bleaching.
Theorie des Dielektrizitätstensors in Relaxationszeit‐Approximation
Authors: Mertsching J.
Published: July 2007

Im Rahmen der “random phase approximation” wird mit Hilfe des statistischen Operators der Elektronen die Stromdichte berechnet, die durch ein elektromagnetisches Feld in einem Festkörper induziert wird. Dabei wird in der Bewegungsgleichung für den statistischen Operator der Stoßterm durch ein Relaxationsglied approximiert und die Gleichgewichtsverteilung derart gewählt, daß Stromdichte und Ladungsdichte eichinvariant sind und der Kontinuitätsgleichung genügen. Aus der induzierten Stromdichte lassen sich der komplexe Dielektrizitäts‐ und Permeabilitätstensor für beliebige Wellenvektoren q und Frequenzen ω, wenn auch bezüglich der transversalen Komponenten im allgemeinen nicht völlig eindeutig, bestimmen. Im Grenzfall q → 0 ist der Dielektrizitätstensor ϵ(ω) eindeutig bestimmt und setzt sich aus dem Intraband‐Drude‐Term sowie Interbandtermen zusammen, die verglichen mit den von Ehrenreich und Philipp 1962 angegebenen den zusätzlichen Faktor (1 + magnified image) enthalten, wobei τνν′ eine Interband‐Relaxationszeit ist.
Diffusion von Sn und Zn in Sn und in einer homogenen Sn‐Zn‐Legierung
Authors: Bergner D. , Lange W.
Published: July 2007

Neben Ergebnissen methodischer Untersuchungen über die Anwendbarkeit der Fisherschen Methode zur Messung von Korngrenzendiffusionskoeffizienten werden die Ergebnisse von Messungen der Volumendiffusion von Sn und Zn und der Korngrenzendiffusion von Sn in Sn und in einer homogenen Sn‐Zn‐Legierung mit 0,5 Gew.% Zn mitgeteilt.
Twinning deformation in iron at 4 °K
Authors: McRickard S. B.
Published: July 2007

Fine grained, Ferrovac iron has been found to deform in a discontinuous manner when tested in tension at 4.2 °K. The deformation has been found to be a unique continuous twinning process which is initiated by a critical stress of 137000 psi and from which a uniform strain energy release of 0.01 eV/mol for each twinning event has been calculated. The characteristics of this twinning deformation are discussed and comparisons with other reported low temperature phenomena are made.
Zum linearen Anklingen der Photoleitfähigkeit in Halbleitern
Authors: Egorov V. D.
Published: July 2007

Es wird der Einfluß der Oberflächenrekombination und einer parasitären Kapazität auf den Anfangsteil des Anklingens des Photosignals betrachtet. Die Ergebnisse ermöglichen Aussagen über die Verwendbarkeit eines Germanium‐Photowiderstandes zur Messung der Intensität von Lichtimpulsen.
Radiation‐induced point defect clusters in copper and gold
Authors: Merkle K. L.
Published: July 2007

The transmission electron microscope technique was used to investigate the defect structures introduced by bombardment of thin films of copper and gold with heavy particles. The black spot defects in gold can be shown to be produced directly in displacement cascades if the energies of the cascades are high enough. The size of the observed defect clusters increases with increasing primary energy. A very energetic primary can produce a bunch of closely spaced defect clusters. Charged particle irradiations of copper indicate that contrary to gold not every primary event above a certain threshold energy is observed. This is interpreted as being due to the formation of non‐overlapping subcascades, each of which might form a stable cluster but is generally too small to be observed under our experimental conditions. Those clusters in copper and gold that have been identified unambiguously are of vacancy type.
Radiation damage and xenon release in quartz and fused silica following ion bombardment
Authors: Matzke Hj.
Published: July 2007

Single‐crystalline quartz and fused silica were bombarded with 40 keV xenon ions to give integrated ion doses of up to 2 × 1016 ions/cm2. At low dose (8 × 1010 ions/cm2) diffusional release processes dominated with activation enthalpies of 58 and 61 kcal/mol for quartz (diffusion along and perpendicular to the c‐axis respectively) and 72 kcal/mol for fused silica. Diffusion in the amorphous phase was markedly slower than diffusion in the crystalline phase. At doses ≧ 4 × 1013 ions/cm2 radiation damage in the form of a phase change to a quasi‐amorphous state occurred in quartz, as revealed by reflection electron diffraction. The annealing of this structural damage coincided with enhanced thermally activated gas release at temperatures below those of volume diffusion. Fused silica showed a similar enhanced release at high bombardment dose. Thus, the quasi‐amorphous phase produced by ion bombardment is different from that of fused silica. The present results indicate further, in agreement with the literature on neutron irradiated quartz and fused silica, that both materials approach a common state at a high level of radiation damage.
Strahleninduzierte Phasenumwandlungen einiger Substanzen des Perowskit‐Gittertyps und ihre thermodynamische Behandlung
Authors: Hauser O. , Schenk M.
Published: July 2007

Es werden experimentelle Ergebnisse über die thermischen und strahleninduzierten Phasenumwandlungen sowie über die Verschiebung der Umwandlungstemperaturen zwischen den Raum‐ und Hochtemperaturphasen von BaTiO3, PbZrO3 und PbTiO3 bekanntgegeben. Es wurden vorwiegend röntgenographische und kalorimetrische Untersuchungen durchgeführt. Für die Deutung der erzielten Ergebnisse werden strukturelle und thermodynamische Überlegungen herangezogen. Dabei zeigt sich, daß die strahleninduzierten und thermischen Phasenumwandlungen im Rahmen einer thermodynamischen Betrachtungsweise gemeinsam behandelt werden können.
Über den Begriff „aktives Gleitvolumen”︁ und dessen Bedeutung
Authors: Schwink Ch.
Published: July 2007

Der Begriff „aktives Gleitvolumen”︁ bzw. „aktive Kristallänge”︁ wird in die Plastizitätslehre eingeführt. Er spielt eine wesentliche Rolle, wenn das aktive Gleitvolumen von den äußeren Verformungsparametern, Geschwindigkeit und Temperatur, abhängt. Das ist im allgemeinen dann zu erwarten, wenn Gleitvorgänge thermisch aktiviert ablaufen. Aus einer energetischen Überlegung wird eine Näherungsformel für die Abhängigkeit des aktiven Gleitvolumens von der Abgleitgeschwindigkeit gewonnen. Sie beschreibt die bisher vorliegenden experimentellen Ergebnisse. Folgerungen für die Analyse thermisch aktivierter Vorgänge, die sich aus der Veränderlichkeit des aktiven Gleitvolumens ergeben, werden kurz besprochen.
Colour centres in KCl doped with Zn+2, Cd+2, and Hg+2
Authors: Ben‐Dor L. , Glasner A. , Zolotov S.
Published: July 2007

The absorption spectra of additively coloured Zn+2, Cd+2 and Hg+2 doped KCl indicate the formation of monovalent as well as neutral atomic centres. The formation of these centres follows the trapping of electrons by the metal ions added to the KCl.
Elektronenmikroskopische Oberflächen‐ und Durchstrahlungsuntersuchungen von Eisen‐Einkristallen sowie der Einfluß der Orientierung auf deren Verfestigungsverhalten
Authors: Bilger H.
Published: July 2007

Die Verfestigungskurven mittelorientierter Eisen‐Einkristalle können durch 3 Verfestigungsbereiche charakterisiert werden. Oberflächenbeobachtungen lassen im Bereich I überwiegend Einfachgleitung, im Bereich II Mehrfachgleitung erkennen. Die Laufwege der Schraubenversetzungen sind in beiden Bereichen kleiner als diejenigen der Stufenversetzungen. Im Bereich III findet die Abgleitung innerhalb welliger Gleitbänder statt. Die von Beginn an starke Verfestigung randorientierter Kristalle wird durch Mehrfachgleitung verursacht.
Study of energy transfer from 3d to 4f electrons in antiferromagnetic MnF2: Eu3+ crystals
Authors: Eremenko V. V. , Matyushkin E. V. , Petrov S. V.
Published: July 2007

The spectrum and luminescence intensity of the antiferromagnetic crystals MnF2:Eu3+ are investigated experimentally for temperatures between 20 and 90 °K. This range includes the magnetic ordering temperature TN (≈ 68 °K). At the temperature TH (≈ 0,5 TN), corresponding to the spin ordering of the excited Mn2+ ions, the luminescence intensity due to these ions shows a sudden increase while the luminescence intensity due to the Eu3+ ions suffers a sudden decrease. This indicates that an anomalous change occurs in the transfer of energy between the Mn2+ and Eu2+ ions due to the condensation of the local magnetic vibrations of the optically excited Mn2+ ions.
Solution hardening in niobium
Authors: Harris B.
Published: July 2007

A study has been made of the solution hardening of niobium by tantalum, vanadium, zirconium, and tungsten. It is found that hardening is linear with composition at small concentrations and is simply related to the sum of the atomic size and elastic modulus differences. Agreement with the solution‐hardening model of Fleischer for f.c.c. metals is not exact, however, for the results indicate that the atomic size mismatch, rather than the elastic modulus difference, is the dominant factor in hardening. – Strain‐hardening, strain‐rate sensitivity, and temperature dependence of the flow‐stress are studied, and it is shown that the basic deformation mechanism remains unaltered by solute additions. It is suggested that the solutes raise the long‐range, athermal component of the flow‐stress and reduce the short‐range, thermally‐activated component.
Kriechexperimente an hochreinen Kupfer‐Einkristallen
Authors: Schmid G.
Published: July 2007

Nach der Methode der stufenweisen Belastung wurden Kupfer‐Einkristalle mit der Reinheit 99,999% bei 78 °K und bei Zimmertemperatur verformt. Neben dem zeitlichen Kriechgesetz wurde auch die Abhängigkeit der Abgleitgeschwindigkeit von der Temperatur und der Schubspannung mit Hilfe von Temperatur‐ und Lastwechseln gemessen. Die nach Schoeck durchgeführte Analyse der thermisch aktivierten Prozesse zwingt zu der Annahme, daß die Versetzungen häufig Rücksprünge ausführen und daß ein Spektrum von Hindernissen vorliegt. Aus dem Aktivierungsvolumen und der freien Aktivierungsenthalpie lassen sich die Versetzungsdichten in Abhängigkeit von der Verformung abschätzen. Der Vergleich mit den elektronenmikroskopisch gewonnenen Werten von Eßmann liefert eine recht befriedigende Übereinstimmung und zeigt, daß das Schneiden der Waldversetzungen geschwindigkeitsbestimmend ist.
Calculation of the mean inner potential of a crystal in the statistical theory
Authors: Anishchenko R. I.
Published: July 2007

The mean inner potential of a crystal is calculated for 49 different metals by using the Thomas‐Fermi‐Dirac model of a compressed atom. The dependence of the mean inner potential on the atomic number Z has a distinctly periodic character. The effect of the exchange interaction and the conduction electrons on the potential are taken into account. A comparison with experimental data shows good agreement for the heavy elements.
Adiabatic, Isothermal, and Intermediate Pressure Derivatives of the Elastic Constants for Cubic Symmetry. II. Numerical Results for 25 Materials
Authors: Barsch G. R. , Chang Z. P.
Published: July 2007

The purely adiabatic and the purely isothermal pressure derivatives of the elastic constants are calculated from the experimentally determined mixed isothermal‐adiabatic pressure coefficients of the elastic constants for 24 cubic crystals and one isotropic material. Also the linear combinations of the third‐order elastic constants that can be determined from these data are given for the different thermodynamic conditions. The first two expansion coeffcients of the volume versus pressure relation were determined from the ultrasonically measured elastic constants and their pressure coefficients and compared with Bridgman's high pressure volumetric data.
Vacuum Heat Treatment of CdS Single Crystals
Authors: Böer K. W. , Kennedy C. A.
Published: July 2007

Changes of the spectral distribution of photoconductance and conductance glow curves after heat treatment between 370 and 620°K and immediate quenching of undoped CdS single crystal platelets in ultrahigh vacuo are described. After annealing, the electrical properties after heat‐treatment quenching sequences are largely reproducible. The results are interpreted as the dissociation of larger defect associates containing Cd vacancies and consequent production of single Cd vacancies causing a trap level at Ec – Et ≈︁ 0.4 eV and vacancy pairs with trap levels at Ec – Et ≈︁ 0.95 eV. Dissociation and stress enhanced diffusion of vacancies in the neighborhood of associates becomes noticeable at treatment temperatures above 350°K.
On the Scattering Processes in Semiconductors
Authors: Kołodziejczak J.
Published: July 2007

The scattering processes in semiconductors are analysed for the purpose of the solution of a non‐linear Boltzmann equation. The collision term in the Boltzmann equation is calculated for acoustic modes, and for polar and non‐polar optical modes. The differential collision operators are obtained for the isotropic part of the distribution function. The calculations are carried out assuming possible nonparabolicity of the energy band.
Messung von Versetzungsgeschwindigkeiten in Germanium
Authors: Schäfer S.
Published: July 2007

Die Versetzungsgeschwindigkeit in Ge wird an Halbringen gemessen, deren Durchstoßpunkte an der Oberfläche mit einem Ätzmittel sichtbar gemacht werden. In der Nähe des einen Durchstoßpunktes hat der Versetzungshalbring Schrauben‐, in der Nähe des anderen 60°‐Charakter. Die Halbringe sind nicht stabil und können nur mit Hilfe einer Vorspannung in ihrer Ausgangslage gehalten werden. Die Versetzungsgeschwindigkeit wurde zwischen 220 und 580°C gemessen und hängt von der Temperatur T und der Spannung τ wie \documentclass{article}\pagestyle{empty}\begin{document}$ v = B_n \left({\frac{\tau }{{\tau _0 }}} \right)^m {\rm exp}\left({ - \frac{Q}{{kT}}} \right)$\end{document} ab. Es ist Q = 1,62 eV für Schrauben‐ und 60°‐Versetzungen; m ergibt sich zu 1,0 für Schraubenversetzungen und zu 1,2 für 60°‐Versetzungen‐Ferner ist Bn = 108 mm/s und τ0 = 1 kp/mm2.
On the Theory of Galvanomagnetic Phenomena in Strong Electric Fields
Authors: Kolodziejczak J.
Published: July 2007

Some galvanomagnetic effects are calculated for electric fields which are sufficiently high to give quadrac tideviations from Ohm's law. The calculations are carried out assuming nonparabolicity of the energy band. Acoustic mode scattering, and polar and non‐polar optical mode scattering are included in the analysis. Kane's model of the nonparabolic band is used in the final result.
Dependence of the Ion–Electron Emission Coefficient on the Angle of Incidence
Authors: Evdokimov I. N. , Mashkova E. S. , Molchanov V. A. , Odintsov D. D.
Published: July 2007

The dependence of the ion‐electron emission coefficient on the angle of incidence is studied for targets of polycrystalline metals (Cu, Ag, Mo, Zr, W, Bi), and a graphite target, bombarded with 25 to 30 keV noble gas and nitrogen ions. The application of a magnetic field parallel to the axis of rotation shows that both the positive and negative ion currents to the collector are negligibly small. The emission coefficient increases as the angle of incidence increases up to angles of about 80 to 85°. Up to a certain limiting angle (from 36 to 81° for different ion‐target combinations) the angular dependence may be approximated by a reciprocal cosine law, while for larger angles the variation is rather slower. Comparisons are made, calculations based on the transparency model.
Microstrain Region and Transition to Macrostrain in 99.9% Polycrystalline Copper
Authors: Man J. , Holzmann M. , Vlach B.
Published: July 2007

A study is made of the effect of grain size and substructure on the microstrain region and on the transition to the macrostrain region. The results do not agree with the conclusions obtained from the Brown‐Lukens theory. The possibility of using statistical theory to describe the stress‐strain dependences in the microstrain region is considered.
Photochemical Properties of SH− Ions in KCl and KBr Crystals
Authors: Facey O. E. , Jacobs P. W. M.
Published: July 2007

The photochemistry of KCl and KBr containing SH− impurity ions has been investigated. In addition to the formation of S− and U2‐centres reported previously, U‐centres are formed in high yield and F‐centres in low yield. The thermal contribution to the photochemical process is slight (≈︁ 0.013 eV). The kinetics of the decay of U2‐centres has been shown to be bimolecular and to correspond mainly to the reaction S− + Hi → SH−, where Hi denotes an interstitial hydrogen atom. A model involving the utilization of the thermal energy released during a radiationless transition from the excited state is successfully used to give a qualitative explanation of the data.
Clustering of Defects in Neutron‐Irradiated Beryllium Oxide
Authors: Rau R. C. , Chase G. A.
Published: July 2007

Transmission electron microscopy and X‐ray diffraction have been combined to study clustering of defects in BeO irradiated to neutron dosages ranging from 0.5 to 11.7×1020 nvt at pile ambient temperature (≈︁ 100°C). Dot clusters which form in the microstructure at dosages greater than about 1.0×1020 nvt are interpreted as being small interstitial loops, oriented on basal planes. X‐ray diffraction patterns contain duplex peaks consisting of sharp components, which reflect changes in the bulk lattice, and broad components which are related to the basal clusters. The observations are consistent with a model containing interstitial basal clusters and random point interstitials, but do not necessarily rule out the presence of point vacancies.
On the Superstructures of Ta2O5 and Nb2O5
Authors: Spyridelis J. , Delavignette P. , Amelinckx S.
Published: July 2007

The superstructures of tantalum and niobium pentoxide are studied. The observations made support the assumption that these, and related crystals, have a “shear structure” and that this shear structure can be observed directly. It is shown that the size of the unit cell depends on the exact stoichiometry of the compound. A model is proposed which explains both the details of the diffraction pattern and the geometry of the line system.
The Lattice Vibrations of Nickel in Krebs's Model
Authors: Shukla M. M. , Dayal B.
Published: July 2007

The vibration spectrum of nickel is studied using Krebs's model. The phonon dispersion curves for the three symmetry directions [100], [110], and [111] are presented and are found to be in very good agreement with neutron scattering measurements. Good agreement is also obtained with the curve of θ against T. The computed G(v) curve is compared with the experimental curves and some agreement is found.
Lattice Dynamics of Solid Adamantane
Authors: Stockmeyer R. , Stiller H. H.
Published: July 2007

The frequency distributions of the translational and rotational motions of H‐atoms in C10H16 and their corresponding amplitudes are determined by means of neutron time‐of‐flight spectroscopy for several temperatures. An estimate of the frequency distribution for the low temperature phase with the statement of James and Keenan (octopole‐octopole interactions) leads to an agreement with the experimental results.
Spin‐Orbit Splitting of the Valence Band of Wurtzite Type Crystals
Authors: Gutsche E. , Jahne E.
Published: July 2007

A 12×12 representation is given of the valence band Hamiltonian at k = 0 which includes the spin‐orbit interaction. Expressions are derived for the energies and the linear combinations of the wave functions for the Γ7, Γ8, and Γ9 subbands. The whole valence band is completely determined by eight parameters: three energies, two parameters coupling states of equal spin, and three parameters coupling states of opposite spin. In principle, all parameters can be obtained experimentally from the energy separations and oscillator strengths for interband transitions for polarization ⟂ c and ∥ c. Anisotropic spin‐orbit interaction and mixing of states originating from the two anions per unit cell are discussed.
Absorption and Dispersion of Light by Molecular Excitons
Authors: Davydov A. S. , Myasnikov E. N.
Published: July 2007

A calculation is made of the real and imaginary parts of the dielectric permeability of molecular crystals due to exciton states, using retarded Green's functions. The interaction of excitons with acoustic and optical phonons is taken into account at different temperatures of the crystal. The dependence of the optical refractive index and the damping coefficient on the frequency of the incident light is obtained in the region of the exciton bands.
Electrical and Photovoltaic Properties of PbSSi Heterodiodes
Authors: Sigmund H. , Berchtold K.
Published: July 2007

The electrical and photo‐electrical properties of PbS‐Si heterodiodes are investigated. The PbS films are grown on Si by a water‐solution reaction at room temperature. The forward and reverse characteristic is similar to that for other heterojunctions (recombination‐tunneling mechanism). The spectral response is in the wavelength range 1 to 3 μm at room temperature. The sensibility in the PbS peak is about 6 × 103 V/W.
Calculation of the Specific Surface Energies of Crystal Planes by Investigating the Orientation of Crystal Nuclei on Inert Substrates
Authors: Pangarov N. A.
Published: July 2007

On the basis of the Stranski‐Kaischew method of the average works of separation, a method is presented for calculating the specific surface energies of crystal planes by investigating the axes of prefered orientation during crystallization on inert substrates. This method is applicable both to crystallization from the gaseous phase and to metal electro‐deposition. The method is applied to the electro‐deposition of silver, and the values of the specific surface energies for the (111), (100), and (110) planes are calculated.
Mikromagnetische Behandlung der Wechselwirkung zwischen Versetzungen und ebenen Blochwänden. I. Allgemeine Theorie
Authors: Pfeffer K.‐H.
Published: July 2007

Infolge der inneren Spannungen, die von den Versetzungen hervorgerufen werden, wird der Magnetisierungsverlauf innerhalb und außerhalb einer Blochwand modifiziert. Für das Gesamtsystem Versetzung‐Blochwand werden durch Minimalisierung der Gesamtenergie die mikromagnetischen Gleichungen in linearisierter Form abgeleitet, wobei die magneto‐elastische Kopplung in Voigtscher Näherung behandelt wird. Die linearen Differentialgleichungen besitzen im Unterschied zu den Gleichungen, die in der Theorie der Einmündung in die ferromagnetische Sättigung auftreten. Koeffizienten, die von dem Magnetisierungsverlauf der ungestörten Blochwand abhängig sind. Zur Lösung derselben wird das Differentialgleichungssystem entsprechend dem nicht‐lokalen Charakter des magnetischen Streufeldes in ein System von zwei linearen, inhomogenen Integralgleichungen übergeführt. In der zugrunde gelegten linearen Näherung ergibt sich die Energieänderung, die mit der Änderung der Magnetiaierungsverteilung verknüpft ist, als die Hälfte der hiermit verbundenen Änderung der magnetoelastischen Kopplungsenergie. Aus der Struktur der magnetoelastischen Kopplungsenergie werden qualitative Aussagen über die Magnetisierungsverteilung und das hieraus resultierende Wechselwirkungspotential im System Blochwand–Versetzung abgeleitet.
Effets de la desaimantation thermique sur les cycles d'hystérésis
Authors: van Dang N.
Published: July 2007

Un échantillon ferromagnétique désaimanté thermiquement pouis soumis à des cycles d'hystérésis symétriques d'amplitude ±HA présente un curieux effet de bascule tres différent des phénomènes de reptation et de bascule positive ou négative déjà connus par de nombreux chercheurs travaillant sur l'hystérésis. On a étudié systématiquement ce phénomène et comparé les données expérimentales avec le schéma de Néel‐Preisach.
Some Relations for Straight Dislocations
Authors: de Wit R.
Published: July 2007

Expressions are presented for the stress, strain, dilatation, and displacement due to an infinitely long straight dislocation, as well as the force per unit length and the total force on a straight dislocation due to another infinite straight dislocation. They differ from previous expressions in the literature in that they are given completely in tensor or vector notation. They are limited to the case of a linear, isotropic, infinite continuum.
Optical and Photoconductive Phenomena in Cuprous Oxide
Authors: Spyridelis J. , Stoimenos J. , Economou N.
Published: July 2007

The optical absorption of cuprous oxide is affected by the defect structure and this is most pronounced in the middle of the stability range, indicating that the observed absorption bands are due to aggregates of vacancies. A simultaneous measurement of the photoconductivity leads to a direct relationship between the exciton stimulated photoresponse and the defect structure.
The Model Potential for Systems with Closed Shells
Authors: Abarenkov I. V. , Antonova I. M.
Published: July 2007

The pseudo‐potential is set up for the Cauchy problem of the Hartree‐Fock equation for an extra electron outside of an atomic system with closed shells. As an approximation to this potential a “model” potential is set up and the method of its determination is developed. The results of calculations for Na+ and Cl− ions are given. The quality of the approximation of the model potential is discussed. The model potential can be applied to the calculation of the valence electron in ionic crystals.
Noncentral Force Model for Hexagonal Close‐Packed Crystal Lattices
Authors: Metzbower E. A.
Published: July 2007

A Born‐von Karman model of the hexagonal close‐packed lattice was considered using a combination of central and angular forces between various sets of neighbors. The interactions between nearest neighbors in the plane were regarded as central forces while the interactions between nearest neighbors out of the plane and next nearest neighbors out of the plane were considered to be noncentral, i.e. both central and angular. Three materials with different axial (c/a) ratios were considered: beryllium (1.568), magnesium (1.624), and zinc (1.855). The equations of motions were evolved and the force constants were related to the elastic constants of the material. The eigenvalues of the secular equation were solved for one hundred twenty one (121) points in that portion of the Brillouin zone irreducible under symmetry operations. The frequency spectrum for each material was obtained from these eigenvalues. The temperature dependence of the specific heat of each material was calculated using the appropriate frequency distribution function. The Debye characteristic temperature and the Einstein characteristic temperature were also obtained as a function of temperature.
The Orientation and Shape of θ Precipitates Formed in an AlCu Alloy
Authors: Vaughan D. , Silcock J. M.
Published: July 2007

Several new orientation groups have been observed for θ precipitates in an Al‐4% Cu alloy. All orientations so far known for θ in relation to both θ′ and the aluminium matrix are summarised. There are 159 known possible orientations for a θ particle relative to the aluminium matrix. Details of the matching interfaces and some of the factors governing nucleation and growth of θ particles are discussed.
X‐Ray Diffraction and Magnetic Studies of Solid Solutions Bi1−xCaxMnO3
Authors: Bokov V. A. , Grigoryan N. A. , Bryzhina M. F.
Published: July 2007

Solid solutions with the general formula Bi1–xCaxMnO3 (0.2 ≦ x ≦ 1) are found to possess the perovskite structure. The phase diagram based on X‐ray diffraction studies involving cubic, orthorhombic and monoclinic modifications is constructed. It is concluded from conductivity and X‐ray data that the transition into the monoclinic II modification is connected with some type of electron ordering on manganese ions. The changes in the paramagnetic Curie temperature resulting from these structural transitions are discussed. The magnetic ordering occurring in the system at about 110 °K can be explained if Zener's double exchange interaction Mn3+‐O2−‐Mn4+ is assumed to occur only in modifications in which electron ordering does not exist. The antiferromagnetic exchange interaction Mn4+‐O2−‐Mn4+ and the weak exchange interaction Mn3+‐O2−‐Mn3+ (the latter being ferromagnetic at a > 3.8 Å or antiferromagnetic at a < 3.8 Å) are proved to be responsible for ferromagnetism in the range 0.2 ≦ x < 0.4, antiferromagnetism in the range 0.4 ≦ x ≦ 0.8 and weak ferromagnetism in the range 0.8 < x ≦ 1.
Exciton Absorption in Doped Germanium
Authors: Asnin V. M. , Rogachev A. A.
Published: July 2007

A study is made of the variation in the shape of the direct absorption edge in germanium with doping level. Increasing the impurity density leads to a broadening and disappearance (at a concentration of about 1016 cm−3) of the direct exciton maximum as well as affecting the shape of the absorption spectrum near the edge.
Valence Band Structure of Wurtzite Type Crystals
Authors: Jahne E. , Gutsche E.
Published: July 2007

The valence band structure of wurtzite type materials is investigated using a k · p approximation. The E(k) dependence for the bands A, B, and C is completely determined by six parameters: two for k ∥ c, three for k⟂c and one additional parameter for a general direction. Relationships between the effective masses at k = 0 are given for the three bands. Even near k = 0 the sub‐bands are strongly non‐parabolic. The constant‐energy surfaces retain their rotational symmetry. Numerically calculated E(k) curves are presented for k ∥ c and k ⟂ c for CdS and CdSe.
Magnetic Field Dependence of Current Oscillations in Piezoelectric Semiconductors
Authors: Hervouet C.
Published: July 2007

Current oscillations are observed in various piezoelectric semiconductors when an electric field, applied in a piezoelectrically active direction, exceeds a certain critical value. The threshold field and the current minimum are decreased by a transverse magnetic field which increases the piezoelectric amplification. This phenomenon is studied theoretically using Spector's model for all values of the magnetic field. There is good agreement between theory and experiment for materials with a low value of σ τ (σ is the conductivity and τ the relaxation time of carriers) but only qualitative agreement for materials with a high value of σ τ because of the classical limit of the theory.
On the Quasi‐Harmonic Theory of Phonons
Authors: Ishikawa K.
Published: July 2007

The shift of phonon frequencies in anharmonic crystals is calculated self‐consistently by a canonical transformation equivalent to Cowley's quasi‐harmonic approximation. The damping of phonons is obtained from the phonon kinetic equations in the above approximation.
Optical Observation of Domain Motion in Ferroelectric BaTiO3
Authors: Kobayashi J.
Published: July 2007

Microscopic observations are made of a BaTiO3 crystal cut in parallel to the ferroelectric axis. Besides nucleating and forward growth of antiparallel domains, sidewards motion of the expanding domains is clearly observed. The fine structure of a nucleating domain is found to consist of a pair of bright stripes in the microscopic view at the point of extinction. The visibility of the antiparallel domains is explained.
A Note on the Consistency of Values of the Spontaneous or Saturation Magnetization of Polycrystalline Iron and Nickel at 298 °K
Authors: Arajs S. , Dunmyre G. R.
Published: July 2007

Mass magnetization of polycrystalline iron and nickel, σ(Hi, 298 °K), where Hi is the internal magnetic field, has been studied by means of a vibrating sample magnetometer at 298 °K using spherical samples. An absolute technique, based on the soft magnetic nature of iron, has been used to calibrate the magnetometer. The spontaneous magnetization, determined by the [σ(Hi, 298 °K)]2 vs. σ(Hi, 298 °K)/Hi technique, is found to be (217.1 ± 0.2) G cm3 g−1 for iron and (55.07 ± 0.11) G cm3 g−1 for nickel. The ratio of these two quantities is in excellent agreement with the corresponding ratio of the saturation magnetizations at 288 °K determined by Danan [2] but not with that reported by Weiss and Forrer [1].
Nuclear Quadrupole Interaction of 23Na and 11B and the Crystal Structure of NaBF4
Authors: Weiss Al. , Zohner K.
Published: July 2007

The nuclear quadrupole interaction of 23Na and 11B in NaBF4 is investigated between 23 and 260 °C using single crystals and crystalline powder respectively. At 23 °C the following results are found: e2 q Q/h (23Na) = 1008.4kHz; e2 q Q/h (11B) = 59.9 kHz; η (Na) = 0.095; η (B) = 0.65. The crystal structure is as follows: Space group Cmcm; a = 6.841 Å, b = 6.266 Å, c = 6.799 Å; Z = 4; Na and B in (4c) with y (Na) = 0.656; y (B) = 0.161; F(I) in (8 f) with y = 0.290; z = 0.086; F(II) in (8 g) with x = 0.163; y = 0.032. The point charge model, NMR‐investigation and the crystal structure agree well assuming a 55% ionic character for the B‐F bond. The high temperature phase of NaBF4 (between 250 and 260 °C) has non‐cubic point symmetry of the B: e2 q Q/h (11B) = 34 kHz.
Einfluß der Nahordnung um Magnesiumverunreinigungen in Wismutschmelzen auf die Kernresonanzfluoreszenz‐Ausbeute
Authors: Holtmeyer G. , Kalus J.
Published: July 2007

Es wurden Kernresonanzfluoreszenz‐(KRF‐)Untersuchungen als Streuexperiment an Mg24 durchgeführt, das als Verunreinigung in Bi eingebaut war. Bei Anhebung der Quellen‐temperatur von Raumtemperatur bis knapp über den Bi‐Schmelzpunkt (300 °C) änderte sich die KRF‐Ausbeute nicht, bei hohen Temperaturen (800 °C) trat eine starke Zunahme um 50% ein. Es wird ein Hartkugelmodell für Schmelzen entwickelt, das diese Zunahme durch Veränderung der Bi‐Nahordnung um die Mg‐Kerne zu deuten versucht.
Threshold Energy for Atomic Displacement in Cadmium Telluride
Authors: Bryant F. J. , Webster E.
Published: July 2007

A study of the luminescence emission spectrum of cadmium telluride at 77 °K before and after bombardment with monoenergetic electrons in the energy range 100 to 400 keV has been made. Enhancement of the luminescence emission band at 1.13 μm after radiation damage of p‐type cadmium telluride permits the measurement of an energy threshold at 340 keV. This is an energy threshold for the production of primary damage in the crystal. An electron of 340 keV energy could transfer a maximum of 7.8 eV to a tellurium atom or 8.9 eV to a cadmium atom. The damage causing the enhancement of the 1.13 μm luminescence emission band is found to anneal completely in a single stage between 110 and 140 °K. The damage causing a decrease in the 0.89 μm luminescence emission band anneals partially (40%) in the same temperature range (110 to 140 °K). The remainder of the damage causing a decrease in the 0.89 μm luminescence emission band anneals in a continuous manner between 140 °K and room temperature.
Study of Electron Lifetime in p‐Si
Authors: Abdullaev G. B. , Iskender‐Zade Z. A. , Dzhafarova E. A. , Chelnokov V. E.
Published: July 2007

The lifetime τn of minority carriers in p‐Si is studied over a wide range of temperatures (17 to 245 °C) and injection levels (0.05 to 6). It is found that at a temperature of T ≈ 160 °C and within the injection level range Δ = 0.05 to 2.5, τb ≈ 35 μs; below this temperature, τn increases from 1 to 20 μm, and above it, decreases from 160 to 55 μs with increasing directly flowing current through the p‐n junction. Comparison of the experimental results with the Shockley‐Read theory indicates that within the range Δ = 0.5 to 6, recombination takes place via donor‐type centres (σn/σp = 1.7) situated (0.36 ± 0.02) eV above the edge of the valence band. These levels are therefore attributed to atoms of gold in the p‐Si.
Bubble Diffusion and the Motion of Point Defects near Surfaces. (Diffusion Theory for Discrete Media, Part IV
Authors: Kelly R.
Published: July 2007

The theory of diffusion of inert‐gas bubbles in solids is important in a variety of fields, including reactor technology, ion bombardment, powder metallurgy, and the study of large defects. Bubble diffusion also provides a convenient frame of reference for discussing the motion near surfaces of point defects, i.e. of surface defects, vacancies, and vapourized atoms or molecules. It is shown that the bubble diffusion coefficient, Db, for a surface‐diffusion mechanism is equal to (3/2 π a4) Ds, where a is the bubble radius in units of λ, the mean atomic spacing, and that this expression is independent of the surface‐diffusion jump distance. The formation of vacancies at a surface should occur at a frequency given by Γfv = Dvol α/f pvλ2 per area λ2 of the surface, where αv is the vacancy condensation efficiency, f is the correlation factor, and pv (in units of λ) is the atom layer spacing next to the surface. With this assumption, Db for a volume‐diffusion mechanism will be equal to (3/2 π a3 f) Dvol. The frequency at which vapourized atoms or molecules are formed is shown to be given by a relation very similar to that for vacancy formation. The corresponding expression for Db, i.e. that for a vapourization‐condensation mechanism, is of the form (3/4 π a3) (Dg Cg λ3), where Dg is the vapour diffusion coefficient and Cg is the equilibrium vapour concentration in atoms/cm3.
Preparation of Cu2Se Single Crystals and Investigation of their Electrical Properties
Authors: Abdullaev G. B. , Aliyarova Z. A. , Asadov G. A.
Published: July 2007

A study is made of the electrical conductivity, σ, the thermo e.m.f., α, and the Hall constant, R, in single crystals of Cu2Se. The temperature dependence of these phenomena in the range 22 to 650 °C is also investigated. From the temperature dependence of σ a value of 1.2 eV is found for the activation energy, ΔE, in the inherent region, whereas the value obtained from the optical absorption edge is 1.3 eV.
Fließspannung und Versetzungsdichte Kalzium‐dotierter NaCl‐Einkristalle
Authors: Hesse J.
Published: July 2007

Kalzium‐dotierte NaCl‐Einkristalle werden im dynamischen Druckversuch verformt. Die Änderung der Verfestigungskurve (VK) und des Zusammenhangs von Versetzungsdichte N und Schubspannung τ mit dem Ca‐Gehalt werden bestimmt. Die VK erweist sich als dotierungsabhängig: Der Verfestigungsanstieg im Bereich I und die Länge dieses Bereichs nehmen mit steigendem Ca‐Gehalt zu. Der Verfestigungsanstieg im Bereich II ist dagegen von der Dotierung unabhängig. Der lineare Zusammenhang von τ und N, der für “reines” NaCl erst im Bereich II gefunden wird, setzt für Ca‐dotiertes NaCl schon im Bereich I ein. Für Ca ⪆ 60 ppm gilt dann τ ∼ N bereits an der kritischen Schubspannung. Diese Ergebnisse werden in Verbindung mit der Temperaturabhängigkeit der Verfestigungsparameter diskutiert.
The Geometry and Energy of a Twist Boundary between Crystals with Unequal Lattice Parameters
Authors: Jesser W. A. , Kuhlmann‐Wilsdorf D.
Published: July 2007

The geometry of “twist‐misfit boundaries” is investigated. These are dislocation networks such as arise in the interfaces between epitaxial overgrowths and substrates with unequal lattice parameters when they are slightly twisted relative to each other with respect to an axis normal to the interface. In the particular cases examined the interface has simple cubic or close‐packed hexagonal symmetry. By introducing the equations obtained for the dislocation spacings and orientations into the theory of interfaces developed by Frank and van der Merwe, the interfacial energy is calculated as a function of misfit and twist. By further combining the expressions thus derived with the theory of Cabrera, the equilibrium elastic strain in hemispherical epitaxial nuclei on infinite substrates is calculated. This is found to decrease with increasing size and with increasing misalignment of the nuclei. Because of the complexity of the equations, all numerical computations were performed with a B 5500 computer.
Kronig‐Penney‐Type Calculations for Electron Tunneling through Thin Dielectric Films
Authors: Schnupp P.
Published: July 2007

Using a Kronig‐Penney model and matrix methods the probability D = exp ( − 2 χ a) of an electron tunneling through a thin dielectric film can be calculated exactly for an arbitrary value of the thickness a. The relation between the damping constant χ and the electron energy E in the band gap of the dielectric depends on the thickness a. For thick films containing more than 10 to 15 crystal planes the E(χ2)‐curves approximate to the usual ones obtained from band theory. However, the simple model involving potential walls without any potential wells is the limiting case for very thin films. Nevertheless, the departure of the complex band structure of the dielectric from the free electron‐approximation usually used in tunneling calculations should be observable qualitatively even for very thin films.
Microprobe Investigations of Copper Precipitates in Silicon Single Crystals
Authors: Fiermans L. , Vennik J.
Published: July 2007

Microprobe investigations of copper precipitates in silicon single crystals, confirm and extend the geometrical analysis performed by means of infra‐red microscopy. Evidence is obtained which proves that the concentration of carbon or oxygen is enhanced at the centres of the precipitates. This is in agreement with the proposed mechanism for the nucleation and growth of the copper precipitates i.e. indentation at SiO2 or SiC centres. Some effects concerning surface contamination are also examined.
Thermal Expansion and Compressibility of Solid Neon and Xenon
Authors: Gupta N. P. , Dayal B.
Published: July 2007

The lattice constants and isothermal compressibility of solidified neon and xenon are calculated at various temperatures for the harmonic approximation. An (exp, 6) potential function is used and zero‐point energy is included in the same way as in earlier papers. The theoretical and observed values of lattice constants and compressibility agree reasonably well for xenon but not so well for neon. It is suggested that the interaction in neon is somewhat analogous to that in helium, and the usual potentials which are applicable to heavy rare gas solids i.e. argon, krypton and xenon, are not suitable for neon.
Über die Messung der Anisotropie der galvanomagnetischen Transversalspannung an Einkristallfolien
Authors: Lück R. , Saeger K. E.
Published: July 2007

Die Grundlagen der Meßmethode werden theoretisch begründet, und die Anwendbarkeit wird abgegrenzt. Über Meßergebnisse eines zusätzlich zum Halleffekt auftretenden Nebeneffektes (transverse‐even voltage) an Kupfereinkristallen wird berichtet. Die Messungen wurden bei 4,2 °K in Abhängigkeit von Orientierung und magnetischer Feldstärke durchgeführt. Mit Hilfe einer neuen allgemeingültigen Beziehung zwischen diesem Effekt und dem Widerstand im Magnetfeld, die auch den sättigenden Anteil des Widerstandes berücksichtigt, wird der Winkel zwischen Stromrichtung und Richtung der offenen Bahnen berechnet und die Übereinstimmung mit röntgenographisch gewonnenen Werten überprüft. Die Feldabhängigkeit dieses Effektes wird benutzt, den Widerstand im Magnetfeld in einen sättigenden und einen mit der magnetischen Feldstärke quadratisch ansteigenden Anteil zu zerlegen.
Infrared Fluorescence in Manganese Activated Zinc Sulphide Phosphors
Authors: Agrawal J. P.
Published: July 2007

A luminescence emission in the 3.00 μm region is reported for manganese activated zinc sulphide phosphors where the manganese concentration is greater than 2%. Optical absorption measurements show a maximum at 0.80 μm with sub‐bands at 0.74 and 0.84 μm, the luminescence being excited by radiation in this region. It is suggested that a new luminescence centre is formed as a result of Mn2+ ions perturbing the host‐lattice.
Oszillationen der Oberflächenimpedanz von Wolfram in schwachen Magnetfeldern
Authors: Herrmann R.
Published: July 2007

In Magnetfeldern von 1 bis 150 Oe werden Oszillationen der Oberflächenimpedanz von Wolfram bei einer Frequenz des elektromagnetischen Feldes von 9,38 GHz in den kristallographischen Ebenen (10) und (001) bei einer Temperatur von 1,6 °K beobachtet.
A Comparison of Electron Microscope Images of Dislocations Based on Isotropic and Anisotropic Elasticity Theory
Authors: Humble P.
Published: July 2007

A comparison is made between the electron diffraction images of dislocations computed on the basis of isotropic and anisotropic elasticity. It has been shown previously that for highly anisotropic materials, such as β‐brass, considerable contrast is obtained in the case of screw dislocations for which g · b = 0 and in the case of edge dislocations for which g · b = 0 and g · b × u = 0. The present calculations indicate that under these conditions some contrast would also be expected for dislocations in materials such as iron, niobium, copper and gold, which are considerably less anisotropic then β‐brass, providing the dislocations do not lie normal to an elastic symmetry plane. However, in most cases for which g · b ≠ 0, the approximation of isotropic elasticity is an adequate basis on which to deduce the character of the electron diffraction images of dislocations, even in highly anisotropic materials.
The Influence of the Size Effect on Electrical Resistivity Measurements in Irradiated Metals
Authors: Dworschak F. , Schuster H. , Wollenberger H. , Wurm J.
Published: July 2007

Two high purity Al foils of thickness 40 μm and 5.6 μm are simultaneously irradiated. The initial resistivity increments per unit defect concentration for the foils differ by a factor of two due to the size effect. Sondheimer's theory is in good agreement with the experimental data. The calculations are presented for a range of parameters so that the magnitude of this effect can be estimated for other experiments.
Peculiarities of the Magnetoresistance in Bi in High Transverse and Longitudinal Magnetic Fields
Authors: Bogod Yu. A. , Eremenko V. V.
Published: July 2007

Results are presented of experimental studies of magnetoresistance of oriented Bi single crystals in pulsed transverse and longitudinal magnetic fields up to 90 and 160 kOe, respectively, at 4.2, 20.4, and 77 °K. The changes of the magnetic field dependence of the resistance observed previously [5] i.e. the tendency towards saturation, are studied in detail. Magnetoresistance anomalies are shown to appear in transverse and longitudinal magnetic fields at similar field strengths. An attempt is made to relate the results to the occurrence of open paths in high magnetic fields.
On the Low‐Temperature Internal Friction in Silicon
Authors: Kromer P. F. , Khiznichenko L. P.
Published: July 2007

The internal‐friction relaxation peak observed in silicon single crystals [6, 7] is discussed using Brailsford's concept of “built‐in” kinks on dislocations. The numerical estimates of the theory agree satisfactorily with the experimental data. The correlation of two theories based on thermally generated and “built‐in” kinks is also considered.
Mössbauer Effect in FeF3
Authors: Bertelsen U. , Knudsen J. M. , Krogh H.
Published: July 2007

The antiferromagnetic compount FeF3 is studied by the Mössbauer technique in the temperature range from 300 to 400 °K. A Néel temperature TN of (362.4 ± 0.2) °K is deduced from the data. If the reduced hyperfine field is represented by h(T) = D (1 − T/TN)β, it is found that β = 0.358 ± 0.013 in the region 0.81 < T/TN < 0.99. The shapes of the peaks in the Mössbauer spectra in the vicinity of the Néel temperature are discussed.
F‐Centers in SrF2
Authors: den Hartog H. W. , Arends J.
Published: July 2007

Results are presented of ESR experiments and optical measurements on F‐centers in additively colored SrF2 crystals. The hyperfine interactions between the unpaired electron and the surrounding nuclei are discussed and compared with the results obtained for F‐centers in CaF2 and BaF2. Combined results of ESR experiments, optical measurements, and bleaching experiments indicate that the absorption band at 4490 Å arises from an electron trapped in an F− vacancy. It appears that there is no correlation between the absorption bands at 4490 and 6350 Å.