bluuebunny/crossref_metadata_2025 huggingface dataset:
Approximate Consideration of the Wave Function Overlapping in the Heitler‐London Theory for a Crystal
Authors: Ledovskaya E. M. , Petrashen M. I.
Published: July 2007

For complex systems, possessing space symmetry and consisting of a large number of subsystems, “the non‐orthogonality paradox” inherent in the Heitler‐London method is practically solved. A method of summing up the permutations in the expressions for energy corrections is developed, basing on the symmetry of the space arrangement of the subsystems and on introducing a limiting distance for subsystem interactions. This method of summing is illustrated on the example of the alkali halide crystal.
Galvanomagnetic Effects of Metals due to Inelastic and Simultaneous Elastic Scattering
Authors: Clausecker K.
Published: July 2007

The transition probability of electrons due to scattering by phonons is derived in Born's approximation. The Wannier representation is used to characterize the displacement potential by a few matrix elements which are determined by the galvanomagnetic effects. Therefore the Boltzmann equation is solved by the new method of Fourier transformation. For additional elastic scattering of electrons by point defects, questions of Matthiessen's and Kohler's rule are discussed by interpolation formulae referring to numerical results.
Interaction of Rare Gas Interstitials with Lattice Defects in Sr‐doped Potassium Halides
Authors: Felix F. W. , Müller M.
Published: July 2007

Results are presented on Ar diffusion in single crystals of Sr‐doped KF, KCI, KBr, and KI. Ar was homogeneously distributed in the crystals during a neutron irradiation by the reaction K‐41(n, p)Ar‐41. It was verified, that cation vacancies, which were introduced by the irradiation were annealed out when diffusion became detectable, i.e. above 200 °C. Any influence on gas diffusion could therefore be attributed to the divalent doping alone, that is to the consequently introduced cation vacancies. The concentration of these vacancies was determined by measuring the ionic conductivity. In the case of KF, KCI, and KBr but not in the case of KI the gas mobility was reduced with respect to the pure crystals. Thus, the cation vacancies seem to act as gas traps in KF, KCI, and KBr. These effects have been predicted by Norgett and Lidiard [3] on the basis of theoretical calculations of migration and binding energies of mobile Ar interstitials.
Multiple Scattering of Thermal Neutrons by a Perfect Crystal. I. General Foundations
Authors: Lenk R. , Solbrig H.
Published: July 2007

The wave function of a neutron in a regular crystal is built up as a superposition of a primary plane wave and outgoing spherical waves. The elastic scattering properties of the nuclei are given exactly by their complex scattering amplitude f. It is carefully distinguish‐ed between the total wave field and the arriving field at any scattering centre. This results in a correct and consistent description of absorption effects. In the case of an infinite crystal slab the construction of the wave field is simplified by a lattice plane method: all the spherical waves coming out from such an infinite lattice plane add to plane waves, most of them are strongly damped with increasing distance from the plane. The undamped waves give the far‐field, which contains all the interesting informations about the collective interference effects. Neglect of the damped waves gives a good starting point for the approach given in the following two parts of this paper.
Magnetic Properties and the Invar Effect of Iron–Nickel Alloys
Authors: Dubinin S. F. , Sidorov S. K. , Valiev E. Z.
Published: July 2007

On the basis of a unified physical model calculations are made of the concentrational dependence of Curie temperature, the temperature dependence of magnetization, and the invar effect of the iron‐nickel alloys using the effective field method. It is shown that the results are in good agreement with experimental data.
Electron Microscopy Study of the “Direct Resolution” of Periodic Antiphase Boundaries, with Special Reference to Ag3Mg
Authors: Vanderschaeve G.
Published: July 2007

In a long period ordered alloy, interference between superlattice and satellite beams allows to obtain fringe systems, the characteristics of which are analysed within the two beam kinematical theory of electron diffraction. Expressions for the intensity are given in the different cases and fit with electron microscopy observations performed on an Ag3Mg alloy of 22 at% Mg composition. These observations show conclusively that antiphase boundaries occur regularly on every second (100) plane for such a concentration.
The Influence of Sulphur Substitution on the Magnetic Properties of Uranium Monoarsenide
Authors: Leciejewicz J. , Murasik A. , Troć R. , Palewski T.
Published: July 2007

The magnetic properties of the UAs‐US solid solution have been studied using neutron‐diffraction and magnetic methods. The low‐temperature magnetic phase of UAs was found to be stabilized by the addition of sulphur in a wide range of temperatures and compositions. The transition to a ferromagnetic structure of US proceeds through a transient phase. Its magnetic structure has been determined to be of longitudinal static spin wave type with cosinusoidal modulation. Its periodicity is 2.5 a, where a is the lattice constant of a f.c.c. crystallographic unit cell.
Galvanomagnetic Properties and Band Structure of the BiSbAs System
Authors: Shakhtakhtinskaya M. I. , Tomtiev D. S.
Published: July 2007

The galvanomagnetic properties of Bi75–xSb25Asx solid solutions with As concentration up to 3 at% has been measured at 77 °K. The results are interpreted in terms of a two‐carrier multi‐valley band model. It is shown that the axial ratio of the electron and hole ellipsoids in the BiSbAs system is decreased in comparison with pure Bi and Sb. The shape of the Fermi surfaces of the electrons and holes in the BiSbAs alloy system is equal to that of Bi75Sb25.
X‐Ray Coloration of Eu2+‐Doped KCl
Authors: Chowdari B. V. R. , Itoh N.
Published: July 2007

The irradiation effects in KCl doped with Eu2+ have been studied by measuring the optical absorption and EPR spectra. Exposure to X‐rays at room temperature and dry ice temperature leads to a decrease in the intensity of the absorption bands and the EPR lines of Eu2+. The decrease in Eu2+ is partially recovered by F‐bleaching at room temperature. Conversion of the Eu2+ to Eu3+ by trapping a hole at room temperature and dry ice temperature and the conversion of the Eu3+ to Eu2+ by trapping an electron at room temperature is suggested. X‐irradiation at liquid nitrogen temperature produced higher concentration of the Hayes‐Nichols centre than the X‐irradiation at dry ice temperature. This difference in the formation rate of the Hayes‐Nichols centre is attributed to the difference in the Eu2+ concentration at two different temperatures. A plausible model for the Hayes‐Nichols centre is suggested.
Absorption and Emission Spectra of NaCl:Ag Crystals Containing Oxygen and Calcium Impurities
Authors: Kaiser R. , Ludewig K. , Möller W.
Published: July 2007

Optical absorption and emission of NaCl crystals doped with different silver concentrations and containing various contaminations of calcium and oxygen were investigated. The amounts of silver, calcium, and oxygen were determined by neutron activation analysis. Two absorption bands at 250 and 260 nm show the same temperature dependence between 80 and 300 °K as the F centre absorption in NaCl. Silver and oxygen are necessary for the centre, but our data provide no conclusive evidence that calcium is involved. The emission spectrum consists of three distinct bands at 350, 380, and 450 nm, which are interpreted.
Dynamic Susceptibility of an Itinerant Antiferromagnet in a Magnetic Field
Authors: Caillé A.
Published: July 2007

The dynamic susceptibility of an itinerant antiferromagnetic metal is calculated in the random phase approximation in an external magnetic field. The model used applies to metallic chromium below its spin‐flip temperature. The static limit of the susceptibility is obtained for both the long‐wavelength limit and the wave vector Q of the spin density wave. The spin‐wave dispersion relation is obtained for both the above limits.
Sharp‐Line Photoluminescence in Cadmium Telluride
Authors: Noblanc J. P. , Duraffourg G.
Published: July 2007

The photoluminescence spectrum of CdTe has been studied in the 1.4 to 1.5 eV range. New lines have been observed in several samples. The sharp lines are interpreted in terms of annihilation of excitons bound to single, or pairs of, isoelectronic impurities (probably oxygen).
Magnetophonon Resonances in Polar Semiconductors
Authors: Peterson R. L. , Magnusson B. , Weissglas P.
Published: July 2007

The first numerical calculations are reported of electrical transport properties in polar semiconductors in the non‐ohmic regime, for large to intermediate magnetic fields parallel to an electric field. Magnetophonon resonances in such properties as magnetoresistance and acoustoelectric gain are demonstrated. The results obtained generally confirm the hot electron interpretation by Dolat and Bray of their magnetoacoustoelectric experiments in n‐InSb.
Optical Absorption Spectra of Copper Ammonium Sulphate Hexahydrate Single Crystals Diluted with Magnesium Ammonium Sulphate Hexahydrate
Authors: Mathur S. C. , Bansal S. L. , Goel V. P.
Published: July 2007

The optical absorption study on the effect of solid dilution on tutton salts has been extended to the case of copper ammonium sulphate single crystals diluted with magnesium ammonium sulphate, and the change of crystal field symmetry from tetragonal to rhombic, on dilution, has been established.
Piezoresistance and Magnetopiezoresistance of n‐Ge in the [110] Direction
Authors: Baranskii P. I. , Buda I. S. , Dakhovskii I. V. , Kolomoets V. V.
Published: July 2007

The piezoresistance and magnetopieresistance were investigated in n‐Ge (ne = 1.48 × 1013 cm−3) for X ∥︁ H ∥︁ [110] at T = 77 °K (0 ≦ |X| ≦ 6000 kp cm−2; 0 ≦ |H| ≦ 100 kOe). It is shown that in the range of magnetic saturation the longitudinal magneto‐resistance is approximately increased by 10 times when X ∥︁ [110] is altered from zero up to 6 × 103 kp cm−2. On the basis of anisotropic scattering theory the dependences ϱ = f(X), (f)x = f(H), (Δϱ/Δϱ0)x = f(X) (Δϱ/ϱ0)H = f(X) were calculated, using the constants of deformation potentials Eu = 16.4 eV, Ed = −6.4 eV and assuming that the uniaxial deformation results only in the redistribution of the current carriers between relatively shifted energy minima and does not change the shape of the equal‐energy surfaces in n‐Ge. The results of the experiments are in agreement with the theoretical calculations not only qualitatively but quantitatively. The use of some sets of constants Eu and Ed mostly used in modern literature (instead of the ones presented above) for the theoretical calculation of the dependence (Δϱ/ϱ0)H = 50 kOe = f(X) results in a great disagreement between the curves calculated and the experimental data at |X| < 3000 kp cm−2.
The reflection of low‐energy ions from a single crystal simulated by different models
Authors: Karpuzov D. S. , Yurasova V. E.
Published: July 2007

The reflection of argon ions with an energy of 50 to 500 eV from a copper single crystal is simulated on a digital computer. Three models are used to describe the interaction of the projectiles with the crystal: 1. the ion interacts in each moment only with the nearest crystal atom, 2. the ion interacts with all atoms of some microcrystallite whose atoms are assumed to be free, 3. the ion interacts with a microcrystallite of bound lattice atoms. For the Ar+–Cu and Cu–Cu interaction we use the Born‐Mayer potential. A comparison of the results on the spatial and energy distributions of the ions in the different models is made.
General features of field emission from semiconductors
Authors: Baskin L. M. , Lvov O. I. , Fursey G. N.
Published: July 2007

A theory of field emission from p‐ and n‐type semiconductors is developed without use of the zero current approximation. It is demonstrated that in p‐type semiconductors, near the crystal boundary, a weakly conducting region is formed, depleted of mobile carriers which exerts a limiting influence on the current and results in a saturation region appearing in the current‐voltage curve. The saturation current value depends, essentially, on the generation rate of mobile carriers. In n‐type semiconductors this kind of region is not formed, and the phenomenon of saturation arises due to the limited generation rate throughout the whole depth of the sample.
Résonance paramagnétique électronique de l'ion Cr3+ dans la zircone monoclinique
Authors: Bacquet G. , Dugas J. , Escribe C.
Published: July 2007

Les spectres de RPE d'ions Cr3+ introduits dans la zircone monoclinique montrent l'existence de deux types de centres. Ces spectres s'interprètent à l'aide d'un Hamiltonien du second ordre dont les constantes sont les měmes pour les deux défauts. Seule l'orientation des axes propres du tenseur de champ cristallin est différente.
Photoemission studies of MoS2
Authors: Williams R. H. , McEvoy A. J.
Published: July 2007

Measurements of photoelectron quantum yield and energy distributions, under uv irradiation of energy up to 10 eV, have been carried out on single‐crystal MoS2 faces exposed by cleavage in vacuum. The photoelectric work function Φ is found to be (4.55 ± 0.1) eV. The low value of Φ, the slow rise in yield, and the general shape of the energy distribution curves support the band model proposed by Connell et al. [5]. A maximum in the conduction band density of states is located 5 eV above the valence band edge, and structure in the valence band density of states is revealed. These results are compared with those obtained from uv reflectivity measurements.
The slater model and the metal–insulator transition
Authors: Sanders J.
Published: July 2007

A diagrammatic approach is used to show that the Slater model cannot describe an insulator. To obtain insulation, one has to assume that the energy gap is larger than the bandwidth. It is shown that this assumption implies that important perturbation diagrams are neglected. The analysis is based on the Hubbard Hamiltonian.
Kohn's variational method for amorphous conductors
Authors: Gubanov A. I.
Published: July 2007

A new method for quantum‐mechanical calculations of electronic states in a concrete amorphous material is proposed. This method is a modification of Kohn's variational method for crystals. The volume and surface integrals for one cell are replaced by the sum of integrals over all cells and intercellular boundaries. The linear combination describing the wave function in each cell includes terms accounting for the deformation of the cell; thus the correlation between local atomic configuration and electronic wave function is taken into consideration.
Calculation of the electronic energy spectrum for liquid alkali metals by Kohn's variational method
Authors: Gubanov A. I. , Starbunova T. A.
Published: July 2007

Numerical calculations of the electronic energy spectrum of liquid alkali metals — the simplest amorphous conductors — are performed by Kohn's variational method, which was modified for amorphous conductors by one of the authors. Experimental binary atomic distribution functions are used. Diagrams are given for the electronic energy as a function of the average phase difference between neighbouring atoms.
Wigner‐Seitz approximation for the solution of the Ginzburg‐Landau equations
Authors: Ihle D.
Published: July 2007

In the mixed state of type II superconductors the Ginzburg‐Landau equations are solved by means of the Wigner‐Seitz approximation for arbitrary applied magnetic fields between Hc1 and Hc2.
Analysis of the elastic anomalies at the structural phase transition of SrTiO8 near 105 K
Authors: Pietrass B.
Published: July 2007

Expressions are given for the elastic compliances, sij, and the elastic stiffnesses, cij, of the tetragonal phase which have been derived from the phenomenological theory of the phase transition. The discontinuities of the elastic constants at the transition are calculated from the tetragonal distortion and the stress dependence of the transition temperature and compared with those obtained from sound velocity and Brillouin scattering data.
Structure of liquid antimony by neutron diffraction
Authors: Waseda Y. , Suzuki K.
Published: July 2007

Neutron diffraction patterns from liquid antimony have been obtained at 660 and 800 °C. The structure factors are nearly independent of temperature. Comparing the results with the structure of liquid bismuth and the hard sphere model the existence of two structure types in liquid antimony previously indicated seems to be ambiguous. The electrical resistivity was calculated using Ziman's theory [12] and compared with experimental data. From this in the case of liquid antimony the invalidity of the Born approximation in Ziman's theory was found.
Green's functions for anisotropic elasticity
Authors: Mura T. , Kinoshita N.
Published: July 2007

Green's functions describing the elastic displacement caused by a unit force in an infinitely extended anisotropic media are obtained in series form. The series and its derivatives uniformly converge contrary to the Green's functions obtained by previous investigators. The results are applicable to any type of anisotropy. A special example, requiring no computer calculation is given for the case of cubic crystals.
Impurities and intervalence band magneto‐optical transitions in tellurium
Authors: Hardy D. , Rigaux C. , Vieren J. P. , Hau Nguyen Hy
Published: July 2007

Recent magneto‐optical results obtained in the energy range 100 to 170 meV, for ϵ ‖ c and H ⊥ c, are reported and analysed. Transitions of holes from acceptor states and transitions of holes from the first Landau level of the M band to the quantum levels of the M′1 band are identified by investigating the temperature dependence of the magnetoabsorption lines between 2 and 10°K. Calculations of the energies and intensities of the intervalence band magneto‐optical transitions are performed. The comparison of theoretical and experimental data enables one to determine the parameters of the valence band. The fine structure of magnetoabsorption spectra investigated by wavelength modulation technique indicates the existence of several impurity states. The binding energy of the acceptor ground state is estimated to be about 1.4 meV.
On the anisotropy of the exchange interactions in the ion radical salt (TCNQ)2‐3,3 diethyltiaearbocyanine
Authors: Fedutin D. N. , Shchegolev I. F. , Stryukov V. B. , Yagubskii E. B. , Zvarykina A. V. , Atovmyan L. O. , Kaminskii V. F. , Shibaeva R. P.
Published: July 2007

An investigation is made of the crystal structure, electron spin resonance (ESR), and static paramagnetic susceptibility of single crystals of the complex (TCNQ)2‐3,3 diethyltiacarbocyanine (DTC). It is shown that the splitting of the ESR spectra is due to the anisotropy of the g‐factors of non‐equivalent ion‐radical chains of TCNQ. The g‐tensor of a single ion‐radical chain of TCNQ is found to have molecular symmetry (gxx = 2.0026, gyy = 2.0034, gzz = 2.0021; all ±0.0003.) The existence of splitting of the ESR spectra gives evidence that there is no exchange interaction between non‐equivalent chains. However, the measurements of the static paramagnetic susceptibility and the linewidth analysis indicate that the intra‐chain exchange interaction I/K has a large value: 10 to 15°. Thus, our results show that the spin system in the complex (TCNQ),‐DTC is one‐dimensional.
Faraday rotation in amorphous CdGeAs2
Authors: Vorisek V. , Zvára M.
Published: July 2007

Results of Faraday rotation measurements in the region of the absorption edge of amorphous CdGeAs2, at room and liquid nitrogen temperatures are presented. Comparison with the BHL and HLN formulae for the Faraday rotation of crystalline semiconductors yields room‐temperature values of the energy gap of 1.22 and 1.32 eV, respectively. The results are discussed in terms of the generally accepted model of amorphous semiconductors, and the gaps obtained are tentatively assigned to the mobility gap.
Acoustoelectric parametric interactions and other non‐linear effects in a piezoelectric semiconductor
Authors: Ridley B. K.
Published: July 2007

The theory describing departures from linear bchaviour of a single acoustic wave in a piezoelectric semiconductor is extended to include the case of many waves. In addition to the self‐interaction of each wave and the excitation of its associated evanescent mode, there appear in lowest order the three‐wave parametric interactions. Only those parametric intcractions which are phase‐matched are considered. It is shown that the latter consist, of a normal part, obeying the Manley‐Rowe relations, and an anomalous part, associated with the carrier drift, which do not. Coupled with the parametric gain is a velocity shift whose phase is in quadrature with respect to that of the gain. It is pointed out that nonlinear velocity shifts destroy perfect phase‐matching. The down conversion rate maximises at the subharmonic, and the subharmonic generation rate rises with the frequency of pump to a maximum at about 2.3 ωm, where ωm is the frequency for maximum linear gain. In the weak‐activity regime and apart from parametric processes the non‐linear gain is current‐controlled and remains maximised at ωm. Observed frequency shifts may be due to the frequency dependence of the lattice loss as well as that for subharmonic generation.
Treatment of the electronic structure of the F+ centre in some 11‐VI semiconductors in an effective‐charge point‐ion‐lattice approximation
Authors: Wruck D.
Published: July 2007

The ground and first cxcited state energies of the singly electron occupied anion vacancy (F+ centre) in xincblende and wurtzite II‐VI semiconductors are calculated in a point‐ion‐lattice approximation in which the partially ionic binding character of these compounds is accounted for by introducing an effcctive ionic charge. Restricting to the spherically symmetric component of the defect potential and using hydrogenic 1s and 2p trial functions, the energies and the Corresponding Bohr radii of the F+ centre electron are given as a function of the effcctive ionic charge. Taking appropriate values for the effective ionic charge and for the position of the conduction band with respect to the vacuum level, the location of the ground and excited state levels with respect to the conduction band, the optical transition energies, as well as the corresponding Bohr radii are estimated for CdS, ZnS, and ZnO.
Phonon‐induced self‐energy and mass enhancement of electrons in metals
Authors: Teichler H
Published: July 2007

The phonon‐induced energy correction of electrons in metals and the resulting change of the effective mass are formulated by means of localized functions (i.e. generalized Wan‐nier functions). This formulation makes it possible to take into account, in a simple way, the experimentally observed anisotropies of the Fermi surface and the Fermi velocity. The periodicity of reciprocal space is preserved, thus all “Umklapp” processes are included. As an application of this formulation the κ‐dependent mass enhancement parameter λ(κ) is evaluated for Cu. λ(κ) varies from 0.086 (in 〈100〉 direction) up to 0.185 (at the neck of the Fermi surface); the average is found to be 0.15.
On the theory of the electric conductivity of solids in a strong electric field
Authors: Enderlein R. , Peuker K.
Published: July 2007

A theory of the electric conductivity is given for a simple semiconductor model in the presence of a strong electric field including both the heating of the charge carriers and the field‐induced change of the density of states. The conductivity is divided into an interband and an interband part. The intraband part defines the field‐dependent plasma frequency. The interband conductivity vanishes in absence of the strong field and shows an exponential growth as the field is increased. The connection of this result with the Zener tunneling of electrons between the valence and the conduction bands is discussed.
Diffusion and transport in strain gradients
Authors: Frohberg G.
Published: July 2007

The effect of a strain gradient on the drift velocity and the effect of the strain on the migration energy of point defects are deduced in terms of double force tensors associated with the defect in the stable lattice position and the saddle point position. General equations for the force of transport and the migration energy are deduced and discussed for special cases of strains and double force tensors; the relation to relaxation and activation volumes is given.
Influence of impurities on the de haas‐van alphen effect II. Application to point defects in copper
Authors: Hehl W. , Mann
Published: July 2007

A recent theory for the effects of localized defects in metals on the amplitudes and the periods of the de Haas‐van Alphen oscillations is applied to point defects in copper. The parameters characterizing a defect in the employed model are fixed by means of the neutrality condition and the residual resistivity. The calculations of the Dingle temperatures and the changes in period are carried out for the most important extremal orbits on the Fermi surface of copper as given by Halse. The agreement with the available experimental data is satisfactory. The calculated changes in the de Haas‐van Alphen periods are shown to differ not very much from those obtained in the rigid‐band model.
Electron spin resonance on V2O5: Cr3 +1
Authors: Sperlich G. , Jansen K.
Published: July 2007

The ESR spectrum of Cr3 + ions, substituting V5 + ions in V2O5 single crystals, can be described by the conventional spin Hamiltonian with (at room temperature) gx = gy = 1.959; gz = 1.972; D = + 21.077 GHz; E= 0.47 GHz. The unusually strong temperature dependence of the parameter D is compared with that of SnO2 :Cr3 +.
Etude des centres colorés qui apparaissent dans un cristal de chlorure de strontium dope avec un ion alcalin
Authors: Baltog Par I. , Lefeant S. , Houlier B. , Yuste M. , Chapelle J.‐P.
Published: July 2007

Après irradiation aux rayons à B 90 °K, on obtient un signal R.P.E. dǔ à des centres Vk orientés suivant [001] et un spectre d'absorption optique que nous attribuons à des centres Vk, des centres F* perturbés et des associations de centres F. La largeur des raies du signal R.P.E. est attribuée à l'interaction des centres Vk et des cations alcalins. Cette interaction cesse par chauffaée à 160 °K ce qui montre qu'à cette température les centres Vk devienncnt mobiles. Par chauffage, les centres F* perturbés donnnent naissance à des associations, puis cellcs‐ci fournissent des centres F non perturbès. Le modèle proposé rend compte des phénomènes qui ont été observés dans CaF2:Na+ après irradiation aux rayons X.
Thermal Conductivity of Gadolinium Monosulphide
Authors: Khusnutdinova V. , Oskotspii V. S. , Smirnov I. A. , Sergeeva V. M.
Published: July 2007

The thermal conductivity of gadolinium monosulphidc was measured within the temperature range of 80 to 720 °K. The lattice part of the thermal conductivity (XL) mas determined. It is difficult to explain the temperature dependence of xL, theoretically taking the phonon scattering by conduction clcctrons into account contrary to the case of the lanthanum monochalcogenides. The additional lattice thermal resistivity in GdS is attributed to phonon scattering on the paramagnetic statcs of Gd ions in the crystal field.
The inelastic nature of diffuse X‐Ray scattering near the α‐β transition in quartz
Authors: Bauer K. H. W. , Jagodzinski H. , Dorner B. , Grimm H.
Published: July 2007

By inelastic scattering of neutrons, the origin of diffuse X‐ray scattering along [ζ00] directions has been investigated. Phonon frequencies are found to be anisotropic and especially low for the [ζ00] direction. Phonons with low frequencies cause enhanced X‐ray scattering in pronounced diffuse streaks. It is probable that this occurs because a soft optic phonon, which drives the α‐β transition and which has been investigated at q = 0 by other authors, becomes soft very predominantly for the [ζ00] direction and forces down an acoustic dispersion branch. The measured phonons are strongly damped at 560 °C (13° below the transition) so that there is a remarkable tail at zero energy transfer, but elastic scattering as expected from static disorder was not observed. The dispersion for deviations from the [ζ00] direction shows a steep valley, which explains the width of the diffuse scattering perpendicular to the [ζ00] direction.
Studies of photoluminescence in GaAs1−xPx mixed crystals
Authors: Gaj J. A. , Majerfeld A. , Pearson G. L.
Published: July 2007

Photoluminescence measurements on GaAs1−xPx single crystals were performed for the composition range 0.27 < x < 0.44 throughout the spectral region 0.6 < λ < 0.8 μm at temperatures between 5 and 125 °K. Four luminescence bands A, B, C, and D were found. The suggested identification is: B hand‐to‐band transitions, B and C conduction band‐to‐acceptor level transitions, and D distant donor‐acceptor pair recombination. The deep donor level, introduced by S in this composition range, was found to follow the indirect gap variation with composition.
Non‐equilibrium plasma in semiconductors with anisotropic band structure
Authors: Dykman I. M. , Tomchuk P. M.
Published: July 2007

Oscillations of the non‐equilibrium plasma in semiconductors with anisotropic band structure like p‐type Ge are studied. The non‐equilibrium of the plasma is caused by a sufficiently large external electric field. A high‐frequency contribution (due to the field of the oscillations) to the carrier distribution function is found from the kinetic equation taking account the scattering anisotropy and spatial dispersion. The dependences of the frequency and damping constant of the eigenoscillations on the magnitude and orientation of the constant field are determined. A summary of the results obtained and of the proposed experiments is given at the end of the paper.
Jahn‐teller structure in 3A2(3F) → 3T1 (3F) absorption band of CdS:Ti2+
Authors: Boyn R. , Ruszczynski G.
Published: July 2007

The absorption spectrum of Ti2+ centres in CdS betwccn 0.3 and 1.5 eV is measured in the temperature range 10 to 295 °K The spectrum can be explained on the basis of crystal‐field theory. A detailed analysis of the temperature dependence of the 3A2, → 3T1 (3F) band shows that the triplet structure of this band is due to strong interaction with τ2 type vibrational modes of phonon energy 3.3 meV. This analysis is based on the theory of Toyozawa and Inoue [6] and the method of moments of Henry et al. [14]. Effects of the autoionization of the 3T1 state (which has been shown to be located in the conduction band [13]) are believed to be seen at low temperatures.
Anomalous polarisation current in alkali halide crystals
Authors: Harris L. B.
Published: July 2007

In low temperature de polarisation of alkali halide crystals current sometimes flows in the opposite direction to that normally observed. This anomalous current, which is small and not due to electret effect, appears to be a flow of conduction charge in surface layers, observed only when the processes causing conventional polarisation are minimal. The crystal surface acts as though it contains a negative capacitance that stores a layer of anomalous charge, whilst normal charge tends to form peripherally around guard‐ring electrodes. Polarisation is largely a surface effect, having little relation to bulk crystal properties.
Structure magnétique ordonnée du composé DyCu
Authors: Wintenberger Par M. , Chamard‐Bois R. , Belakhovsky M. , Pierre Et J.
Published: July 2007

Le composé DyCu a été étudié par diffraction neutronique sur poudre. Le diagramme observé laisse subsister une indétermination entre une structure colinéaire avec les moments parallèles à un axe quaternaire et une structure non colinéaire avec les moments portés par les axes ternaires. L'étude du champ cristallin, de l'énergie dipolaire et celle de l'effet Mössbauer [1] sont en faveur de ce dérnier type de structure.
Tunable stimulated spin‐flip raman scattering in InSb at various wavelengths
Authors: Irslikger C. , Grisar R. , Wachernig H. , Häfelf H. G. , Smith S. D.
Published: July 2007

Tunable stimulated spin‐flip Raman scattering from conduction electrons in InSb is investigated at four different pump wavelengths (10.6, 10.2, 5.3, 5.1 μm). The tunable frequency range of the Raman‐scattered radiation is increased. Output powers of the Raman‐scattered light as a function of input power densities and magnetic fields were measured for the mentioned pump wavelengths. Thresholds for stimulated scattering were determined. From these the gain factors were calculated. The expected resonance in the 5 μm region is seen in the results and leads to extremely low thresholds and high gain factors.
π‐electron absorption spectra in free‐base phthalocyanine and porphyrin
Authors: Mathur S. C. , Singh J. , Kumar H.
Published: July 2007

π‐electron absorption spectra in the range 14000 to 60000 cm−1, in free‐base phthalocyanine and porphyrin have been calculated using molecular orbitals method. The new transitions beyond the Soret band observed by Schechtman and Spicer [5] and Edwards and Gouterman [6], in phthalocyanines, are explained.
On the effect of overlapping and covalency on the optical spectra of impurity ions in dielectric crystals
Authors: Cherepanov V. I. , Krotkii A. I. , Shchetkov A. A.
Published: July 2007

The influence of overlapping and covalency on the interelectronic correlation parameters of impurity ions with 3dN (N = 2, 3, 7, 8) configuration in octahedral complexes is considered using the MO‐LCAO approximation. It was shown that in addition to a decrease of the usual Slater parameters F0, F2, F4, these effects lead to the appearance of additional parameters. The meaning of these parameters is discussed. Numerical calculations are made for the complexes V3+O, Cr3+F, Ni2+F, Co2+F.
Energy loss of hot carriers due to optical phonons in degenerate nonpolar semiconductors
Authors: Tschulena G. R. , Keil R.
Published: July 2007

An expression is derived for the average rate of energy loss of hot carriers scattered by optical phonons in degenerate nonpolar semiconductors. A discussion of the influence of degeneracy for the particular case of n‐type germanium is presented. The influence of degeneracy on the energy relaxation time is estimated.
Ultrasonic attenuation in p‐Type Gasb at microwave frequencies
Authors: Bougnot G. , Galibert G. , Desfours J. P.
Published: July 2007

An investigation is made of the variation of the attenuation coefficient for shear and longitudinal ultrasonic waves which propagate through monocrystalline p‐type Gasb. The study was carried out for frequencies ranging from 0.5 to 1 GHz and in a range of temperatures from 5 to 300 °K. The measurements made by the pulse echo method are then compared with the theory of Woodruff and Ehrenreich and that of Bommel and Dransfeld.
Magneto‐optical anisotropy in nickel
Authors: Parker M. R.
Published: July 2007

The permittivity tensor normally employed in macroscopic magneto‐optical theory of magnetic media, based solely upon considerations of the effects of spin–orbit coupling, is inadequate in providing a complete theoretical description of the magneto‐optical behaviour of single crystal nickel. It is shown here that the observed dependence of its magneto‐optical behaviour on crystallographic orientation can be explained satisfactorily by considering, in addition to the effects of spin–orbit coupling, the anisotropic effects of magnetostriction on the optical constants of the medium.
ENDOR investigations of Cr+ centres in NaF, NaCl, and NaBr
Authors: Ziegler H.
Published: July 2007

Isolated paramagnetic Cr+ centres in sodium halide crystals are studied by EPR and ENDOR. They show cubic symmetry. Superhyperfine and quadrupole interactions with many neighbouring ions (up to 〈300〉 in NaF) could be determined. The experimental results are interpreted in terms of two models for the wavefunction of the centre: overlap and covalency. A new way for the experimental determination of the coefficients for σ‐ and π‐covalency, using the isotropic superhyperfine interactions of neighbours 〈110〉 and 〈200〉, is proposed. The small anisotropic superhyperfine interaction of the nearest neighbours, which becomes even negative for Br− in NaBr, cannot be understood along these lines.
Mössbauer spectra of 57Fe in Fe1−xCoxSi and Fe1−xNixSi
Authors: Dubovtsev I. A. , Sidorenko F. A. , Bortnik A. N. , Shubina T. S. , Filippova N. P.
Published: July 2007

Mössbauer spectra of 57Fe in Fe1−xCoxSi and Fe1−xNixSi have been investigated as a function of composition and temperature. Substitution of Fe by Co and Ni increases the isomer shift throughout the temperature range studied. Composition dependence of the quadrupole splitting correlates reasonably well with similar dependences specific to other physical characteristics of these alloys. Rise of temperature is accompanied by a decrease of quadrupole splitting in the range of temperatures involved. The results of the study are used to discuss the type of energy band.
Self‐diffusion of cesium‐134 and diffusion of rubidium‐86 in cesium iodide single crystals
Authors: Klotsman S. M. , Polikarpova I. P. , Timofeev A. N.
Published: July 2007

The self‐diffusion of Cs‐134 and the diffusion of Rb‐86 in CsI single crystals were measured in the temperature range 404 to 603 °C using the tracer‐sectioning technique. The temperature dependencies of diffusion coefficients are D = (17.6) exp [−(35460 ± 140)/RT] cm2 s−1 for Cs‐134 and D = (27.3−2.7+3.0) exp [−(34540 ± 160)/RT] cm2 s−1 for Rb‐86. Comparison of present data with earlier results on diffusion parameters of Na‐22 in CsI single crystals shows that there is no dependence of the activation energy Q on characteristics of the homovalent impurities. On the other hand, the pre‐exponential factor D0 increases steadily with decreasing ion radius of the diffusing cations. The independence of Q on homovalent impurity characteristics is in qualitative agreement with known anomalous properties of cations with small ion radii in alkali halide crystals and with the expected temperature dependence of the correiation factor.
Continuum elasticity calculation of the electric field gradient around point defects in KBr and KI
Authors: Muggli J.
Published: July 2007

The strain field in alkali halide crystals containing low concentrations of substitutional alkali or halide ions is calculated with the help of anisotropic continuum elasticity theory using Vegard's rule. The gradient elastic tensor S for KBr and KI is derived from a comparison with experimental shifts of NMR lines. It is found that continuum theory can describe the field gradient at ion sites as near as [300] and [110] as seen from the defect and can explain critical sphere measurements.
Investigation of the stability of the Si III and Ge III crystal structures using force constants
Authors: Weaire D. , Williams A. R.
Published: July 2007

The metastable crystalline phases of Si and Ge, known as Si III and Ge III, offer an interesting test of the force constant models currently being applied to the study of amorphous Si and Ge, since they are made up of distorted tetrahedral bonds. It is found that, using force constants depending only on the bond lengths and angles (adjusted to fit the phonon spectrum of the diamond cubic structure by Singh and Dayal), minimisation of the total energy gives structures and densities fairly close to the observed values for these phases. However, the magnitude of the total energy, relative to the diamond cubic structure, appears to be much too large and some caution seems advisable in applying this or similar models to the calculation of the heat of crystallisation of amorphous semiconductors.
On the effect of irradiation intensity on defect production in pure and iodine‐doped KCl at room temperature
Authors: Goldstein F. T.
Published: July 2007

A study was made of the room temperature coloration of pure and iodine‐doped KCl. Various intensity‐dependent effects were observed. These include the nature of the V bands as well as the shape of the F growth curve.
A perturbation‐theoretical treatment of the time‐dependent Boltzmann equation for crystal electrons in a strong electric field
Authors: Henneberger K. , Röseler J.
Published: July 2007

The properties of the time‐dependent distribution function, particularly the possibility of formation of Zener oscillations, are investigated. Hereby the Boltzmann equation is reduced to an eigenvalue problem. In addition to general investigations, a perturbation‐theoretical method for the calculation of the eigenfunctions and the eigenvalues in the strong‐field limit is given. The restriction to the first terms of the perturbation‐theoretical expansion is allowed, if and only if Zener oscillations exist relatively unperturbed. This is possible for electric field strengths which satisfy the rough condition

Using an exactly solvable but nontrivial model, the results found by general considerations can finally be confirmed and completed.
The theory of the Borrmann dislocation contrast
Authors: Tikhonova E. A.
Published: July 2007

The equations of the dynamical scattering theory are derived for a crystal with slowly varying distortion using a method analogous to the WKB method in the quasiclassical approximation. In the zeroth approximation in h a system of two equations is obtained. The local dispersion equation determines the eikonals of the wave functions. The equation in the first approximation is derived under the assumption that only one function determines the change of the amplitudes. The system of equations is not complete but allows to determine in absorbing crystals the change of the electron current component which extends along the reflecting plane and is principally apparent in the formation of Borrmann dislocation contrast. The obtained equations are valid as well far from the dislocation as close to it. The contrast of screw dislocations parallel to the crystal surface is considered.
Calculated phonon spectra and INS cross sections of MgZn2
Authors: Eschrig H. , Urwank P. , Wonn H.
Published: July 2007

The phonon spectra of the Laves phase of C14 structure (AB2‐type intermetallic compounds) and the inelastic neutron scattering cross section according to the creation and annihilation of phonons are investigated using group theory. For MgZn2 model potential calculations of phonon spectra are made along the line of highest symmetry in the Brillouin zone using Shaw's potential. Very low lying optical branches are found.
The effect of alloying on the energy gap of a semiconductor: Calculations for Pb1−xSnxTe and Pb1−xGexTe
Authors: Wexler G. , Morgan G. J.
Published: July 2007

Simple calculations have been made of the shift in the energy gap in PbTe when alloyed with small amounts of Sn and Ge. The calculated energy shifts, which are of opposite sign for these two systems, are in rough agreement with experiment [1,2]. They are the sums of contributions produced by the strain field, the change in the short‐range potential, and the change in the relativistic energy. A variational method has been used, containing a trial function based on published details of the wave functions in PbTe.
Theory of disordered systems. I. The functional average
Authors: Fischbeck H. J.
Published: July 2007

A theory of disordered systems of noninteracting electrons is derived from the Gaussian functional average over fluctuating potentials. The basic assumption is that the statistical properties of the random potential are solely characterized by its autocorrelation. This theory proves to be formally equivalent to a many‐particle theory with two‐particle interaction, in which the autocorrelation plays the part of the formal interaction. As illustration two simple models are considered. Their density of states, conductivity, and mobility are calculated.
Rotational hysteresis in MgFe and NiFe ferrites with antiferromagnetic precipitate
Authors: Maxim Gh.
Published: July 2007

It is shown that the rotational hysteresis at high fields of the MgFe and NiFe ferrites increases strongly with the concentration of the antiferromagnetic NiO or α‐Fe2O3 precipitate. This influence is explained by the ferrimagnetic‐antiferromagnetic exchange interaction. A new method for evidencing antiferromagnetic precipitates in ferrites is proposed.
Impurity conductivity in low compensated semiconductors
Authors: Efros A. L. , Shklovskii B. I. , Yanchev I. Y.
Published: July 2007

A theory of the temperature and concentration dependence of the impurity conduction in low compensated semiconductors is presented. For the activation energy the expression ε3 = 0.99 (e2/x)N (1 − 0.43 v K1/4) is derived, where ND is the majority impurity concentration, K is the degree of compensation, and v is a numerical factor whose value is likely to be about 0.7. This expression essentially differs from the well known result of Miller and Abrahams. It is shown that the above dependence isin good agreement with available experimental data.
Thermoelectric effects of heavily doped semiconductors at low temperatures
Authors: van Cong H. , Mesnard G.
Published: July 2007

Using the Green function methods, in the Feynman‐path integral formulation, applied to disordered systems and developed already in four previous papers, the thermoelectric effects at low temperatures are studied from a simplified model of heavily doped semiconductors. Two typical cases concerning the relation between the carrier and the donor concentrations are discussed.
Stationary kink motion in the secondary Peierls relief
Authors: Alshits V. I. , Indenbom V. L. , Shtolberg A. A.
Published: July 2007

The problem of stationary kink motion in the secondary Peierls relief has been solved in a self‐consistent procedure. The radiation damping of a kink was studied as a function of its average velocity v and of the relief height. It is shown that at high velocities the kink ernits energy mainly on the basic harmonic, and that the radiation damping is proportional to 1/w. With decreasing velocity v the increase in the degree of non‐uniformity of the kink motion results in a broadening of the radiation spectrum and in the growth of the dissipation. The decrease of the velocity v is possible only up to some critical “starting” velocity below which a stationary kink motion is not realized. A dependence of the starting velocity on the relief height and kink width has been found. The phenomenon of the critical velocity is observed also under conditions of viscous dissipation. In this case the starting velocity decreases with increasing viscosity a and vanishes above some threshold value α. USSRAt α > αc the effect of the “dry friction” type is predicted: With decreasing velocity the dynamic kink damping tends to the static Peierls stress and does not vanish at v = 0. Possible display of the starting velocity effect in the experiment has been indicated.
Theoretically predictable effects and new interpretations in spin wave resonance of thin films with asymmetric boundary conditions
Authors: Puszkarski H.
Published: July 2007

The eigenvalue problem of the finite linear chain with arbitrary asymmetric boundary conditions is solved strictly. The results are used in quantum theory of spin wave resonance (SWR) in thin asymmetric ferromagnetic films. A theory providing some new interpretations of experimentally known effects in SWR and predicting new as yet unobserved effects is proposed. The results are visualized in an especial surface pinning diagram which should prove highly useful for the comparison of experimental data with the theory.
Circular prismatic dislocation loop in a two‐phase material
Authors: Dundurs J. , Salamon N. J.
Published: July 2007

The elastic fields of a circular prismatic dislocation loop in a two‐phase material are evaluated to arrive at the elastic energy and Peach‐Koehler force. The results can be expressed in terms of complete elliptic integrals. The asymptotic forms reveal that the interaction between the prismatic loop and the second phase is not necessarily restricted to simple repulsion or attraction, and that for certain combinations of the elastic constants stable or unstable equilibrium positions are possible.