bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Band Structures of Four Polytypes of Silicon Carbide Calculated with the Empirical Pseudopotential Method
Authors: Junginger H.‐g. , van Haeringen W.
Published: July 2007

The electronic band structures of four polytypes of silicon carbide (3C, 2H, 4H, 6H) are calculated with the aid of local atomic pseudopotentials for carbon and silicon. The same pseudopotentials are used in all four polytypes. A description is given of the basic assumptions in the empirical pseudopotential method. A computer program is used which is able for symmetric k‐values to reduce the dimensionality of matrices. The calculated energy band structures are in satisfactory agreement with well‐established experimental data.
X‐Ray Interferometric Measurements of the Forward Scattering Amplitude for Lithium Fluoride
Authors: Creagh D. C. , Hart M.
Published: July 2007

The X‐ray refractive index of lithium fluoride was measured to an accuracy of a few parts in 109 over the wavelength range from AgKβ1 (λ = 0.497058 Å) to CuKα1 (λ = 1.54053 Å). From these results the scattering factor for the forward direction and the anomalous dispersion corrections for fluorine were calculated. Good agreement was obtained with the values calculated using Hönl's dispersion theory.
Acoustical Scattering in Polar Semiconductors at Strong Electric Fields
Authors: Licea I.
Published: July 2007

The processes of acoustical scattering by a strong electric field in semiconductors with an arbitrary non‐parabolicity of the spherically symmetric conduction bands are considered in the electron temperature approximation. Assuming only acoustical scattering the energy and momentum conservation equations are established when both energy and momentum exchange is controlled by interelectronic collisions. Basing upon these results, the electron temperature and mobility in a polar semiconductor with a non‐parabolic energy dispersion law as that of n‐type InSb are studied theoretically. The problem is treated for “warm” and “hot” electrons and a comparison is made with the parabolic case.
Study of the (111) Conduction Band of GaSb
Authors: Averous M. , Bougnot G. , Calas J. , Chevrier J.
Published: July 2007

We have developed a calculation method of the parameters of the (111) band of GaSb from measurements of piezoresistance under uniaxial stress and hydrostatic pressure, and from the Hall effect as a function of temperature. We have determined dδE/dp, m, m, K (ellipsoid anisotropy), and Ξu, the deformation potential constant for the (111) band.
Concentration Correlations, Velocity Correlations, and Transport Noise in Quasineutral Semiconductors
Authors: Sergiescu V.
Published: July 2007

The non‐local decomposition of the transport noise formerly introduced by the author is performed for a quasineutral semiconductor. The Hill‐van Vliet formula for the current noise is rederived, the Nyquist formula for the thermal noise is found to be approximately valid in the stationary regime, and the coupling noise is found to be negligible because of the statistical reversibility. The noise effects of the Coulomb and delta correlations are comparable, but opposite, in the most interesting cases.
Electron Energy Loss and F‐Centre Production in KCl and KBr
Authors: Choudhury A. , Goswami K. , Chaudhuri S.
Published: July 2007

A rotating cylindrical crystal of KCl was bombarded by 19 keV electrons, and the F‐centre distribution observed as a function of the angle of rotation. Eight maxima were found corresponding to different angular positions of the crystal. The depth of coloration was measured along the <100> and <110> axes in KCl and KBr crystals. In both the crystals the magnitude of coloration was higher along <110> axes than along <100> axes, but the depth of coloration or the electron range had been found to be longer along the latter direction. The results are interpreted in terms of channeling effect.
On the Faraday and Voigt Effects in Anisotropic Materials
Authors: Saleh N. , Zukotynski S.
Published: July 2007

The Faraday rotation and ellipticity and the Voigt effect in degenerate semiconductors possessing ellipsoidal energy surfaces are analyzed. It is shown that if the experimental procedure is chosen properly, information on the effective mass and relaxation time tensors can be readily obtained.
Inductions and Echoes in Systems with Unequidistant Spectrum
Authors: Nagibarov V. R. , Solovarov N. K.
Published: July 2007

A general method is developed of calculation of response signals of N‐particle systems with an unequidistant spectrum to pulse action of coherent physical fields resonant for any transition of the system. The case of a particle system where each particle has three energy levels E1 < E2 < E3 is analysed. It is shown that if such a system is subjected to pulse action of two generators exciting transitions E1 ⟷ E2 and E2 ⟷ E3 at initial time and at time τ to pulse action of a generator with frequency ω31 = h−1 (E3 — E1), the system generates induction and echo signals with power proportional to N2 at all possible transitions. Echo signals arise at times (1 + ϵ) τ, 2 τ, and (1 + 1/ϵ) τ after the first pulse, where ϵ = E2 — E1/E3 — E2. The observed responses may have a physical nature which is both identical with the excitation and different from it. Supplements are given by which the responses of particle systems may be calculated to a series of pulses different from those considered here. When ϵ →1 the results transform to the case of equidistant spectrum.
Scattering of Fast Charged Particles on Crystals
Authors: Ryabov V. A.
Published: July 2007

The angular distribution of fast charged particles scattered on a perfect crystal is studied. By introducing the many‐particle correlation functions the velocity distribution function convenient for numerical analysis is obtained. It is shown that this distribution depends essentially on correlations between the thermal atomic displacements of a lattice. A two‐particle model is considered as a particular case, which results are compared with experimental data. It is evident that even in this simplest case the axial symmetry of the scattering yield is disturbed. This is determined by the difference of the various correlation tensor's components as found.
The Defect Structure of Non‐Stoichiometric Germanium Telluride from Magnetic Susceptibility Measurements
Authors: Lewis J. E.
Published: July 2007

The room temperature magnetic susceptibility of non‐stoichiometric GeTe has been measured; by calculating the contributions of the free carriers and the ionic lattice using the appropriate formulae and the known parameters of the system, the contribution to the susceptibility of the lattice defects has been obtained as a function of composition. Analysis of this lattice defect susceptibility shows that vacancy and anti‐structure defects are predominant in the non‐stoichiometric lattice and that their density is extremely high.
A Simple Straight‐Forward Method to Calculate the Correlation Factor and Its Relation to the Isotope Effect for Impurity Diffusion
Authors: Bakker H.
Published: July 2007

A general formalism is developed by which it is possible to relate the correlation factor to the isotope effect and to calculate the correlation factor for impurity diffusion by monovacancies in systems having at least a twofold symmetry around the vacancy–solute jump direction. However, the formalism can be extended to more complicated systems. Some well known results are deduced easily from a general equation. The case of impurity diffusion in the two‐dimensional hexagonal lattice and in the three‐dimensional f.c.c. lattice is worked out completely.
Many‐Beam Diffraction Effects in Gold and Measurement of Absorption Parameters by Fitting Computer‐Graphs
Authors: Steeds J. W.
Published: July 2007

A computer simulation of electron micrographs has been described previously (Spring and Steeds [1]). The method is here applied to the case of gold where many‐beam effects become important. Measurement of the absorption parameters are made at 600 and 100 keV for the hhh systematics and compared with predicted values. The comparison of computer simulated and experimental bend contours shows agreement only when the atomic scattering potential is also carefully chosen. A simple classification of bend contours is made using both cross‐hatching effects and also central channelling and realised theoretically through analytic four‐beam theory. The change of channelling properties with accelerating voltage is discussed.
EPR of Fe3+ Ions in Chrysoberyl
Authors: Barry W. R. , Troup G. J.
Published: July 2007

A redetermination of the spin Hamiltonian parameters for Fe3+ ions substituting for Al3+ ions in mirror symmetry sites in the orthorhombic mineral chrysoberyl (Al2BeO4) has been made. EPR experiments at X‐ and Q‐band frequencies are described, and analysis of the measurements yields new values for the parameters, given by g = 2.003 ± 0.001, b = (8.572 ± 0.006) GHz, b = (–0.311 ± 0.003) GHz, b = = (0.014 ± 0.015) GHz, b = (1.461 ± 0.006) GHz. The zero‐field splittings between the ± 5/2 and ± 3/2, and the ± 3/2 and ± 1/2 Kramers' doublets are (32.78 ± 0.03) GHz and (19.6 ± 0.2) GHz, respectively.
Diffusion and Thermal Conversion of Crowdions
Authors: Seeger A.
Published: July 2007

Thompson and Buck have demonstrated by internal friction measurements that self‐interstitials in copper may exist in two configurations, a stable and a metastable one. The metastable configuration may be converted by thermal fluctuations into the stable configuration. The present paper develops a simple model for dislocation pinning by crowdions, taking into account thermal conversion. The results clearly indicate that the metastable interstitial in Cu migrates in one dimension, i.e., that it is a crowdion. The temperature dependence of the pinning rate is accounted for by a conversion energy barrier that is in agreement with other data.
Three‐Dimensional versus Crowdion Migration of Interstitials in Annealing Stage I of Irradiated Metals
Authors: Schilling W. , Schroeder K. , Wollenberger H.
Published: July 2007

Formulas for the defect production rates are derived for the case that interstitials are highly mobile at the irradiation temperature thereby either recombining with vacancies or being trapped at impurities. Both the migration of interstitials in three dimensions and the linear migration of crowdions are considered. For the crowdion model the possibility of thermal conversion is included. Experimental observations of the defect production rates in f.c.c. metals at temperatures above stage I confirm qualitatively and quantitatively all the predictions of the model which assumes three‐dimensional interstitial migration. The predictions of the crowdion model are by orders of magnitude in disagreement with the experimental results. Especially the very specific dependence of the defect production rates on the impurity concentration and irradiation temperature predicted by the crowdion model is not observed. In the Appendix the interpretation of the dislocation pinning experiments in terms of the crowdion model is criticized.
New Evidence for F′‐Type and Ionized F‐Aggregate Centres
Authors: Nosenzo L. , Reguzzoni E. , Samoggia G.
Published: July 2007

If the ionization probability of an optically excited defect is varied periodically by means of an external electric field of frequency v, a corresponding modulation in the absorption coefficient in the bands associated either with the neutral centre or with the ionized and F'‐type centres can be achieved. In fact the results obtained on M‐ and R‐centres in KCl and KBr crystals at liquid nitrogen temperature give new evidence of the existence of absorption bands associated with M+‐, R+‐, M'‐, and R'‐centres. A new set of absorption bands has been observed associated with ionized R‐centres and ascribed to electronic transitions to different excited states. These bands are located at 0.94, 0.76, 0.54, and 0.49 μm in KCl and at 1.01 and 0.89 μm in KBr. Besides the bands due to ionized N1‐centres, an absorption band has been observed in the infrared, which has been tentatively attributed to N1‐centres.
The Electrical Properties of Chromium Tribromide
Authors: Kanazawa K. K. , Street G. B.
Published: July 2007

The electrical properties of vapor grown crystals of the hexagonal layer lattice material CrBr3 have been measured. From the temperature dependence of the Seebeck voltage and the resistivity it is concluded that the transport of the majority carriers, electrons, occurs by a hopping process. The activation energy for electron mobility is 0.56 eV for conduction along the c‐axis and 0.39 eV for conduction in the (0001) plane. The values of the effective drift mobilities in these two directions are 10−10 cm2/Vs and 10−7 cm2/Vs, respectively. Comparison of optical and photoconductivity data indicated that photoconductivity is associated with the crystal field optical transitions as well as the charge transfer bands.
Resistivity Change of Point Defects during Work Hardening of High‐Purity Copper
Authors: Thom F.
Published: July 2007

The electrical resistivity of high‐purity copper deformed by torsion is examined after deformation and after annealing out of the point defects. Deformation is carried out at 4.2, 20.4, and 90.2 °K, and the increase of resistivity is recorded at 20.4 and 90.2 °K for a number of samples. Measuring temperatures near 80 °K prove to be unreliable for the observation of lattice defects. In accordance with Saada's theory the point defect concentration is found to rise proportional to \documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{*{20}c} {\gamma _2 } \\ \int \\ {\gamma _1 } \\ \end{array}\tau (\gamma) $\end{document} at temperatures ≦ 20.4 °K if the measurements, too, are made at such temperatures. If, however, similar measurements are made after deformation at 90.2 °K the data obtained differ markedly from the Saada relation.
On Mechanism of Electron Scattering in InP
Authors: Galavanov V. V. , Siukaev N. V.
Published: July 2007

The Hall mobility of electrons was studied in n‐InP single crystals in the temperature range from 77 to 1000°K at electron concentrations n = 2 × 1015 to 2 × 1017 cm−3 and mobilities μ = 3 × 103 to 4.3 × 104 cm2/Vs. The results agree well with calculations for the mixed mechanism of electron scattering on optical phonons, μ0 = (100/√T)(exp(500/T) −1), and acoustic phonons, μa = 6.53 × 107 T−3/2 cm2/Vs (the deformation potential is assumed to be equal to 21 eV). Scattering on ions and neutral impurity atoms is important in specimens with n > 5 × 1015 cm−3 at low temperatures. The concentration of neutral impurity atoms does not exceed 1014 cm−3 in pure specimens, while in specimens with n > 1016 cm−3 NN reaches the value of 1016 cm−3 and more. The results of the Hall coefficient dependence on the magnetic field strength (0.3 to 20 kOe) at 77 and 300 °K show that the Hall factor A (R = A/nec) approximates 1 in all the specimens with the exception of pure specimens where A ≈ 1.13 at 77 °K. These results agree well with the conclusions drawn from the analysis of temperature and concentration dependences of mobility.
Anomalous Transmission of X‐Rays for Divergent Incident Beam
Authors: Kovev E. K. , Korovin L. I. , Efimov O. N.
Published: July 2007

It is shown that the analytical form of some characteristics of the anomalous transmission of X‐rays for divergent incident beam is different from the corresponding expression derived for the case of parallel beam. In particular, the expressions for the reflection coefficient and half‐width are modified, while the integrated intensity preserves the same meaning. The new content of the reflection coefficient makes it possible to use it for obtaining the integral characteristics of anomalous transmission, connected with different parts of the structure factor. Consideration of the divergence of the incident beam leads to a good agreement of the experimental and theoretical data for the characteristics of anomalous transmission.
Adsorption and Nucleation of Silver on Tungsten
Authors: Sugata E. , Takeda K.
Published: July 2007

Adsorption of silver on tungsten has been studied by field emission microscopy in the temperature range from 78 to 1000 °K varying the impinging flux 0,2 to 1.0 monolayer per min. Silver atoms are found to deposit without detectable surface migration at 78 °K substrate temperature on planes other than {110}. Activation energy for surface migration over {100}‐planes is 0.8 eV. The average work function slightly increases from the original value of 4.5 eV at depositions of a small amount of silver and decreases then to 4.0 to 4.2 eV with deposit thickness. The activation energy for desorption in the coverage interval θ = 0.4 to 0.1 and θ = 0.7 to 0.5 are found to be 2.8 and 2.0 eV, respectively. Critical adatom coverage for nucleation is also measured as a function of substrate temperature and impinging flux.
Isotope Inter‐Diffusion and Self‐Diffusion in Solid Lithium Metal
Authors: Lodding A. , Mundy J. N. , Ott A.
Published: July 2007

The inter‐diffusion of Li isotopes in separated 7Li and 6Li metals has been measured in the temperature range 35 to 178° C. The results can be expressed as
equation image
where 7D6 denotes the diffusion of 6Li tracer in pure 7Li metal, and vice versa. The 7D6‐values exceed 6D7 by about 23% at the melting point and by about 37% at 0.7 Tm (°K). There are indications that the striking isotope effect may be due to tunneling. Tunneling considerations founded on a square barrier approximation suggest a dumbbell interstitial mechanism as a likely self‐diffusion model for lithium. According to the calculation for the dumbbell, the contribution from the tunneling process to the effective energy of self‐diffusion is of the same order as, or smaller than, than, the potential barrier to activated motion. Without favoring any particular diffusion model, the following expressions can be computed for uncorrelated self‐diffusion in isotopically pure lithium metals:
equation image
(diffusion coefficients in cm2/S, energies in kcal/mol).
The γ‐Ray‐Induced Electric Conductivity of Fused Silica as Dependent on Field Strength, Temperature, and Irradiation Time
Authors: Onnasch D.
Published: July 2007

The γ‐ray‐induced electric conductivity in fused silica is studied theoretically and experimentally as a function of temperature, electric field strength, sample thickness, and irradiation time. Synthetic glasses containing water show the highest induced conductivity. Caused by an increase of positive centres capturing the excited electrons, the conductivity decreases as t−α with the irradiation time t, where α < 1 is a constant depending on temperature. Within the range from 8 to 300 °K, induced currents are measured with voltages up to 2500 V and dose rates between 10 and 200 mrad/s in synthetic samples, 0.2 to 4 mm thick. The gradual transition from constant conductivity at high temperatures and low field strengths F to an increase of conductivity proportional to F cr F3/2 at low temperatures and high field strengths is explained by the deformation of the Coulomb potential of 2 × 1012 to 5 × 1014 cm−3 singly ionized, electron‐capturing centres under the action of the applied field. The comparison of the theoretical dependence of the electron lifetime on field strength and temperature with the measurements allows to conclude that the mobility is independent of temperature. This implies the elastic scattering of the electrons at about 3 × 1019 cm−3 neutral impurities. Furthermore, the mean free path of the electrons for loss of a phonon at 8 °K is determined to be 106 Å.
Current Saturation in Irradiated Synthetic Fused Silica
Authors: Onnasch D.
Published: July 2007

The γ‐ray‐induced current in synthetic fused silica (containing water) is saturated at field strengths ⪆ 1.4 × 104 V/cm caused by two effects. Besides the schubweg saturation known from photoconductors with blocking contacts, the saturation of the drift velocity of the electrons at the level of the velocity of sound is demonstrated. In some samples, especially at lower temperatures, the effect is accompanied by instabilities of the induced current explained by charge redistributions.
Étude de la molécule trichromique d'acétate complexe Cr3(CH3COO)6OCl · 5 H2O
Authors: Munschy G.
Published: July 2007

A partir des fonctions d'onde du quadruplet de spin fondamental de l'ion chromique, on construit des fonctions pour la molécule à trois ions paramagnétiques en interaction d'échange. Pour l'essentiel, le spectre des niveaux d'énergie, donné par un hamiltonien de spin I0 (s1 s2 + s2 s3 + s3 s1) de trois spins 3/2 en interaction, dépend d'un nombre quantique de spin, S. Le fait nouveau réside dans l'intervention des variables orbitales pour le calcul de la structure fine des niveaux S. Pour la première fois, on obtient ainsi un accord satisfaisant avec la courbe expérimentale de la chaleur spécifique aux températures de l'hélium liquide.
Fermi Surface of Tellurium
Authors: Guthmann C. , Thuillier J. M.
Published: July 2007

A study of the Shubnikov‐de Haas effect allowed us to determine the Fermi surface of tellurium. At low impurity concentration, the Fermi surfaces are ellipsoidal. When the impurity concentration increases, the ellipsoids coalesce and form a dumb‐bell surface. For p ≈ 1.5 × 1017 cm−3, the ellipsoids are just joining together. From the experimental results obtained in this concentration range, we have been able to calculate some parameters of the valence band, which are in good agreement with the theoretical model.
Anregungswahrscheinlichkeit von Oberflächenplasmonen bei schrägem Elektroneneinfall unter Berücksichtigung der Retardierung
Authors: Dobberstein P.
Published: July 2007

Die differentielle Anregungswahrscheinlichkeit für Oberflächenwellen bei Anregung durch schräg auf eine Metalloberfläche treffende schnelle Elektronen wird im Rahmen der dielektrischen Theorie unter Berücksichtigung der Retardierung berechnet. Numerische Werte für Silber werden diskutiert.
Diagram Expansion at Finite Temperatures in the Real Time and Frequency Domains
Authors: Sandström R.
Published: July 2007

A method is given for obtaining diagram expansions at finite temperatures in domains for real times and frequencies. As an example the diagram expansions for electrons (in the ordinary electron gas approximation) and phonons are discussed. Network rules are established to obtain all kinds of self energies and propagators in a systematic and simple way. These specify the way in which the different types of propagators G, G≷, Gr. a for, e.g., electrons should be linked together. Generalized Dyson equations for the different electron and phonon propagators are given. As the results are significant both for non‐equilibrium and equilibrium phenomena the corresponding diagram expansions are discussed in terms of the space in which they are most easily handled namely ordinary space and Fourier space, respectively. A diagram dictionary including the network rules is also presented. Finally, the evaluation of screened diagrams is given as an example.
Stray‐Field‐Free and Related Domain Wall Configurations in Thin Magnetic Films (II)
Authors: Hubert A.
Published: July 2007

In Part I [2] it was shown that Bloch walls in thin magnetic films should have a vortex‐like asymmetric and largely stray‐field‐free structure. A rigorous proof of the existence of an analogous asymmetric model for the Néel wall has not yet been given. Therefore, the earlier calculations have been extended in two directions: (i) Bloch walls are calculated also for applied fields. These walls lose the remaining (y) symmetry found in the 180° Bloch walls. The calculations show that their energy increases with increasing applied field. (ii) Néel walls are constructed for the entire interesting range of film thicknesses and applied field values, thus forming a continuous transition from the symmetrical Néel wall at small thicknesses and high fields to the walls with an asymmetric core at large thicknesses and small fields. In fields larger than 0.3 (2 K/Is) only Néel walls are stable for all thicknesses; they may be symmetrical or asymmetric, depending on film thickness and the magnitude of the field. For all walls wall widths are calculated for the purpose of comparison with electron microscope observations.
Notes on the Influence of Spin on the Electrical Conductivity in Strong Magnetic Fields
Authors: Keiter H. , Hajdu J.
Published: July 2007

The longitudinal and transverse electrical conductivity for a system of free electrons interacting with short‐range impurities is calculated. Since in the lowest order Born approximation the transverse conductivity diverges, and the longitudinal conductivity shows unphysical zeroes for certain values of the magnetic field, higher order t‐matrix treatment is required. We obtain spin splitting of the Shubnikov‐de Haas oscillations for spin independent and spin dependent scattering. Compared with the transverse case, the first (0+) maximum is absent in the longitudinal case, provided that no spin flip occurs. Spin flip in the scattering process, however, gives rise to a 0+ maximum. Apart from this fact, the spin flip causes no remarkable change in the oscillatory behaviour of the conductivity.
The Establishment of Long‐Range Order in Ni2Cr Using Electron Microscopy
Authors: Klein H. J. , Brooks C. R. , Stansbury E. E.
Published: July 2007

Using selected area diffraction in transmission electron microscopy, long‐range order in Ni2Cr has been clearly detected. Specimens showing order had been aged for 630 h at 500 °C or for four months at 479 °C. The domain size for the specimen aged at 500 °C was about 100 Å, but the domains for the specimen aged at 479 °C were too small to be resolved.
Spatial Dispersion Effects in the Optics of Metals
Authors: Silin V. P. , Fetisov E. P.
Published: July 2007

The oblique incidence of a light wave on a plane boundary is considered using the method of kinetic equation. The main attention is payed to the study of the influence of longitudinal plasma wave excitation in metals on surface energy losses of light waves and on volume losses in the case of P‐polarization. The significance of Fermi‐liquid effects is considered in detail. An asymptotic behaviour of the field inside the metal is observed for long distances from the boundary.
Prismatic Slip in Beryllium and the Relative Ease of Glide in H.C.P. Metals
Authors: Regnier P. , Dupouy J. M.
Published: July 2007

The macroscopic C.R.S.S. for prismatic slip in Beryllium is found to increase with increasing temperature in the range −100 to +50 °C while the microyield limit decreases regularly. Slip is initiated on the prism planes from the edge dislocations present in the annealed material. Evidences of a thermally activated locking of screw dislocations are presented. This locking is thought to occur by the usual splitting in the basal plane. The assumption that the a dislocations can also dissociate in the prismatic plane seems necessary to account for the activation of this locking. Possible dissociations in the prismatic plane are proposed; the most probable of them is a → a/3 + 2 a/3. It gives a ribbon of stacking fault corresponding to the transformation of two {1010} h.c.p. “flat planes” into two {112} b.c.c. planes. It is suggested that there is a relationship between the energy of the stacking fault on the prismatic plane and the temperature of the phase transformation h.c.p. → b.c.c. This relationship permits to account for the relative ease of slip in h.c.p. metals.
Magnetic Properties of the Hexagonal Iron Nitride ϵ‐Fe3.2N
Authors: Eickel K. H. , Pitsch W.
Published: July 2007

The Mössbauer effect has been measured on powder samples of the h.c.p. iron nitride ϵ‐Fe3.2N at 295 °K. The measurements indicate, that there are two kinds of Fe‐atoms with different environments in this material. This is in accordance with previous X‐ray investigations by which it was found that in ϵ‐iron nitrides the N‐atoms are highly ordered in such a way that e.g. in ϵ‐Fe3.2N the Fe‐atoms have either one or two N‐atoms within their nearest neighbourhood. Furthermore the average magnetic moment of the Fe‐atoms in ϵ‐Fe3.2N has been measured to be 1.97 μB. Using this value together with the Mössbauer data the magnetic moments of the Fe‐atoms are estimated. The moments obtained are 2.4 μB and 1.9 μB respectively. These values are interpreted by similar considerations by which the magnetic structure of the f.c.c. γ′‐iron nitride Fe4N has been explained previously in the literature.
Infrared Piezoabsorption of Silicon in the Multiphonon Spectral Range
Authors: Lüth H.
Published: July 2007

Piezoabsorption measurements have been performed on silicon in the multiphonon spectral range (500 to 1000 cm−1). Uniaxial stress along [100] is applied and the light is polarized parallel and normal to the stress axis (‖ and ⟂ [100]). The change of the absorption constant induced by hydrostatic pressure is calculated from the results. Sign and location of the piezoabsorption bands yield a topological classification for the critical points which give rise to the two‐phonon absorption structure in silicon.
Dislocations in Extruded β′‐NiAl
Authors: Lloyd C. H. , Loretto M. H.
Published: July 2007

Polycrystalline NiAl which had been plastically deformed at a high temperature has been examined using transmission electron microscopy. It is shown that, in addition to the dislocations of b = 〈100〉, which have been identified by other workers, dislocations of b = 〈110〉 and 〈111〉 contribute to the high temperature plasticity.
Electron Microscopic Study of the Substructure of VO2 due to the Monoclinic to Tetragonal Phase Transformation
Authors: Hayashi Y. , van Landuyt J. , Amelinckx S.
Published: July 2007

Vanadium dioxide has a monoclinic‐tetragonal phase transformation at about 70 °C. This transformation can be induced in an electron microscope during observation, and the boundaries between the monoclinic and tetragonal phases are observed by the diffraction contrast at the interfaces. When the tetragonal phase is transformed into the monoclinic one, the crystal is broken up into domains according to the different modes of transformation. The interfaces between the domains are revealed as fringe patterns in the electron micrographs. The tetragonal‐monoclinic transformation boundaries and the different types of domain boundaries in the monoclinic phase are studied by electron microscopy.
Optical Investigation of the Small Polaron in β‐FeSi2
Authors: Birkholz U. , Naegele J.
Published: July 2007

The reflectivity of α‐FeSi2 and also of β‐FeSi2 doped with Co (n‐type) or Al (p‐type) has been investigated for wavelengths between 1 and 25 μm. The results for α‐FeSi2 indicate metallic conduction in this material. The reflectivity of the undoped semiconducting phase β‐FeSi2 can be explained by a fundamental absorption corresponding to a band gap Eg = 0.8 eV and a reststrahlen band. The highest branch of the longitudinal optical phonons is found at 20.6 μm. The reflectivity of p‐FeSi2 can be interpreted using Drude's theory of free carrier absorption. The optical properties of n‐FeSi2 cannot be explained by free carrier absorption. A consistent interpretation, however, is possible in terms of the small polaron picture. Using the experimental data of the de conductivity and its activation energy the reflectivity of n‐FeSi2 can be calculated. There is good agreement with the observed values. These results confirm an analysis of the transport properties of β‐FeSi2 which was presented in a previous paper.
On the Force Exerted upon Continuously Distributed Dislocations in a Cosserat Continuum
Authors: Minagawa S.
Published: July 2007

The force acting on distributed dislocations in a Cosserat continuum is studied and the expressions for the force and force density are given in tensorial form. The increase in the potential energy of the material body, caused by a displacement of distributed dislocations in a certain region of the body, is obtained. The force acting on those dislocations is deduced by differentiating it with respect to the distance through which the dislocations are displaced. The expression for the density of forces is given as follows:
equation image

where sjni is the tensor of dislocation density, ∑ij the symmetric part of stresses, Mjni the couple‐stress tensor, and ηij the incompatibility tensor.
Acoustoelectric Effect in a Strong Ultrasonic Field
Authors: Paranjape V. V. , Joshi S. B.
Published: July 2007

Average energy of electrons in semiconductors may change under the influence of a strong ultrasonic sound wave. If the change is considered as a sum of energies due to the random part and the drifting part of the electron gas, then it is shown that the former part of the energy may decrease (electron cooling) in certain circumstances. The total change in the energy is, however, always positive, but is shown to be negligible for polar materials.
Thermodynamic Functions of Piezoelectric Polarons in Steady Magnetic Field and Cyclotron Resonance
Authors: Klyukanov A. A. , Pokatilov E. P.
Published: July 2007

The sum over piezoelectric polaron states is calculated at weak and strong magnetic fields. Feynman's path integral variational method is used to calculate the thermodynamic functions, i.e. energy, magnetic susceptibility, and specific heat. Cyclotron resonance of piezoelectric polarons is considered and a comparison of theoretical and experimental results is given.
Anisotropy of Electron and Hole Mobilities in Orthorhombic Sulphur Crystals
Authors: Nitzki V. , Stössel W.
Published: July 2007

The anisotropy of the electron and hole mobility in orthorhombic sulphur has been investigated measuring the transit times of optically generated carriers. The sulphur crystals have been grown from a temperature controlled CS2 solution. The hole mobilities at room temperature along the main directions μp[100] = (7.4 ± 0.4) cm2 V−1 s−1, μp[001] = (4.6 ± 0.3) cm2 V−1 s−1, and μp[010] = (2.3 ± 0.2) cm2 V−1 s−1 decrease with increasing temperature like μp[100], [001] ∼ T−3/2 and μp[010] ∼ T−1. Below room temperature the hole mobilities are trap controlled. The electron transport is an activated process governed by the activation energies ϵn[001] = (0.166 ± 0.003) eV, ϵn[100] = (0.157 ± 0.003) eV, and ϵn[010] = (0.153 ± 0.003) eV. The electron mobilities are interpreted in terms of the small polaron theory.
Investigations of Plastically Deformed Copper Single Crystals in the Stress‐Applied State. I. A Study of the Dislocation Behaviour in the Surface Region and in the Bulk
Authors: Mughrabi H.
Published: July 2007

Copper single crystals oriented for single glide were deformed in tension at 78 °K to various resolved shear stresses and were then neutron‐irradiated at 4 to 20 °K before stress‐removal in order to pin the dislocations in the stress‐applied state. A comparison of transmission electron micrographs obtained from the centre and the surface regions shows that, from early stage II onwards, the dislocation arrangement in the surface region corresponds to a lower stress than that in the centre. At the same time the dislocation density is distinctly lower in the surface region than in the interior. Furthermore, X‐ray investigations show that during deformation the primary glide plane is bent characteristically near the surface in the direction of the slip vector. Details of these results, which are in good qualitative agreement with flow stress measurements and electron microscope work of Fourie, are discussed and compared with the literature.
Zum Einfluß von Versetzungen auf elektrische Eigenschaften von Natriumchlorid
Authors: Froschauer L. , Ilschner B.
Published: July 2007

Die zeitabhängige und die zeitunabhängige elektrische Gleichstromleitfähigkeit von NaCl wurde in Abhängigkeit von der Versetzungsdichte und ‐anordnung gemessen. Es wurde Proportionalität zwischen stationärer Leitfähigkeit und Versetzungsdichte gefunden und auf erhöhte Anionenleitfähigkeit in Versetzungsnähe zurückgeführt. Bei Anlegen der Spannung wurden zwei exponentielle Polarisationseffekte gemessen, von denen der langsamere als Oberflächeneffekt, der schnellere als Volumeneffekt gedeutet wird. Verschiedene Mechanismen zur Begründung werden diskutiert.
Absorption of Ultrasound in Intrinsic Ge, GaSb, and InSb
Authors: Groubert E. , Joullie A. M.
Published: July 2007

An investigation is made of the change of the attenuation coefficient of ultrasonic longitudinal waves with frequencies of 10 to 300 MHz, propagating in monocrystalline Ge. GaSb, and InSb at temperatures of 300 and 77 °K. The measurements were made using the pulse‐echo technique. The results have been treated by the Sylwestrowicz method and fitted with the theories of absorption of sound by Woodruff‐Ehrenreich and Mason‐Bateman.
Theory of Electron Scattering from an Antiferromagnet. I. Heisenberg Model
Authors: De Wames R. E.
Published: July 2007

A calculation of the differential scattering cross sections for scattering of low energy electrons from a Heisenberg antiferromagnet is presented. It is shown that the inelastic and elastic cross sections are proportional to the first and second powers, respectively, of the sublattice magnetization. The derived expressions for the scattering cross sections agree well with recently reported experiments on NiO.
Magnetische Bereiche in Chromtrihalogeniden
Authors: Bostanjoglo O. , Vieweger W.
Published: July 2007

Die Breite magnetischer Streifendomänen in CrBr3 und CrJ3 wurde lorentzmikroskopisch zwischen der Curietemperatur und 4 °K bestimmt. Bei tiefen Temperaturen ist die Breite fast konstant, nimmt aber bei Annäherung an die Curietemperatur plötzlich ab. Dieses Verhalten kann durch die übliche Domänentheorie und unter der Annahme A ∼ I gedeutet werden. Hexagonale Domänen wurden nach Anwendung eines Feldes senkrecht zur leichten Achse beobachtet.
Die Bestimmung der Fermifläche von Kadmium aus der Orientierungsabhängigkeit der Periode der Sondheimer‐Oszillationen
Authors: Schwarz H.
Published: July 2007

An einem hochreinen Kadmiumeinkristall mit Widerstandsverhältnis ϱ273 °K/ϱ4,2 °K = 18000 wurden bei 4.2 °K Sondheimer‐Oszillationen in der Feldabhängigkeit des Hallwiderstandes in ihrer Abhängigkeit von der Kristallorientierung gemessen. Die Ergebnisse zeigen, daß der linsenförmige Teil der Fermifläche in der dritten Zone für die an Kadmium beobachteten starken Sondheimer‐Oszillationen verantwortlich ist. Es wurde ein Verfahren entwickelt, mit dem dieser Teil der Fermifläche aus der Orientierungsabhängigkeit der Periode der Sondheimer‐Oszillationen sehr genau bestimmt werden konnte. Die so bestimmte Fermifläche ist rotationssymmetrisch um die hexagonale Achse und stimmt mit den Ergebnissen anderer Methoden gut überein. Die Abweichung vom Modell quasifreier Elektronen ist gering.
Pressure Effects on Zero‐Field Resonance. I. Ge3+ in YVO4 and SeVO4
Authors: Hillmer W. , Urban W.
Published: July 2007

The influence of hydrostatic pressure on the zero‐field resonance frequencies of Gd3+ in some isostructural crystals has been measured directly. A short description of the apparatus is given and first results in the range up to 2 kbar are reported.
Study of the Poole‐Frenkel Effect in CdS Single Crystals
Authors: Kirov K. I.
Published: July 2007

An investigation has been made of the electric field dependence of the probability for thermal emission from traps in CdS single crystals using a method described in [10] for the determination of the trap parameters. Levels with depths of 0.42, 0.20, and 0.11 eV and capture cross‐sections of 1.5 × 10−3, 2 × 10−14, and 1.3 × 10−14 cm2 have been studied. At field variations from 103 to 3 × 104 V/cm, the change of the probability for thermal ionization of the traps expected from Frenkel's theory has not been observed.
Ligand Field Theory Formulation of the Optical and Magnetic Properties of U2 Centres in the Alkali Halides
Authors: Hagston W. E.
Published: July 2007

It is shown that a better theoretical formulation of the properties of the U2 centre in the alkali halides is given in terms of ligand field theory rather than the approach usually adopted, which consists of an application of the techniques employed by Gourary and Adrian [5] in their F‐centre calculations. The general features of the present formulation are discussed in relation to experiment, and future experimental and theoretical investigations suggested which should enable the finer details concerning the validity and usefulness of the approach to be elucidated.
Implications of Ligand Field Theory for Substitutional and Interstitial H Atoms and H− Ions in the Alkali Halides and Alkaline Earth Fluorides
Authors: Hagston W. E.
Published: July 2007

It is shown that the model developed for the U2 centre in the alkali halides [1] is qualitatively successful in accounting for the magnetic properties of substitutional and interstitial hydrogen centres in the alkaline earth fluorides. An interconnection between the present theory and that required in the theory of the hyperfine interaction of F centres in these compounds is also pointed out, as well as a suggestion for utilizing the Löwdin orthogonalization technique as a means of quantitatively estimating covalency effects for the various shells of ligands next to a hydrogen impurity. Following a discussion of the properties expected for U3 centres in the alkali halides, certain possible anomalies in the recent assignment [2] of ESR data to such a centre are pointed out. Finally the optical absorption spectra of U centres are investigated and attention is drawn to the fact that a combination of odd parity vibrations, odd harmonic crystal field components, and covalency effects can make allowed s → s and s → d one‐electron dipole transitions in addition to the usual s→p transitions. The resulting implications are briefly discussed.
Average Atomic Displacements for Lattices with Inversion Symmetry
Authors: Shukla R. C. , Muller E. R.
Published: July 2007

The thermal average of atomic displacements of a crystal lattice is obtained through the use of thermodynamic Green functions. It is shown that this thermal average is zero for lattices with inversion symmetry.
Directional Dependence of Extraordinary Infrared Oscillator Parameters of Uniaxial Crystals (I)
Authors: Merten L. , Lamprecht G.
Published: July 2007

The validity of the classical dispersion relation (resonance terms of Lorentzian type) for the reststrahlen range of the extraordinary ir spectrum may also be rigorously verified from the basic equations of lattice dynamics combined with the Maxwell equations. The parameters occurring in the dispersion equations, viz. ϵ∞ (ϑ) (high‐frequency dielectric constant), ωj(ϑ) (dispersion frequencies), 4πϱj (oscillator strengths), and γj(ϑ) (attenuation constants), become however orientation dependent, where ϑ is the angle between wave vector and optical axis. Explicit formulae may be given for the orientation dependence of these parameters. As an example the orientation dependence, especially of the oscillator strengths (neglecting attenuation) of α‐quartz, are calculated numerically and discussed in detail. Recently Onstott and Lucovsky have been investigated experimentally the orientation dependence of oscillator strengths of α‐quartz for two of the branches systematically. In consideration of a first comparison the agreement with the values calculated is very satisfactory.
Transmission Electron Microscopy of Point‐Defect Clusters in Neutron‐Irradiated Metals. I. Copper
Authors: Rühle M. , Häussermann F. , Rapp M.
Published: July 2007

Neutron‐irradiated copper has been investigated by means of transmission electron microscopy. The nature of the point‐defect clusters has been determined using stereo microscopy. It is shown that the large defects are predominantly of interstitial type and the small defects of vacancy type. The densities and size distributions of the defects observed in differently pre‐treated and irradiated foils were compared. It was found that only quantitative differences exist. Annealing experiments showed that the defect type and the size distribution of the defects are influenced by the annealing atmosphere.
Interpretation of Self‐Diffusion and Vacancy Properties in Silver
Authors: Mehrer H. , Seeger A.
Published: July 2007

Recent measurements of the tracer coefficient of self‐diffusion in silver by Rothman, Peterson, and Robinson are analysed. In conjunction with the data on the equilibrium concentration of vacant sites by Simmons and Balluffi, with the temperature dependence of the isotope effect of self‐diffusion and with quenching experiments a consistent set of vacancy properties is deduced. In the usual notation the following mono‐ and divacancy properties are obtained: E = 0.99 eV, E = 0.84 eV, S = 0.5 k, v≈4 × 1013s−1, E − E = 0.34 eV, and ΔS2v ≈ 2.6 k. These values are in good agreement with annealing experiments.
On Temperature Relaxation in Metals
Authors: van den Sype J.
Published: July 2007

The method of Corbino for measuring the specific heat of metallic filaments is extended to the case where the sample undergoes internal transformations. The resistance oscillations of the ac heated filament are described in terms of a frequency dependent heat capacity and temperature coefficient of resistivity. The theory is applied to vacancy relaxation in metals where the method yields an equilibrium determination of vacancy concentrations and lifetimes. The experimental results of Kraftmakher on the high temperature heat capacity of metals are reinterpreted in light of the present theory.
Light Emission from Impurity Centres and Urbach's Rule
Authors: Lubchenko A. F. , Dudkin S. I.
Published: July 2007

An investigation is made of the shape of the emission spectra due to impurity centres in a solid, taking into account the variation of its quasi‐elastic constants during the phototransitions. A formula for the short‐wavelength edge of the emission spectrum similar to the Urbach expression for absorption is obtained.
An Internal Friction Investigation of Gold‐Rich Gold–Iron Alloys
Authors: Mynard B. A. , Leak G. M.
Published: July 2007

The internal friction properties of five gold‐iron alloys on cooling from 900 °C have been studied. The parameters QR, Δm, τ0, β, and Tp for the Zener peak, which was observed in all the alloys at approximately 400 °C, are discussed. Welch's theory is used to predict values for QD in the alloys. An explanation is given for the observed decrease in Δm on increasing the solute concentration in the two‐phase region; the precipitate is identified as iron. An increase in damping is observed on cooling through the phase boundary; a qualitative explanation is given for this effect.
A Theory of Nonlinear Ultrasonic Wave Amplification in Piezoelectric Semiconductors
Authors: Wonneberger W.
Published: July 2007

A theory of nonlinear acoustoelectric wave amplification in an active piezoelectric semiconductor is presented assuming a sinusoidal piezoelectric potential. An analytic solution is obtained for the complex amplitudes of the electron density modulation. From this closed expressions for the nonlinear gain, the renormalized sound velocity, the harmonic generation, and the current saturation are derived and discussed.
Structure magnétique du spinelle antiferromagneétique ZnFe2O4
Authors: Boucher B. , Buhl R. , Perrin M.
Published: July 2007

On a fabriqué et étudié par diffraction de neutrons un échantillon de ZnFe2O4. Ce corps est un spinelle normal. A 10,6 °K l'ordre antiferromagnétique à grande distance s'établit. La maille magnétique (a, a, 2 a) a un volume double de celui de la maille chimique (a, a, a). Trois modèles de structures magnétiques rendent compte des résultats expérimentaux. Les moments sont dirigés suivant les axes [100] et [010]. A 4,2 °K le moment magnétique du Fe3+ est 4,0 μB. On détermine la variation de la valeur du moment en fonction de la température.
Temperature Dependence of the Structure of Liquid Mercury
Authors: Waseda Y. , Suzuki K.
Published: July 2007

X‐ray diffraction patterns have been obtained from liquid mercury at −35, 15, and 80 °C. The structure factors obtained are nearly independent on temperature and applied to a discussion of the electrical resistivity using Ziman's [16] theory and the pseudopotential (Animalu and Heine [19] or Evans et al. [18]).