bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency conversion of electromagnetic radiation in polar semiconductors
Authors: Belyantsev A. M. , Kozlov V. A. , Trifonov B. A.
Published: July 2007

The non‐parabolicity contribution of the conduction band and the hot electron effect to the non‐linear susceptibility of n‐type InSb at T = 77 °K are compared using the displaced Maxwell distribution function. Electron scattering on the optical phonons and impurities are taken into account. It is shown that at high frequencies the non‐linear susceptibility is due to the non‐parabolicity of the conduction band.
Electronic specific heat of heavily doped semiconductors in a weak magnetic field
Authors: van Cong H. , Mesnard G.
Published: July 2007

The electronic specific heat at low temperature, in a weak magnetic field, is calculated from a simplified model of heavily doped semiconductors. The treatment is based on the Green function methods applied to disordered systems developed in a previous paper. Two important cases concerning the relation between the carrier and the donor concentration are discussed.
Morse function description of anharmonicity in pressure‐volume relations of cubic metals
Authors: Milstein F.
Published: July 2007

The Morse function, Φ(r) = D(e − 2e), is often used to represent interatomic interactions in investigations of a wide variety of physical phenomena. In view of the wide‐spread use of this function, it is of interest to investigate quantitatively the extent to which experimentally determined anharmonic behavior is exhibited by solids with Morse function interatomic interactions. Numerical values of the Morse parameters D, α, and r0 are determined for a number of cubic metals from experimental values of the lattice constant and the elastic moduli C11 and C12. Morse parameters are then used to compute theoretical pressure‐volume (P‐V) behavior, and comparisons are made with P‐V data determined from shock‐wave measurements. Prior studies by other authors have indicated that the Morse function representation of anharmonic effects in metals is satisfactory; however, the present study shows that this representation, in general, becomes fairly poor for pressures which are large enough to produce considerable non‐linearity in the experimentally determined P‐V behavior.
Analysis of the two‐rand hall effect and magnetoresistance
Authors: Kwan C. C. Y. , Basinski J. , Woolley J. C.
Published: July 2007

The variation of the values of Hall coefficient R and resistance ϱ as a function of magnetic field B is analysed for the case of an n‐type semiconductor with electrons in two different sets of conduction band minima. It is shown that both ϱ0/Δϱ and R0/ΔR should be linear functions of B−2 and that the parameters of the separate bands can be determined from the slope and intercept values of such graphs. The appropriate choice of experimental parameters to ensure the required accuracy of band parameters is discussed.
Microscopic theory of lattice dynamics for ionic crystals II. The contribution of long‐range three‐centre potentials to the phonon dispersion of alkali halides
Authors: Zeyher R.
Published: July 2007

The Heitler‐London expression for the cohesive energy of an ionic crystal contains long‐range three‐centre potentials in the S2‐approximation. Their contribution to the dynamical matrix is examined in terms of q‐dependent charge tensors and numerically calculated for six alkali halides, using self‐consistent free‐ion wave functions and a special multipole expansion. Especially numerical values are given for the three‐centre contribution to the elastic constants and for the longitudinal and transversal effective charges at q = 0. The parameters of a simple shell model are fitted to macroscopic data with and without the inclusion of the three‐centre terms. The corresponding phonon frequencies are compared. It turns out that the usual simple shell model is able to simulate the three‐centre contribution to a large extent by a suitable choice of the parameters. Therefore it is found that an explicit treatment of the three‐centre terms in the phenomenological models doesn't lead to a remarkable improvement.
Energy band structure of semiconductors with the space group D
Authors: Morgan D. J.
Published: July 2007

The energy band structure of semiconductors with the space group Dis investigated using as a starting point results of pseudopotential calculations of the energy band structures of GaAs and Gap. The changes in the energy bands which take place when one goes from the zineblende to the chalcopyrite structure are illustrated, and the arrangement of valence and conduction band states near κ = (0, 0, 0) in the first Brillouin zone of the chalcopyrite structure is discussed. The results indicate that the top two valence bends of a semiconductor with the chalcopyrite structure cross. This suggests that for a particular photon energy the absorption coefficients for radiation polarised parallel and perpendicular to the tetragonal axis might become equal in value.
Acceptor states in tellurium
Authors: Marx R. , Nimtz G.
Published: July 2007

Recently acceptor levels due to chemical impurities in tellurium were calculated. Here we present experimental results of the Hall coefficient measured in low magnetic fields between 1.4 and 77 K. The acceptor concentration of the investigated crystals was 1015 cm−3. The observed dependence of the Hall coefficient on temperature can be explained, assuming two acceptor levels above the valence band. This is in agreement with the data predicted by theory.
Excitonic absorption coefficient in semiconductors
Authors: Glinskt R. G. , Song K. S. , Woolley J. C.
Published: July 2007

A criticism of Elliott's model of the excitonic absorption coefficient has been made in a recent paper by Auvergne and Camassel. They proposed a model in which the electron‐hole interaction is neglected for the continuum states. This criticism was based mainly on an alleged discontinuity in the exciton envelope function between the discrete and continuum spectra. In the present paper it is shown that in fact, no such discontinuity exists and the electron‐hole interaction should not be ignored in the continuum. Elliott's model is correct within the specified limitations and, appropriately broadened, gives quite satisfactory agreement with the experimental data.
Infrared impurity absorption in n‐type silicon carbide
Authors: Dubrovskii G. B. , Radovanova E. I.
Published: July 2007

The light absorption in the range 2 to 65 μm has been measured in 6H, 15R, and 27R SiC polytypes at 80 and 300 °K. It is shown that at 80 °K there is a broad absorption band in the infrared spectra of each polytype which is associated with electron transitions from the donor level to the conduction band. From the energy position of these bands values of the activation energy were estimated as follows: ΔE = 0.1 eV (6H SiC), ΔE = 0.05eV (27R SiC), and ΔE = 0.04 eV (15R SiC). From the analysis of the fine structure of the absorption in GH SiC at liquid nitrogen temperature three ground levels of the donor impurity in 6H SiC were obtained: two nearly coinciding with the activation energy of about 0.1 eV and one with the activation energy 0.15 eV.
Ionic conductance of silver sulphide and diffusion mechanism of silver ions in α‐Ag2S
Authors: Bartkowicz I. , Mrowec S.
Published: July 2007

Cationic conductance of silver sulphide has been measured in the temperature range 200 to 440 °C, using silver iodide as an electron blockade. Making use of these measurements the self‐diffusion coefficients of silver in α‐Ag2S have been calculated. Comparison of these data with the results of radio‐isotopic studies reported by Allen and Moore and application of the correlation theory have shown that diffusion of silver in α‐Ag2S proceeds according to the collinear interstitial mechanism.
Determination of optical interband transitions in crystalline quartz from X‐ray spectroscopical data
Authors: Klein G. , Chun H.‐U.
Published: July 2007

For the interpretation of the imaginary part ε2(ω) of the dielectric constant of a solid usually determined from the optical spectra, one can successfully use X‐ray emission spectra and the near‐edge region of X‐ray absorption spectra. This is shown in the case of crystalline quartz. From the X‐ray spectra of this substance conclusions are drawn about the density of states in the valence and conduction band. The possible vertical interband transitions resulting from these conclusions agree very well with maxima in the transition strength ε2(ω) ω2 determined from optical measurements. Furthermore it is demonstrated that the sharp peak at 10.4 eV must be due to an exciton transition in agreement with conclusions drawn from the optical spectra.
Lattice dynamics of highly polarizable homopolar crystals with diamond structure
Authors: Kress W.
Published: July 2007

A modified shell model taking into account the isotropic deformation of the charge density is presented. In contrast to the usual 11‐parameters shell model which has to be fitted to inelastic neutron scattering data, the modified shell model needs only six parameters, five of which are related in a unique way to the macroscopic data (elastic constants, Raman frequency, dielectric constant) and the sixth may be obtained from the infrared absorption data. Therefore the modified model is mainly independent from the inelastic neutron scattering results and its parameters are related in a physical way to the macroscopic constants.
The optical constants of CsI in the excitonic region
Authors: Lamatsch H. , Rossel J. , Saurer E.
Published: July 2007

Measurements of the optical constants n(λ) and k(λ) of CsI in the excitonic region are reported. The reflection and the intrinsic luminescence excitation spectra are calculated for bulk crystal and thin crystalline films and compared to the measured spectra.
Localized electrons and their interaction with the local modes in the electrical conduction in metals
Authors: Dubey S. K.
Published: July 2007

In a previous paper the problem of the non‐magnetic impurities in metals has been discussed and the deviations from the Matthiessen relation have been calculated. However, the effect of localized modes was not considered there. In the present paper a more general theory which includes the effect of local modes has been presented. The problem of the localization of the electrons has also been discussed.
Electron spin resonance in As‐doped Ge in a wide range of impurity concentration
Authors: Gershenzon E. M. , Pevin N. M. , Fogelson M. S.
Published: July 2007

Electron spin resonance of As donors in Ge has been investigated in the impurity concentration range 1.5 × 1015 to 2 × 1019 cm−3 at temperatures from 1.7 to 4.2 °K. Impurity conduction in the same samples has been studied for NAs ≦ 2 × 1017 cm−3. It is shown that the line‐narrowing in the concentration range 2 × 1017 cm−3 ≧ NAs ≧ 4 × 1016 cm−3 with H0 ∥ [100] orientation cannot be due to the electron motion over impurity centres. Exchange‐narrowing due to the formation of clusters has been discussed. The reduction of angular dependence of the linewidth ΔH with increasing temperature is ascribed to transitions into excited states, by which contributions from different valleys to g‐factor are averaged. For highly doped samples the rate of intervalley transitions has been estimated from the data on angular dependence of ΔH.
Analytic formulation of molecular lattice dynamics based on pair potential functions
Authors: Pawley G. S.
Published: July 2007

On the assumption that molecular interactions can be expressed as a sum of atom–atom interactions, the lattice dynamics of molecular crystals has been formulated analytically. The case where molecules occur on crystal sites of opposite handedness has been considered. The presentation lends itself readily to computer programming.
Optical properties of amorphous III–V compounds. I. Experiment
Authors: Stuke J. , Zimmerer G.
Published: July 2007

From reflectivity measurements ε1 and ε2, the real and imaginary part of the dielectric constant, of the amorphous III‐V compounds InSb, InAs, InP, GaSb, GaAs, and GaP are determined in the fundamental absorption region up to 12 eV. Compared with the corresponding curves of the crystals, the spectra of the disordered materials are smeared out and shifted to lower energy. This shift leads to an increase of ε1(0). In the energy region of the E2‐peaks a selective decrease of ε2 is observed. The results for ε2 are briefly discussed in terms of structural properties, and a modified Penn model is applied to the spectral dependence of ε2.
Optical properties of amorphous III–V compounds. II. Theory
Authors: Kramer B. , Maschke K. , Thomas P.
Published: July 2007

Two methods have been used to calculate the ε2‐spectra of amorphous IV‐IV and III‐V semiconductors: The “Complex‐band structure” (CBS‐)method and the “non‐direct transition” (NDT‐)method including energy dependent matrix elements. Both methods start with the calculation of the electronic properties of the corresponding crystals. Results for amorphous Ge, Si, GaP, GaAs, GaSb, InP, InAs, and InSb are compared with experimental ε2‐spectra.
Zur Kinematik von Disklinationen
Authors: Günther H.
Published: July 2007

Die nichtlineare Statik der Disklinationen wurde unter Verwendung eines vierdimensionalen Formalismus zur nichtlinearen Kinematik verallgemeinert. Die Disklinationsströme können dabei in weitgehender Analogie zu den Versetzungsströmen eingeführt werden. Es zeigt sich, daß eine Bewegung von Disklinationen i. a. mit der Erzeugung bzw. Vernichtung von Versetzungen verbunden ist, was einen wesentlichen Einfluß auf die realen Bewegungsmöglichkeiten von Disklinationen haben wird.
Neutron diffraction study of the magnetic structure of Mn3B4
Authors: Neov S. , Legrand E.
Published: July 2007

From the neutron diffraction measurements it is concluded that below the Néel temsperature of 392 K the intermetallic compound Mn3B4 becomes antiferromagnetic. At this stage only the Mn(2c) atoms are magnetic. Below 226 K the Mn(4g) atoms also become magnetically ordered and deform the collinear antiferromagnetic structure to a spiral structure, with an angle of 157.5°, which at lower temperature gradually develops to a collinear antiferromagnetic structure again. The saturated magnetic moments are 2.92 μB for the Mn(2c) atoms and 0.44 μB for the Mn(4g) atoms.
Magnetic properties of NiCr alloys
Authors: Besnus M. J. , Gottehrer Y. , Munschy G.
Published: July 2007

New magnetization measurements on NiCr alloys are reported. At increasing Cr concentrations c less than 11 at%, the mean atomic moment M0 = 0 for c = 12 at% Cr. In the critical concentration range, 11 < c < 15 at% Cr, the experimental data are analysed in terms of the itinerant band model of very weak ferromagnetism. Several characteristic properties related to the effective exchange interaction and to the band structure near the Fermi level are deduced from this analysis.
Optical spin orientation of non‐equilibrium electrons in GaAs and GaAsAlAs solid solution
Authors: Dzhioev R. I. , Fleisher V. G. , Kanskaya L. M. , Ninu O. A. , Zakharchenya B. P.
Published: July 2007

The results of optical orientation investigation of electron spins in semiconductors excited by circularly polarized light are reported. The occurrence of orientation is due to the presence of spin‐orbit splitting of the valence band. The effect has been investigated by measuring the degree q of circular polarization of the recombination radiation and has been observed in GaAs crystals and the solid solution GaAsAIAs. The dependencies of q on the wavelength of the exciting light have been obtained at 77 and 4.2° K. It has been found that in the case of GaAs crystal E increases and on the contrary, decreases in the solid solution, with temperature decreasing from 77 to 4.2 °K. Depolarization of radiation in an outer magnetic field has been investigated and the lifetimes T of nonequilibrium carriers and the times of spin relaxation τs, are determined. For the GaAs crystal τ (77 °K) = (1.4 ± 0.2) × × 10−10 s and τs (77 °K) = (2.8 ± 0.6) × 10−10 s is found. These values increase with decreasing temperature and at 4.2 °K become equal to (2.4 ± 0.3) × 10−10 s and (8.0 ± 1.5) × × 10−10 s, respectively. In the case of GaAs‐AIAs t and T, have been found with an accuracy determined by the magnitude of the g‐factor.
The electrical properties of the single crystal spinel CoAl2O4
Authors: Matveeva N. G. , Shelykh A. I.
Published: July 2007

The electrical conductivity over the range of 300 to 1300 °C and the thermoelectric force (700 to 1300 °C) have been measured on monocrystalline samples of cobalt aluminate. Calculations were made for the drift mobility; the values of the mobility are shown to be low (10−2 to 10−4 cm2/Vs). The drift mobility increases exponentially with temperature with an activation energy Ea = 0.8 eV. A satisfactory description of transport phenomena in CoAl2O4 can be obtained in terms of the small polaron model.
Energy levels and spectroscopic parameters of some Nd3+ complexes deduced from their solid state diffuse reflectance
Authors: Tandon S. P. , Govil R. C. , Surana S. S. L.
Published: July 2007

The values of Slater‐Condon (F2, F4, F6) and Racah (El, E2, E3) interelectronic repulsion and Landé (ζ4f) parameters and electronic energy levels have been computed from the diffuse reflectance spectra of eight Nd3+ complexes. Configuration interaction parameters (α β, Y(22, 1) and Y(22, 3)) have also been computed for the Nd3+ aquo‐ion. The decrease in the F2 values of the complexes as compared to the free ion is greatest among all the parameters. The bonding parameter b1/2 has been computed from the observed nephelauxetic ratio. The relative variation of covalent bonding in the complexes has been discussed, the effects of the crystalline hosts on the Fk and ζ4f parameters have also been examined.
Magnetic properties of face‐centered cubic Fe65(PtxIr1 − x)35 alloys
Authors: Shiga M. , Kosaka M. , Nakamura Y.
Published: July 2007

The magnetic properties of the disordered Fe65,(PtxIr1 − x)35 alloys with f.c.c. structure were investigated. The alloys are ferromagnetic over a composition range of x > 0.7; the average magnetic moment decreases rapidly with decreasing x deviating from the Slater‐Pauling curve and the Curie temperature also decreases with decreasing r. The alloys show antiferromagnetic behaviour for x < 0.7; the temperature independent susceptibility of Fe65Ir35 alloy implies an absence of localized moments and an addition of platinum causes a strong temperature dependent susceptibility suggesting a formation of localized moments. The magnetic properties of the present alloys are discussed on the base of assumptions on the character of 3d electrons at iron sites.
On the orthogonalized plane wave method
Authors: Abarenkov I. V.
Published: July 2007

The overcompleteness of the system of orthogonalized plane waves and related problems in the OPW method are discussed.
Tenfold d‐electron degeneracy in the Hubbard model and transition‐metal magnetism I. The paramagnetic‐ferromagnetic transition
Authors: Siegel E. J. , Kemeny G.
Published: July 2007

Replacing the simplified s‐electron picture of Penn [a] [4], intrasite d–d interactions are included in the Hubbard model. Choosing k‐space correlation functions to represent the paramagnetic and ferromagnetic states, the tenfold degenerate eigenvalue problem is solved and free energies are calculated self‐consistently for various combinations of the three parameters: bandfilling, direct interaction constant divided by the bandwidth, exchange interaction constant divided by the bandwidth. The paramagnetic‐ferromagnetic phase boundary surface is plotted at near zero and finite temperatures with the third dimension being exchange interaction constant divided by the bandwidth. The near‐zero‐temperature trend shows that the inclusion of exchange, as expected, enhances the ferromagnetic region at the expense of the paramagnetic region. This is exactly opposite to the nondegenerate, t‐matrix result of Caron and Kemeny [6]. Finite temperature calculations show the same trend with increasing exchange, but shift the phase boundary surface so as to decrease the ferromagnetic region.
Excitation of the Cs‐5p core level in cesium halides at 30 K
Authors: Saile V. , Skibowski M.
Published: July 2007

The excitation of the Cs‐5p core level in Cs halides which starts a t about 13 eV was studied by measuring the reflection spectra of evaporated films between 12.5 and 26 eV at room temperature and a t 30 K. Synchrotron radiation was used as a light source. In comparison to the spectra at room temperature new remarkable fine structure was found at 30 K. The very complex spectra are discussed with regard to band calculations including excitons associated with critical points. I n a complementary view the spectra are compared with transitions of the free Cs+ ion. A sideband at the high energy part of the most prominent exciton was observed for every Cs halide. It is, presumably, caused by excitonphonon interaction.
Jahn‐Teller Effect on Transition Metal Ions in Silver Halides III. Interpretation
Authors: Ulrici W.
Published: July 2007

The temperature dependence of the optical absorptions involving orbital dublets (Eg) split by dynamic Jahn‐Teller effect (JTE) (measured on AgCl and AgBr doped with Ti3+, Fe2+, and Cr2+) is discussed. From the results obtained for excited Eg states the linear JT‐coupling parameters and the frequencies of the JT‐active ϵGg mode are derived. These ϵg modes are found to be localized around the impurity ion. It is shown that the small and temperature independent oscillator strength of the transition between the JT‐splitting levels of the Eg ground state (measured on Cr2+) is a consequence of the action of the dynamic JTE. The weak increase of the JT‐splitting ΔE of the Eg ground state with increasing temperature is caused by the temperature dependence of the frequency of the ϵg mode following from the thermal expansion of the crystal.
The Effect of Phonon Heating on Photoelectric Phenomena (II)
Authors: Abakumov V. N. , Schleifstein M. , Yassievich I. N.
Published: July 2007

The effect of phonon nonequilibrium on photoelectric and photomagnetic phenomena is considered in such semiconductor samples, in which phonon energy relaxation is controlled by irradiation into the surrounding medium. The phonon distribution function is calculated in such a sample for the case, that phonon flow and minimum sample dimension are in one direction. A table of formulae determining photoconductivity Δσ and photomagnetoelectric e.m.f. VPM in several physically realizable situations is given.
Molecular Field Theory and Phase Transitions in Partially Finite Spin Systems
Authors: Angelescu N. , Costache G. , Nenciu G.
Published: July 2007

A molecular field model of an homogeneous thin film with free surfaces is studied. The existence of one and only one phase transition, which is of second order, is proved. A study is made of the distribution of magnetization across the film thickness. In the limit of in‐ finite number of layers, a description of the bulk is obtained, which is equivalent to the Weiss molecular field description. The critical temperature of the film approaches the bulk critical temperature as the inverse square of the number of layers.
The Photogradient E.M.F. of Hot Carriers
Authors: Ašmontas S. , Požela J. , Repšas K.
Published: July 2007

Results are presented of the investigation of the hot carriers' photogradient e.m.f., Ufg dependent on the electric field intensity in n‐ and p‐type germanium and n‐type silicon. The rate of change of the photogradient e.m.f. in n‐Ge is found to decrease with an increase of the electric field intensity at fields higher than 5 kV/cm. This is explained by the influence of the higher 〈100〉 minima on heating of electrons. The measurements were carried out at room temperature by a microwave technique. The dependence of Ufg on the electric field intensity is calculated in the electron and hole temperature approximation.
On Determination of the Double‐Force Tensor of Point Defects in Cubic Crystals by Diffuse X‐Ray Scattering
Authors: Trinkaus H.
Published: July 2007

A systematic method is described for determining the double‐force tensor of point defects in cubic crystals by analysing diffuse X‐ray scattering in the immediate vicinity of Bragg reflections (Huang‐scattering). Around a given reciprocal lattice point there may occur three types of isointensity surfaces depending on the symmetry of the defects: the “double‐drop” type (“lemniscatoidal” with two sheets), the “apple‐shaped” type (“lemniscatoidal” with one sheet) and the “single‐bubble” type (“ellipsoidal”). The double‐force tensor of point defects can be determined uniquely from Huang scattering if the defects are all equal and parallel. If the orientations of the defects are randomly distributed over equivalent directions of the lattice, information obtained from scattering intensity allows several double‐force tensors. In this case even three selected points of the reciprocal lattice are sufficient to present all of the information which Huang scattering can give about the structure of the defects.
Some Comments on Kubo and Obata' Treatment of the Orbital Susceptibility of Electrons in Metals
Authors: Hebborn J. E. , Place C. M.
Published: July 2007

The approximate treatment of the orbital susceptibility of a metal due to Kubo and Obata is discussed in relation to the more complete, but more complicated, calculations of Hebborn and Sondheimer and Hebborn et al. A physical interpretation of Kubo and Obata's result is presented and its connection with the more complete expressions established.
Conduction in Narrow Energy Bands
Authors: Monecke J.
Published: July 2007

It is proved that the conductivity in a s‐type band exhibits free acceleration behaviour even in the case of strong electronic correlations. A possible metal–insulator transition can occur as a jump in the mean effective mass and can be calculated from the knowledge of a one particle Green's function. The plasma waves are identified to be the soft modes driving the metal‐insulator transition.
Neutral Manganese Centers at the Anion Site in NaCl
Authors: Ikeya M.
Published: July 2007

Optical and EPR studies are made of atomic manganese centers formed above room temperature in NaCl following previously published work on Mn0‐A, ‐B, and ‐C centers formed below room temperature. Optical absorption spectra corresponding to the EPR spectrum of Mn0‐D and to that of Mn0‐E were found. These bands are located at higher energy than the transition energies of free Mn0 from the ground state 6S to the excited states 6P. The blue shift of the transition energies is explained by the change in the Madelung potentials between the ground and diffuse excited states at the negative ion site assuming that the centers are located at anion sites.
On the Use of the Green's Function Method in Shell‐Model Dynamics
Authors: Ra Ø.
Published: July 2007

An augmented and flexible Green's function matrix is found to provide a convenient recipe for core‐core displacement Green's functions in defective systems comprising deform‐able atoms or ions. The enlarged matrix contains readily accessible information also on the defect‐induced perturbation in the thermodynamic partition function.
Effect of Pressure on the Resistivity of AgAu Alloys
Authors: Edwards L. R.
Published: July 2007

The effect of pressure on the resistivity of Ag1−cAuc solid solutions has been measured up to 4 kbar in the temperature range 4 to 273 °K. Solid and fluid helium were used as the pressure transmitting media. The pressure derivatives of the total resistivity, ϱ−1 dϱ/dP, for the alloys in the concentration range c = 0.1 to 0.9 were observed to be negative and to increase in magnitude with increasing temperature. It is shown that the magnitude and sign of ϱ−1 dϱ/dP is primarily determined by the pressure derivative of the residual resistivity. The volume derivative of the residual resistivity, d In ϱ0/d ln V, was found to be positive and concentration dependent. It is suggested that the influence of the filled d‐bands on the scattering potential is responsible for the behavior of d ln ϱ0/d ln V.
On the Energy of the Hexagonal Frank Loop in Face Centred Cubic Metals
Authors: Gaboriaud R. J. , Grilhé J.
Published: July 2007

The energy of the hexagonal Frank loop is calculated taking into account the dissociation of the partial Frank dislocation surrounding the defect. This energy is compared to those obtained for such classical defects as circular or triangular Frank loops and a tetrahedron of stacking fault. The discussion is made in terms of stacking fault energy, shear modulus, and critical number of precipitated vacancies per defect.
Effect of an Electric Field on the F‐Band in Cesium Bromide
Authors: Grassano U. M. , Margaritondo G.
Published: July 2007

The unrelaxed excited states of the F‐centre in CsBr have been studied by measuring the changes in the F‐band caused by an external ac electric field. The following energy distances from the ground state 1S(Γ1) have been evaluated: (1.911 ± 0.005) eV and (1.945 ± ± 0.005) eV, respectively for the two 2P(Γ8) levels splitted by non‐cubic lattice vibrations; (1.992±0.005) eV for the 2P½(Γ6) level and (2.01 ±0.01) eV for the 2S(Γ1) level. A small substructure of the F‐band, probably due to the cubic lattice vibrations, has also been revealed.
Frequency‐Dependent Relaxation Time in Electron–Impurity Systems
Authors: Šimánek E. , Smith J. Scott
Published: July 2007

A general expression for the frequency‐dependent conductivity of an electron‐impurity system is derived by the method of generalized Langevin equation. The conductivity has the form of the classical Drude formula with complex frequency‐dependent relaxation time derived from the correlation function of the random force. The correlation function of the total force is calculated in the Born approximation. The asymptotic long time behavior of this function indicates that its time integral has a plateau for times larger than the duration of a collision. This result and the absence of the exponential decay enables to define an approximate relaxation time from the total force correlation function calculated in the Born approximation.
Ordinary Magnetoresistance of Heavily Doped Semiconductors at Low Temperatures in a Weak Magnetic Field
Authors: van Cong H. , Mesnard G.
Published: July 2007

The ordinary longitudinal and transverse magnetoresistance of electrons at low temperatures in a weak magnetic field is calculated from a simplified model of heavily doped semiconductors. The treatment which is based on the Green's function methods using Feynman‐path integral formulation, is applied to disordered systems and developed already in five previous papers. Two important cases are discussed within the present model. In the first one, an ordinary n‐type semiconductor is considered, assuming that the carrier concentration is equal to the donor concentration; in the second case, the carrier concentration rises as the third root of the total concentration of impurities.
Inelastic Scattering of Neutrons in Crystals Containing Linear Defects
Authors: Ivanov M. A. , Fishman A. Ya.
Published: July 2007

An investigation is made of the cross section of inelastic neutron scattering in crystals, containing a system of parallel linear defects. The model of the crystal with simple cubic la ttice and equal central and noncentral force constants for interactions only between the ne arest neighbours is used. The linear defects in the crystal are described by a change in the force constants for both the interactions between themselves and between the defect an d host atoms. It is shown that the cross section of the coherent scattering has a maxim um in the spectral distribution at the frequencies of the localized vibrations and of the volume vibrations renormalized by the scattering on the defects. For the cross section of t he incoherent scattering peculiarities appear typical for one‐dimensional crystal lattices.
On the Lattice and Dislocation Mechanism of Colloid Formation in Alkali Halide Crystals
Authors: Tsal N. A. , Didyk R. I.
Published: July 2007

A thorough investigation of F → X conversion in NaCl crystals heat‐treated at different temperatures as well as the results of the high‐temperature X‐irradiation made it possible to conclude that there exist two types of X‐centres which differ in the formation sites. X‐centres localized in the crystal lattice (XL‐centres) are responsible for the absorption band with the peak position at 620 nm, while X‐centres responsible for the 550 nm band are localized along dislocation lines (XD‐centres).
Electron States in Crystals with “nipi‐Superstructure”
Authors: Döhler G. H.
Published: July 2007

A semiconductor with a zigzag‐shaped superstructure potential, caused by the introduction of narrow n‐and p‐doped layers into an intrinsic crystal (“nipi‐crystal”), is considered. For high amplitude and long period of this potential the low lying conduction‐ and the upper valence‐subband states are concentrated around the n‐and p‐layers, respectively. The subbands, as obtained for an idealised mode, neglecting fluctuations of the superstructure potential, are extremely narrow with respect to the direction perpendicular to the layers. Approximative calculations show, that the discrete subband structure should be clearly distinct also if electron‐impurity and electron‐phonon interaction is taken into account. The density of states in crystals with “nipi‐superstructure” is completely different from that in the corresoponding n‐ and p‐doped normal crystals. A non‐equilibrium situation can be quasi‐stable due to the low electron‐hole recombination probality.
Bloch Wave Channeling and Extended Lindhard's Theory
Authors: Kubota Y. , Ohtsuki Y. ‐H.
Published: July 2007

Lindhard's theory for ion channeling is extended to a quantum mechanical formulation, and the “Bloch wave channeling”; is interpreted with the planar continuum potential including inelastic scattering.
Comparison of Cyclotron Resonance Width and Collision Frequency when the Scattering Force is of Short Range
Authors: Raju C. S. , Ching‐Lung Ko M. Wu, , Fujita S.
Published: July 2007

The cyclotron resonance width Γ and the collision frequency ωf owe their existence to the same origin: the electronic transition among energy levels caused by the interaction between electrons and scatterers. By starting with the current correlation formulas and using the connected diagram expansion, both Γ and ωf can be calculated from one and the same collision operator in the case of an electron‐impurity system. By assuming a weak Gaussian potential of a short range, it is explicitly shown that a) Γ is of the same order of magnitude as hωf and b) except in the 'extreme quantum limit' ħω0 ≫ kBT, Γ is a fraction of ħωf and levels off to about 1/4 ħωf.
On Spin‐Lattice Interactions in the Heisenberg Ferromagnet
Authors: Gluck P. , Wohlman‐entin O.
Published: July 2007

The properties of the compressible Heisenberg model are discussed. The spin‐phonon interactions are taken into account by an expansion of the exchange coupling in powers of the atomic displacements. The coupled system of spins and phonons is treated by a series of unitary and Bogolyubov transformations. Expressions are derived for the lowering of the magnetic critical temperature due to first and second derivatives of the exchange integral and for the phonon spectrum as renormalized by the magnetic coupling. The change in the excitation spectrum of the spins at high temperatures induced by the presence of phonons is also found by using Callen's decoupling for the spin propagator in the random phase approximations. Where appropriate, the results are in qualitative agreement with previous work and experiment.
Thermodynamics of Ferroelectric Solid Solutions (I)
Authors: Yurkevich V. E. , Rolov B. N.
Published: July 2007

A generalized Ginzburg‐Devonshire thermodynamic theory is considered in the case of ferroelectric solid solutions in which the dependence of the corresponding thermodynamic potential on the impurity concentration is used. The analytical expressions of a number of physical characteristics are obtained as a function of impurity concentration: the phase transition temperature, the polarization, the dielectric constant, and the heat capacity. The effect of an external electric field on the behaviour of different physical characteristics near the phase transition of the second order is considered as well.
Transport Properties of a Polar Semiconductor in a Quantizing Magnetic Field
Authors: Magnusson B.
Published: July 2007

Momentum distribution functions for electrons are calculated for a polar semiconductor with parallel applied electric and magnetic fields. The derivative of the distribution function has singularities at certain electron energies due to the singularity in the density of states at zero energy. The interaction between the levels leads in some cases to a double hump in the distribution function.
Evidence of Phonon Drag in the Electrical Resistivity of Silver
Authors: Kos J. F.
Published: July 2007

The temperature dependence of the electrical resistivity of four samples of pure silver was measured between 1.4 and 4.2 °K. The variation of resistance could not be satisfactorily represented by the Bloch T5 law. The resistances of the three purest samples were best described by an equation R = A T3 + B T5. According to calculations by Dworin a T3 term may be attributed to the effects of phonon drag. On the other hand the resistivity of the fourth samples which contained 3 ppm of magnetic impurities (about ten times that of the other samples) behaved differently, indicating the influence of Kondo scattering.
The Semiempirical LCAO‐MO Treatment of [NiF6]4− Cluster
Authors: Málek J. , Polák K.
Published: July 2007

A parameter‐free SCCC‐MO calculation including interatomic effects was performed for the ground and the first excited state of [NiF6]4− cluster of crystalline KNiF3. The influence of alternative choices of metal basis functions and particular models of population analysis on the values of crystal field parameter 10 Dq, spin‐orbit coupling constant λcrys, and covalency parameter ϵ was investigated. In contrast to the Wolfsberg‐Helmholz model the above parameters depend significantly on the choice of metal basis functions while the effective charges in the system are nearly the same for a chosen type of population analysis. Based on the performed calculations it is stated that the present method is more efficient than previous semiempirical procedures.
Wall Displacement and Bulging in Magnetization Mechanisms of the Hysteresis Loop
Authors: Globus A. , Guyot M.
Published: July 2007

Magnetization mechanisms related to wall displacement and wall bulging are analyzed using a model previously proposed. In the case of the hysteresis loop, where both these combined mechanisms act, it is shown that the coercive force, the remanence and the shape of the loop, can be determined from the values of the internal field and the grain size. This analysis is experimentally confirmed by the fact that the loops corresponding to several YIG samples can be reduced to a single one. In addition, it is shown that, contrary to a general belief, the coercive force is practically independent of the porosity of the samples.
F‐Centres of Two Types in BaFCl Crystals
Authors: Nicklaus E. , Fischer F.
Published: July 2007

F‐centres in X‐irradiated and additively coloured tetragonal BaFCl single crystals have been studied. An F‐centre at a fluorine site absorbs light polarized parallel to the crystallographic c‐axis in a band at 438 nm and light polarized perpendicular to c in a band at 550 nm. A chlorine F‐centre has a band at 532 nm (E ‖ c) and a double band at 440 nm (E ‖ c). This dichroism arises from the tetragonal surroundings of the F‐centres. The splitting of the double bands is probably due to a dynamic Jahn‐Teller effect. In an X‐irradiated crystal there is a partial transformation of fluorine into chlorine F‐centres. In additively coloured BaFCl predominantly fluorine type F‐centres are formed above 300 °C in thermal equilibrium.
Dependence of Silver Halide Energy Bands on Lattice Constant and Halogen
Authors: Fowler W. B.
Published: July 2007

The mixed basis method has been used to compute the energies of selected electronic states of AgF, AgCl, and AgBr at their normal lattice constants, and in addition AgCl at lattice constants appropriate to AgF and AgBr. From these a fairly clear physical picture emerges regarding chemical shifts, hybridization effects, Madelung shifts, and other effects which determine the locations of various states. Results for AgCl and AgBr at their normal lattice constants compare favorably with earlier calculations and with earlier experiments. More recent optical experiments on these solids by Carrera and Brown appear to be in accord with some of these results. The absorption data of Marchetti and Bottger on AgF are discussed, and it is suggested that the low‐energy peak which is observed arises from a direct forbidden excition at T. Band gap deformation Potentials for AgCl are obtained which are in qualitative agreement with results deduced from stress experiments by Aust and by Brothers and Lynch. Finally, the temperature dependent photoemission reported by Bauer and Spicer in AgCl is discussed with respect to the dependence of various energies on lattice constant.
Spin‐Orbit Coupling in Ions in Crystals
Authors: Lowther J. E.
Published: July 2007

Equivalent operators representing the contribution to the spin‐orbit interaction by the crystal field potential are derived. A quantitative investigation of this effect is made for a single d electron.
The Ferromagnetic After‐Effect at 55 K in Electron‐Irradiated Nickel
Authors: Schaefer H. E. , Lampert G.
Published: July 2007

The ferromagnetic after‐effect (MAE) was measured on high‐purity nickel samples (resistivity ratio RRT/R4K > 2000) that had been irradiated with electrons (2.5 MeV) at 27 K with different doses and subjected to several annealing treatments. It was possible to separate the MAE from annealing effects taking place simultaneously. Taking into consideration annealing measurements of the MAE amplitude and the electrical resistivity published elsewhere, it is concluded that the 55 K‐MAE and the corresponding recovery stages ID, IE have to be attributed to the free diffusion of crowdions.
Dislocation and Disclination Contents of Line Defects
Authors: Dundurs J.
Published: July 2007

The dislocation and disclination contents are defined as integrals of the discontinuities in displacement and rotation taken along the line defect. These quantities allow one to uniquely decompose a discrete line defect into a dislocation and a disclination. Moreover, the results for the discrete line defects suggest a new definition of dislocation density.
The Temperature Dependence of the Absorption Edge in Some Amorphous Semiconductors
Authors: Connell N.
Published: July 2007

The implicit and explicit contributions to the temperature dependence of the absorption edge in some amorphous forms of Si, Ge, GaP, and GaAs are reported. The results are used to test a model in which the valence (conduction) band states in amorphous material are a superposition of crystalline valence (conduction) band states of about the same energy. In the case of the III–V compounds, it is concluded that such a model may be invalid owing to the probable existence of “wrong” bonds.
Influence of Neutron Irradiation at Low Temperature on Internal Friction and Bulk Modulus of Silver
Authors: Chountas K. , Dönitz W. , Papathanassopoulos K. , Vogl G.
Published: July 2007

The internal friction and the bulk modulus of silver were studied after irradiation at 25 K with fast neutrons. The Frenkel defects produced by irradiation cause dislocation pinning and a consequent decrease in the Bordoni internal friction peak. With increasing irradiation dose the bulk modulus first increases, reaches a maximum and then decreases below its original value. The behaviour of the modulus with annealing up to room temperature essentially corresponds to that of the residual electrical resistivity after low‐temperature neutron irradiation. A Frenkel defect concentration cFD gives rise to a relative dielastic modulus decrease ΔG/G which was determined to be ΔG/(GcFD) = −33 ± 9.
Electron Mobility in Ge, Si, and GaP
Authors: Rode D. L.
Published: July 2007

Theoretical calculations of electron mobility in the indirect crystals Ge, Si, and GaP are presented. The model assumes parabolic and spherical conduction band minima and includes piezoelectric, acoustic, polar, Coulomb, and intervalley scattering with appropriate electron‐phonon selection rules in all cases. Fermi statistics are accounted for and no further approximations (e.g. relaxation, trial function) are made, since drift mobility is calculated from an exact iterated solution. Recent selection rules for Si and GaP lead to agreement with experiment and suggest that low‐energy LA phonons are unimportant for intervalley scattering.
Exchange Interactions and Local Field Effects in Exciton Theory
Authors: Stolz H. , Zimmermann R.
Published: July 2007

The role of local field corrections in the linear response of the crystal electron system is investigated using Green's function technique. The macroscopic conductivity can be calculated directly from the solution of a Bethe‐Salpeter equation containing in addition to the screened direct an unscreened exchange interaction, the latter being of pure local field type. The formalism is applied to the Frenkel exciton theory.
Functional Integral Approach for an Extended Hubbard Model: Two‐Centre Coupling
Authors: Albani B. , Goedsche F. , Heber G. , Röpke G.
Published: July 2007

The behaviour of two neighbouring magnetic centres imbedded in an effective energy band is studied with the aid of the functional integral formalism. The model includes the parts of intra‐atomic and inter‐atomic Coulomb interaction which can be written in terms of occupation number operators. Orbital degeneration is not considered. The magnetic susceptibility calculated within the static approximation gives a continuous interpolation between the Pauli‐band susceptibility and the case of two ferromagnetically or antiferromagnetically coupled Ising spins in the atomic limit.
Formation d'images électroniques de monocristaux d'or à basse température
Authors: Renard D.
Published: July 2007

Nous étudions par microscopie électronique (électrons de 100 kV) des monocristaux d'or courbes dont l'épaisseur est uniforme et bien connue. Des mesures directes d'intensité transmise dans l'image en fond clair sont effectuées suivant plusieurs orientations et pour plusieurs épaisseurs. Associées à un calcul de théorie dynamique à n ondes et à un calcul de perturbation, elles permettent de déterminer certaines composantes V'(g) de la partie imaginaire du potentiel cristallin. De ces valeurs à basse température, on peut dissocier la partie due aux phonons de la partie due aux excitations d'électrons individuels. On compare l'effet du processus dǔ aux phonons, à température ambiante et à basse température. Les micrographies et les mesures d'intensité à basse température donnent également des informations sur les potentiels réels et sur l'orientation des monocristaux.
Anisotropic Magnetization and Magnetic Anisotropy Energy of Co—Fe (8 at%Fe)
Authors: Nowicki L. , Aubert G. , Frazao L.
Published: July 2007

Magnetic anisotropy energy and anisotropic magnetization of the non‐magnetostrictive Co—Fe alloy have been investigated between —60 and +40 °C. The anisotropic magnetization exhibits a broad maximum near —30 °C. The influence of surface effects is discussed. A good agreement between the results and literature data concerning magnetic anisotropy energy has been found.