bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of the Intensity of the Small‐Angle X‐Ray Scattering by Small Clusters of Intrinsic Point Defects
Authors: Kienle W. , Frank W.
Published: July 2007

The small‐angle X‐ray intensity scattered by small platelet‐shaped agglomerates of vacancy or self‐interstitial type is calculated in two ways: within the framework of continuum theory or by a discrete‐lattice model. Both the methods take into account that small clusters are not fully relaxed. A comparison of the numerical results of the two methods is presented for copper. It is found that both the methods lead to results which considerably deviate from those obtained for completely relaxed clusters.
Effective Hamiltonian for the Two‐Dimensional Arbitrary Spin Ising Model
Authors: Sznajd J.
Published: July 2007

A method of the reduction of the generalized arbitrary spin two‐dimensional Ising model to the spin‐half Ising model is presented. The method is demonstrated in detail by calculating the effective interaction constants to the third order in a cumulant expansion for the triangular spin‐one Ising model (the Blume‐Emery‐Griffiths model).
Optical Absorption in Neutron Irradiated GaAs
Authors: Baramidze N. V. , Bonch‐bruevich V. L. , Kurdiani N. I.
Published: July 2007

The spectral dependence is investigated of the light absorption coefficient, α, of GaAs subjected to a fast‐neutron irradiation. In the tail region a complex dependence is found: three parts are seen each of which is described by an exponential dependence of α on photon energy. The experimental results are explained using the concept of random fieldsgenerated by irradiation produced clusters. The statistical characteristicsof the fields are calculated and a quantitative agreement with the experimental data is obtained. Various parts of the spectrum are ascribed to absorption tails due to three kinds of random fields: 1. a deformation potential field due to cluster produced stresses, 2. a smooth field produced by a setof charged clusters in the GaAs matrix, and 3. an intrinsic random field inthe amorphous substance of the clusters.
Impurity Charge Screening in 3d Alloys
Authors: Cser L. , Gladkih I. , Hargitai C.
Published: July 2007

The change of isomer shift and hyperfine field in the first coordination shell of impurity atoms in iron‐based 3d‐metal alloys is discussed from the viewpoint of different charge screening models. It is shown that the change of isomer shift can exactly be described in terms of the asymptotic Friedel model. Interpretation of the hyperfine field change is more difficult and several different models are considered.
Critical Analysis of the Excitation Map Concept for Studying Threshold Effects in VLEED
Authors: Lopez J. , Le Bossé J. C. , Baudoing R.
Published: July 2007

The excitation map concept introduced by Solbrig to discuss threshold effects in very low energy electron diffraction (VLEED) is reinvestigated. In detail the relevance of such excitation maps (| det (1 — M−+R+−)| where M−+ is the reflection matrix of the atomic planes and R+− is the internal reflection matrixof the surface barrier) for characterizing surface resonances in VLEED is examined. It is shown that, in most cases, the use of this concept leads to an overestimate of the resonance contribution in VLEED spectra. The excitation map concept is replaced by a new relevant one. This result is exemplified by reinvestigating the region of Solbrig's excitation map on Ni(001) corresponding to the normal incidence, just below the emergence of the first four diffracted beams (10), (01), (10), and (01). Even in this case, in favour of the resonance interpretation according to Solbrig's analysis, it is shown that the picture of a waveguide located at the surface, channelling the pre‐emergent waves, falls down. This conclusion is strengthened by an analysis of the reflection amplitude matrix of the crystal based upon a second‐order expansion in which the actual role played by resonances can be easily examined. In the case of Ni(001), threshold effects are only due to a simple interference process.
The Voigt Effect under a Strong Electric Field in Semiconductors
Authors: Stramska H.
Published: July 2007

The nonlinear Boltzmann equation is discussed for a strong dc and weak ac electric field. The addition of an energy relaxation approximation to the Boltzmann equation provides analytical expressions for the magneto‐conductivity in high dc electric fields. The nonlinear current density is derived for a strongly degenerate electron gas and for a nondegenerate electron gas. The free carrier Voigt effect in the presence of a strong dc electric field is calculated.
Structure and Vibrational Spectra of a Model of a‐Si:H with Periodic Boundary Conditions
Authors: Winer K. , Wooten F.
Published: July 2007

A ball‐and‐stick model of a‐Si:H with periodic boundary conditions is constructed. A computer replica of the structure is relaxed and the density, radial distribution function, and vibrational spectracalculated.
Solution Enthalpies of Divalent Defects in Alkali Fluorides and Chlorides
Authors: Bandyopadhyay S. , Deb S. K.
Published: July 2007

A method is suggested for finding the Born‐Mayer repulsive parameters of a divalent defect cation in an alkali halide crystal, from the charge density overlap of the interacting ions. These parameters are utilised to calculate the heat of formation of dilute solid solutions of CaCl2, SrCl2 in each of the three alkali chlorides NaCl, KCl, and RbCl and those of CaF2, SrF2 in each of the three alkali fluorides NaF, KF, and RbF following the standard procedure of minimising the lattice energy numerically, as a function of the relaxation of the nearest neighbours, when the defect cation occupies a substitutional position. As known that the calculation of the heat of formation of solid solutions is very sensitive to the proper choice of the repulsive parameters, so these physically plausible calculated values suggest the validity of the method forfinding the solution enthalpies of divalent defects in alkali halides.
An Analytical Theory of FMR in Bulk Metals (Parallel Configuration) III. Surface Impedance
Authors: Fraitová D.
Published: July 2007

A solution of the surface conditions of a ferromagnetic bulk metal for the region of ferromagnetic resonance is presented; the sample in the form of a flat disc is statically magnetized in its surface plane. The assumption of pinned surface magnetization motion (with arbitrary value of uniaxial surface anisotropy parameter and axis normal to the sample surface) is included. The general formulae for the surface impedance are deduced, which agree with the exact numerical calculations of better than 2%.
Mode—Mode Coupling Effects in the Singlet—Triplet Paramagnet in the Vicinity of the Curie Point
Authors: Kowalewski L. , Wojciechowski R.
Published: July 2007

Within the Mori approach the magnetic longitudinal relaxation function in the singlet—triplet model near the Curie temperature is analysed. The influence of mode—mode coupling effects, especially of those of transverse intratriplet excitations, on the long‐time tail of relaxation function and on the line shape of the central mode is also discussed.
Multiple Scattering of Relativistic Electrons under Axial Channeling ina Crystal Model of the Lattice of the Atomic Rows
Authors: Taratin A. M. , Vorobev S. A.
Published: July 2007

Using computer simulation and the lattice model of atomic rows the evolution of the ultrarelativistic electron flux under channeling in the <111> direction in a silicon crystal due to multiple scattering by crystal electrons and nuclei is investigated. It is shown that the electron subtrapping in the bound states takes place in the crystal volume together with the electron dechanneling from the bound states with the atomic rows. A fraction of the particles undergoing the volume trapping is singled out for the first time, and its thickness and orientational dependences are obtained.
Low‐Energy Electron Reflection Intensities from 2HMoS2 as Derived by Scattering Matrix Calculations
Authors: Smith A. E. , Lynch D. F.
Published: July 2007

Results of scattering matrix calculations for the reflection intensities of low energy electrons in the range 0.25 to 15.75 eV are displayed for the layered transition metal dichalcogenide 2HMoS2. An incident energy‐dependent absorption potential based on energy loss data is used. The variation of signal with incident angle is explored and comparisons are made with experimental total current measurements. As with previous work it is concluded that the crystal structure determines the intensity spectrum and that a precise description of the individual scattering events is not necessary.
A Simple Muffin‐Tin Model for Liquid Metals
Authors: Vasvári B.
Published: July 2007

An approximation is developed to the scattering path operator for a topologically disordered system of muffin‐tin potentials. Using the multiple scattering Green's function formalism a simple expression is obtained for the local density of states (LDOS). A heuristic type of averagingprocedure can be chosen which leads to non‐negative LDOS in the conduction band. Numerical results are presented for an s‐resonance model and for liquid 3d transition metals using a self‐consistent crystalline muffin‐tin potential and experimental pair distribution function.
The Absorption Spectrum of Manganate (VI) in BaSO4. A Reinterpretation
Authors: Borromei R. , Oleari L. , Day P.
Published: July 2007

The polarised electronic spectrum of MnO2−4 doped in crystals of BaSO4 is re‐interpreted by making a detailed comparison with the corresponding spectra in the host lattices M2SO4 (M  K, Rb, Cs) and K2CrO4. All bands above 16500 cm−1 arise from charge transfer transitions while the part of the spectrum below 16500 cm−1 is due to theligand field transition e → 2t2. Moreover in BaSO4 the ligand field excited state 2T2(e → 2t2) undergoes a large splitting due to the site perturbation in contrast to K2SO4 in which the splitting is very small. The energies of the charge transfer excited states are only slightly affected by the changeof host lattice. With the new assignments all the ligand field and charge transfer spectra of the d1 tetroxo‐anions MnO2− and CrO3−4 can be interpreted in terms of a common scheme.
Similarity of Ground‐ and Excited‐State Absorption Spectra of Cr3+ Ions in a Strong Crystal Field
Authors: Veremeichik T. F.
Published: July 2007

A comparative analysis of the broad bands of the ground‐ and excited‐state absorption spectra of d3‐impurity ions iscarried out in a point‐ion crystal field theory model. It is found that for d3 electrons in the cubic field (d7 in tetrahedral field) a similarity of these bands should be expected. The similarity results from the particular symmetry of the initial terms of the compared transitions (these terms correspond to the t32 half‐filled shell of the strong cubic field) and from the same orbital symmetry ofthe final state wave functions. Theoretical conclusions are applied to the experimental spectra of Cr3+ ions in ruby, emerald, and MgO. The use of the similarity of ground‐ and excited‐absorption spectra is suggested. The same analysis is carried out for the d2 configuration as well.
Low‐Temperature Lattice Thermal Conductivity of Nonmetallic Solids with Isotopic Impurities
Authors: Gairola R. P.
Published: July 2007

Using thermodynamic Green's function technique, it is shown that the inclusion of anharmonic terms along with the mass and force constant change terms arising due to isotopic impurities in the crystal Hamiltonian, leads to a cross term ΓAD of defect with anharmonic parameters in the expression for the phonon width. This interaction term ΓAD, which varies as DΩ3T, contributes significantly in the vicinity of thermal conductivity maximum, thereby giving a good agreement between theory and experiment, as seen in the analysis for germanium and magnesium stannide solids. A plausible estimate is given for the interaction parameter D taking a linear chain model as example. Due to the occurrence of this interaction term ΓAD, Mathiessen's inverse summation rule no longer remains valid. The present analysis differs from those using Callaway's phenomenological model or extensions thereof, in the sense that it does not explicitly assume the validity of the inverse summation rule in the conductivity calculations, as done by earlier workers.
Pressure Effect on Phonon Frequencies and Elastic Stiffness Constants of Al
Authors: Soma T. , Itoh T. , Kagaya H.‐Matsuo
Published: July 2007

The lattice dynamics of Al under pressure is investigated using the local Heine‐Abarenkov model potential with volume‐dependent parameters in the perturbational method. Then, using the homogeoneous deformation method, the bulk modulus and the shear elastic constants under compression are studied theoretically, and the mode Grüneisen parameters and the pressure‐derivatives of the elastic constants for Al are obtained.
Simulation of Z1‐Oscillations in Low‐Energy Heavy Ion Ranges in Solids
Authors: Chubisov M. A. , Akkerman A. F.
Published: July 2007

The Z1‐range oscillations of low‐energy heavy ions in solids are investigated by computer simulation using an interatomic interaction based on the modified Green‐Sellin‐Zahor potential.
Effect of Cold Work on Hydrogenation of Nickel as Seen in the Thermoelectric Behaviour
Authors: Gupta A. C. , Nigam A. N.
Published: July 2007

Wires of nickel annealed at different temperatures are subjected to cathodic hydrogen diffusion with and without previous cold work. The d‐band shape computed for differently annealed wires are different without cold work, but almost the same after cold work. Thus the cold work distorts the d‐band in differently annealed samples to the same extent.
Coulomb Interaction and Excitons in a Superlattice
Authors: Guseinov R. R.
Published: July 2007

An exact expression is found for the potential of a point charge in a periodic layered system, consisting of alternating layers with two different values of the dielectric constant. The most interesting limiting cases for this potential are considered. Energy spectrum, bound energy, and the ground state radius of the exciton, which is formed by an electron and a hole, belonging to the same layer of the superlattice, are found.
Quantum Corrections to the Screening Length and Anisotropy in Magnetic Field
Authors: Fortini A.
Published: July 2007

The self‐consistent linearized Poisson equation leading to the screened potential of an ionized centre embedded in a free carrier plasma, is rewritten in a closed form taking into account the quantum character of the plasma. Complete resolution in the case of Boltzmann statistics clearly shows how quantum corrections cause a departure of the screening length from its usual semiclassical value. Quantum corrections are also responsible for the anisotropy of the screening in a static magnetic field. Calculations are worked out for the case of a strong quantizing field.
Ultrasonic Attenuation in Liquid Metals
Authors: Vaid B. A. , Sharma K. C.
Published: July 2007

Excess ultrasonic attenuation in general liquid metals, including those contracting on melting, is investigated in the framework of the two‐state model, the thermodynamic theory of relaxation processes, and the recent disorder model of melting proposed by the authors for both types of melts, i.e. those contracting on melting and the others shrinking on freezing. The generalization is affected through a parameter which is solely dependent on the structural consideration, viz. the packing fraction of solid and liquid phase. The agreement of calculated values of bulk viscosity with the experimental data is encouraging.
Electronic Structure and Properties of Cubic Boron Nitride
Authors: Prasad C. , Dubey J. D.
Published: July 2007

The electronic structure of cubic boron nitride without and with fractional ionicity is calculated by the application of the composite wave variational version of the APW method. The main calculations are performed at the high symmetry points Γ, X, and L, and the rest of the band structure is obtained by the tight‐binding interpolation scheme of Slater and Koster. The density of states, imaginary part of the dielectric constant, and the effect of pressure on them are calculated and compared with available experimental and theoretical data.
Refraction Index Variation in the Exciton Resonance of CdS and TlInS2 Single Crystals under Laser Excitation
Authors: Lisitsa M. P. , Stolyarenko A. V. , Terekhova S. F. , Onishchenko N. A.
Published: July 2007

The influence of laser excitation on refraction index variation is investigated for CdS and TlInS2 single crystals at helium temperature. The values of the n variation are obtained in the region of the B‐exciton band for CdS single crystals. Bleaching of the exciton absorption bands is observed due to the Coulomb interaction screening by the carriers generated. The efficiency of Rozhdestvenskii's method of hooks for the analysis of optically induced refraction index variations in the nonstationary case is demonstrated.
Magnetooptical Effects and Optical Absorption of FeBO3 in the Region of 6A1g → 4T1g (4G), 4T2g (4G) Transitions
Authors: Zabluda V. N. , Malakhovskii A. V. , Edelman I. S.
Published: July 2007

The spectra of optical absorption, magnetic linear (MLD) and magnetic circular dichroism (MCD) in the weak ferromagnet FeBO3 are investigated for transitions 6A1g → 4T1g(4G) and 6A1g → 4T2g(4G) at temperatures in the range of 90 to 300 K. It is shown that the temperature dependence of the absorption intensity and the zero moments of MLD and MCD of exciton–magnon lines for the transition → 4T1g is described by an exponent exp (–T/T0) and the MLD of these lines reveal an anomalous temperature dependence. In the region of the transition → 4T2g, where there are no exciton–magnon lines, MLD is not observed at all. The strength of coupling of the exciton–magnon for the transition 4T1g with even vibration Eg is determined and its independence of temperature is shown.
Optical Absorption Studies of Plastically Deformed InSb
Authors: Vignaud D. , Farvacque J. L.
Published: July 2007

Optical absorption studies of edge‐type dislocations are carried out on n‐ and p‐type, weakly doped InSb. Edge‐type dislocations are selectively introduced by means of uniaxial compression at 220 °C. The presence of dislocation induces two main changes in the optical absorption spectra: i) absorption tails just before the band edge, which are associated with the strong internal piezoelectric fields and ii) reduction of the intraband absorption, which are explained by the presence of trapping levels bound to the dislocations.
Three‐Band Model Applied to Narrow‐Gap HgCdTe
Authors: Fau C. , Dame J. F. , de Carvalho M. , Calas J. , Averous M. , Lombos B. A.
Published: July 2007

Hg1–xCdxTe, with x = 0.15 is a semimetal at low temperature (4.2 K) and becomes a narrow‐gap semiconductor at higher ones (77 K). Its transport properties are measured at different temperatures, magnetic fields, and hydrostatic pressures. Based on the measured data, an analytical three‐band model is developed to calculate the concentrations and mobilities of the resulting two types of electrons and one type of holes. The existence of the slow electrons are related to the presence of acceptor states in the conduction band, as it is already elucidated in the case of zerogap HgTe. The concordance of the calculated transport properties, based on this model, with the measured ones supports the subsistence of three types of carriers in the narrow‐gap HgCdTe.
Hopping Conductivity and Electron Localization in Heavily Doped ZnSe
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N.
Published: July 2007

By high‐temperature annealing of the starting high‐ohmic ZnSe crystals (ϱ ≈ 108 Ωcm) in liquid lead or tin low‐ohmic crystals are obtained with specific resistivity from 10−1 to 100 Ωcm. The shallow donor density in these crystals is Nd ≈ 5 × 1017 to 2 × 1018 cm−3. The degree of impurity compensation K ≈ 0.85 to 0.98. The peculiarities of the electric properties of the investigated crystals in the interval from 1.65 to 300 K are interpreted in the frames of a heavily‐doped strongly compensated semiconductor (HDCS) model. In the high temperature region a deep donor level is indicated with a temperature dependent activation energy. It is found that at low temperatures the conductivity exhibits the hopping character following the rule lg ≈ T−1/2. A quantitative comparison of the experimental results with the theory of hopping conductivity in HDCS is presented.
Study of Bonding Configurations in Amorphous GexSi1−x:H Alloys
Authors: Sala D. Della , Giovannella C. , Evangelisti F.
Published: July 2007

The structure of a‐GexSi1−x:H alloys produced at two different substrate temperatures by glowdischarge is investigated over the whole range of the gas composition. By comparing IR spectra and chemical analysis, an overall sticking rate three times larger for Ge than for Si is found, an occurrence which has important consequences on the tailoring of the optical gap Eg. The use of a quasi‐statistical model accounts for the intensity of the stretching bands of several hydrides present in the structure and permits to differentiate among hydrides differing only in the second neighbor atoms.
The Grand Partition Function in Defect Statistics
Authors: Landsberg P. T. , Canagaratna S. G.
Published: July 2007

It is explained how the grand partition function method can be used to discuss a) simple defects statistics in which one transition takes place; b) defect statistics in which two transitions take place (Frenkel or Schottky defects); c) more complex statistics. The latter is illustrated by a treatment of a mixture of Schottky and Frenkel defects, not previously discussed in generality.
Dislocations in AIIBVI and AIIIBV Piezoelectric Crystals
Authors: Smirnova I. S.
Published: July 2007

The problem is considered of the distribution of fields produced by dislocations in piezocrystals. The behaviour of the fields is analyzed for all possible dislocations available in b.c.c. crystals (in particular, with the sphalerite lattice) and in crystals with wurtzite lattice (existence of the radial and tangential component E; initiation of polarization vortexes). A considerable reduction in the symmetry of elastic stress fields is revealed for mixed dislocations in b.c.c. crystals.
Extended X‐Ray Absorption Fine Structure in RAl2Ga2 Intermetallies
Authors: Hatwar T. K. , Padalia B. D. , Ghatikar M. N. , Chopra D. R.
Published: July 2007

The near‐edge structure (NES) and the extended X‐ray absorption fine structure (EXAFS) associated with the K‐absorption edge of Ga and L3‐edges of the rare earths (R) (where R  La, Ce, Pr, Nd, Eu, and Yb) are studied in RAl2Ga2 intermetallics using a 600 mm curved crystal spectrograph. The results obtained are discussed in the light of the recent point scattering theory of EXAFS proposed by Lytle, Sayers, and Stern. The EXAFS data are used to obtain the nearneighbour distances in these newly synthesized compounds.
Le spectre de RPE de l'ion Mn2+ dans le tartrate de cadmium (CdC4H4O6 · 5 H2O)
Authors: Korkmaz M. , Aktaş B. , Dupont M.
Published: July 2007

Nous avons étudié, à température ambiante, le spectre de RPE de l'ion Mn2+ dans un monocristal de CdC4H4O6 · 5 H2O préparé par diffusion. L'ion Mn2+ entre dans le réseau cristallin comme substituant de Cd2+. Les sites de l'ion “impureté” ne sont pas équivalents vis à vis de la symétrie, mais sont magnétiquement équivalents.
Electrical Resistivity of Amorphous SnMn
Authors: Korn D.
Published: July 2007

Amorphous alloys of SnMn are produced by quench condensation from the vapour phase onto a substrate held at 5 K. The Mn concentration of the alloys varies between 5 and 60 at%. The electrical resistivity is measured in situ in the temperature range 1.8 to 390 K. The electrical resistivity of all amorphous SnMn alloys increases with decreasing temperature without approaching a constant value at low temperature. To explain the almost constant negative temperature coefficient the assumption is made that in amorphous Sn the orbital angular momenta of the p‐electron interact via spin‐orbit coupling with the Mn ion spin.
Cohesive Properties of Ge, Si, and Diamond Calculated with Minimum Basis Sets
Authors: Holland B. , Greenside H. S. , Schlüter M.
Published: July 2007

Ab initio calculations are presented of the cohesive properties of Ge, Si, and diamond. Electron‐electron interactions are treated within the local density functional approximation and electronion interactions are described by norm‐conserving pseudopotentials. The wave functions are expanded in local Gaussian orbitals. Acceptable results for equilibrium lattice constant, bulk modulus, and cohesive energy are obtained with few (eight to twelve) Gaussian functions per atom. The results, which are comparable to converged plane wave or local orbital calculations suggest the feasibility of studies of cohesive properties of systems with large numbers of atoms.
The Role of Surface Dislocations in the Continuum Theory of Lattice Defects
Authors: Marcinkowski M. J.
Published: July 2007

The close relationship between the concept of surface dislocations and the continuum theory of lattice defects is clearly demonstrated. In fact, it is shown that without the incorporation of surface dislocations into the classical continuum theories, it is not possible to obtain a complete and self‐consistent understanding of elasto‐plastic bending, grain boundary structure, and the behavior of deformed finite bodies in general.
Decay Kinetics and Polarization of the Ax Emission of KI:In Crystal
Authors: Nagirnyi V. , Soovik T. , Zazubovich S.
Published: July 2007

The decay kinetics and polarization of the AX emission are investigated for In centres in KI:In at 0.35 to 80 K. The parameters of the relaxed AX state are determined. Good agreement is obtained between the experimental results and theory, which suggests a strong interaction of impurity optical electrons with non‐totally symmetric vibrations of the crystal lattice.
Ideal Vacancy States in Si. A Study of the Empirical Tight‐Binding Method
Authors: Tuncay C. , Tomak M.
Published: July 2007

A series of calculations is performed to determine the sensitivity of ideal vacancy‐induced deep levels on the empirical tight‐binding parameters. A new parameter set is proposed for Si which yields a somewhat better band structure. The vacancy‐induced bound states and resonances are found to depend on the parameters rather sensitively while the band structures do not show this sensitivity.
The Thermoelectric Power of p‐Ge at Low Temperatures
Authors: Kaden E. , Günter H.‐L.
Published: July 2007

The thermoelectric power of lightly doped p‐Ge is measured in the temperature range of 5 to 300 K for the investigation of phonon scattering. The application of a simple theoretical model requires some knowledge of the dominant carrier scattering processes obtained by measurements of electrical conductivity and Hall effect. In terms of that model, the temperature dependence of the phonon drag part of the thermoelectric power can be attributed to only two phonon scattering processes: phonon‐phonon scattering at higher temperatures and phonon‐boundary scattering at lower temperatures. The constant phonon relaxation time of boundary scattering and its dependence on sample diameter has been observed at temperatures below 10 K.
Thermal Energy and the Equation of State for Alkali Halide Crystals
Authors: Bhende W. N. , Bakhshi P. S. , Shanker J.
Published: July 2007

The effect is investigated of recently calculated van der Waals potentials and new ultrasonic elastic data on thermal energy, crystal binding energy, and compressibility of alkali halide crystals within the framework of Hildebrand and Mie‐Grüneisen equations of state. Recent experimental data on the compression of LiF crystal are compared with the results calculated in the present work. It is found that the Hildebrand equation of state using an exponential form alongwith the vdW interactions yields better agreement with experimental data than those obtained from other potential models based on an inverse power form or the Mie‐Grüneisen equation of state.
Self‐Consistent Field Approximation for the Vibrational Spectra of Quaternary Alloys
Authors: Kleinert P.
Published: July 2007

A mean‐field approach is applied to the lattice dynamics of quaternary alloys. Specific results are obtained for the quaternaries AlxGa1−xAs1−yPy and GaxIn1−xP1−yAsy. Calculations are restricted to a mass‐disordered linear chain model. For the end‐member components the approach reproduces the results of the coherent‐potential approximation (CPA). The cluster density of states of eight atoms embedded in the mean‐field effective medium is compared with the numerical spectrum obtained for a 20000‐atom random chain by using the negative eigenvalue theorem. The predictions of the calculated mean‐field dielectric susceptibility agree at least qualitatively with experimental results. With some qualifications the approach can explain the change of mode behaviour within the composition range, as it is expected to occur in some III–V quaternary alloys.
Electric Field‐Induced First Order Raman Scattering in Alkali Halides
Authors: Dick B. G.
Published: July 2007

A shell model calculation suggests that, for electric fields of 2.5 × 105 V/cm, field‐induced first order Raman scattering cross‐sections may be only about two to three orders of magnitude smaller than those for second order Raman scattering.
Triplet Excitons in Non‐Resonant Molecular Pairs. Saturation Effects in Electron Spin Resonance
Authors: Reineker P. , Köhler J. , Schmid U.
Published: July 2007

For triplet excitons in non‐resonant pairs of differently oriented molecules the saturation of the ESR lineshape is investigated. The model takes into account the coherent exciton motion, an inhomogeneous distribution of electronic excitation energies, Zeeman and fine‐structure terms, and the microscopic interaction with phonons.
Tunneling from Deep Levels of l–c Type in Electric Fields
Authors: Köster H. , Kurnosova O. V. , Yassievich I. N.
Published: July 2007

The tunneling probabilities from deep levels of l–c type to the conduction band (for electrons) and to the valence band (for holes) of semiconductors are derived. In connection with these results an expression is calculated for the valence‐to‐conduction‐band tunneling current via deep levels in the forbidden band. Moreover it is shown that the effective tunneling energy differs from the real defect energy within the gap. This defect energy correction has direct consequences for the analysis of corresponding experimental investigations.
Structure and Bonding in Cubic IV–VI Crystals. IV. Evidence for Covalent Bonding in the IV–VI Family from the Extended Mulliken Scheme
Authors: Enders P.
Published: July 2007

The investigation of IV–VI compounds within the framework of the Mulliken scheme for atomic electronegativities extended recently by Watson et al. gives support for a predominantly covalent bonding character in these materials from atomic properties, too. Here, mono‐ and dichalcogenides and ‐oxides as well as solid solutions are considered.
The Rǒle of Two‐Level Systems in Amorphous Metallic Alloys. II. Micromagnetic Theory of Magnetic After‐Effects in Amorphous Ferromagnets
Authors: Kronmüller H.
Published: July 2007

The magnetic after‐effect in amorphous alloys is attributed to the reorientation of mobile atom pairs in regions of reduced mass density. It is shown that the model of two‐level systems (TLSs) gives an appropriate description of the thermodynamic and micromagnetic properties of the magnetic after‐effects. “Reversible” and “irreversible” relaxation processes are attributed to the annealing of mobile atom pairs and to changes of the energy splitting parameters of the TLSs.
Electronic Energy Bands of Pr under Pressure
Authors: De S. , Bose I. , Chatterjee S.
Published: July 2007

Praseodymium has a number of interesting phase transitions under pressure. Band structure calculations are performed for Pr in both, the low and high pressure region using the composite wave variational version of the APW method. Based on the results obtained, some conjecture is made to the nature of the most prominent transition.
Screening of the Spin–Orbit Exciton by the Electron–Hole Liquid in Germanium
Authors: Asnin V. M. , Stepanov V. I. , Zimmermann R. , Rösler M.
Published: July 2007

Absorption and modulated transmission in the spectral region of spin‐orbit transitions in Ge are measured and compared with calculations which take into account excitonic effects and their changes under high excitation. Measurements at high magnetic fields corroborate the findings.
Dissociation‐Accompanied Raman Scattering by Davydov Solitons
Authors: Eremko A. A. , Gaididei Yu. B. , Vakhnenko A. A.
Published: July 2007

A theoretical study is made of the Raman scattering by a molecular chain in the state of the soliton excitation accompanied by a soliton dissociation. The differential cross‐section of such a scattering is calculated.
Magnon Drops in One‐Dimensional Ferromagnetic Structures
Authors: Mirjanić D. Lj. , Bundalo Z. , Tošić B. S. , Šetrajčić J. P.
Published: July 2007

The spectrum of elementary excitations arising in processes of desintegration of magnon drops in one‐dimensional ferromagnetic structures is investigated. A new method of solving the gap equation is used. It is shown that those elementary excitations are gapless. This result is in accordance with Goldstone's theorem. It was also shown that these elementary excitations do not lead to the superfluidity effect.
Observation of FMR Surface Spin Wave Mode in Bulk Amorphous Ferromagnets
Authors: Frait Z. , Fraitová D. , Zárusová N.
Published: July 2007

A secondary mode is observed (at RT) in the FMR spectra of the bulk amorphous alloy Fe40Ni40B20 subjected to an anneal at 250°C. This mode is interpreted as the surface spin wave mode because the observed magnetic resonance field dependences on the microwave frequency and on the direction of the external field towards the sample surface agree with the conclusions of the macroscopic FMR surface‐mode theory.
Symmetry Groups of Cyclic Systems in Crystals
Authors: Evarestov R. A. , Leko A. V. , Smirnov V. P.
Published: July 2007

The symmetry group of a cyclic system in a crystal is defined. Its relation to the space group of an infinite crystal is cleared up. It is shown that all the irreducible representations of the cyclic system symmetry group can be found from the definite representations of the space group. The connection between Herring's and reduction group methods developed in the space group representation theory and the large unit cell method is established. A simple and efficient method of the symmetry‐adapted atomic orbitals generation is proposed and illustrated by the examples for α‐quartz and β‐cristobalite crystals (space group D63 and O7h).
Thermodynamic Properties of Liquid Hydrogen Metal
Authors: Ebeling W. , Richert W.
Published: July 2007

On the basis of earlier found Padé‐approximations for the free energy and the chemical potential of a fully ionized hydrogen system the transition from the atomic to the metallic state is discussed. Partial ionisation is studied by using the mass action law. The second critical point for hydrogen is found to be Tc = 16500 K and Pc = 22.5 GPa. An updated phase diagram of the transition region is presented.
Critical Temperature of a Quasi‐One‐Dimensional Ising Model. The Bethe‐Peierls Approximation
Authors: Yurishchev M. A.
Published: July 2007

The critical temperature of a three‐dimensional spatially anisotropic Ising model is computed by the Bethe‐Peierls method applied to the five‐chain cluster. A comparison is made between the results obtained and calculations based on other approaches.
Far Infrared Absorption by Hot Holes in p‐Ge under E ⟂ B Fields
Authors: Pozhela Yu. K. , Starikov E. V. , Shiktorov P. N.
Published: July 2007

A quantum mechanical approach and simulation of the hole energy distribution by Monte Carlo technique are used to calculate the field and wavelength dependences of the absorption crosssections of far infrared (λ = (40 to 500) μm) radiation by free holes interacting with phonons and impurity ions (σp) and due to the hole direct optical transitions between the light‐ and heavy‐hole subbands (σ12) for p‐type Ge in crossed electric and magnetic fields. The IR absorption by light‐and heavy‐holes emitting optical phonons is shown to increase sharply with E and dominate under strong heating. The absorption by holes interacting with impurity ions is shown to decrease significantly as the hole heating increases. This contribution can become negative. Under the population inversion of isomomentum states the amplification of the far IR radiation is shown possible only in the wavelength range λ = (40 to 200) μm. The necessary conditions are considered.
On the Theory of the Electron–Phonon Scattering Rate Including the Intra‐Collisional Field Effect
Authors: Ziep O. , Keiper R.
Published: July 2007

A transport equation for ballistic charge carriers which contains the influence of strong and spatially inhomogeneous electric fields in the collision integral is derived by use of Airy functions. A simple analytical expression for the scattering rate due to electron–phonon interaction is obtained including the intra‐collisional field effect. Near the threshold energies for several electron–phonon interaction mechanisms strong modifications of the corresponding scattering rates are calculated whereas the field‐induced change of the scattering rate is negligible for high‐energetic carriers.
Temperature Dependence of the Liquid Tin Resistivity
Authors: Gasser J. G. , Bretonnet J. L. , Bruson A.
Published: July 2007

The temperature dependence law of the liquid metal resistivity is usually attributed to that of the atomic structure. In the framework of the Percus‐Yevick approximation applied to hard spheres, various laws of temperature dependence of their diameter are used. They are deduced from different physical or thermodynamical properties (self‐diffusion, structure, entropy, isothermal compressibility) or by minimizing the free energy. A comparison with experimental measurements on liquid tin up to 1300 °C leads to a fairly good agreement.
Transverse Phonon–Helicon Interactions in Semiconducting Plasmas
Authors: Ghosh S. , Pathak M. S.
Published: July 2007

The transverse phonon‐helicon interactions in semiconducting plasmas having piezoelectric or deformation potential coupling or both (viz., n‐InSb) are investigated when the waves propagating along z‐axis are subjected to a magnetostatic field B0 in z‐direction and the electrons are drifted with a velocity v0 also along the z‐axis. Using the hydrodynamic model of plasmas, the dispersion relation D(Ω, k) is derived. The conditions for excitation and the gain per radian of the acoustohelicon waves are studied in detail under slow wave approximation. The analysis takes into account hot carrier effects and the temperature dependence of the momentum collision frequency. The dependence of gain per radian on the system parameters is investigated. It is found that the heating of the carrier decreases the gain.
Phase Diagrams of Ferromagnets with Cubic Single‐Ion Anisotropy
Authors: Domański Z. , Sznajd J.
Published: July 2007

The phase diagrams of S = 2 and 5/2 ferromagnets described by an Hamiltonian with a cubic single‐ion anisotropy term are discussed. It is shown that in the case of S = 2 the sixth‐order terms in the LGW Hamiltonian do not change the qualitative picture of the phase diagram, recently presented, only shifting the tricritical points. On the basis of the RG results it is found that for S = 5/2 the phase transition to the state with magnetization along [111] direction ought to be continuous whereas that to the state [001] is a discontinuous one.
Soliton Excitations in Alternating Antiferromagnetic Linear Chains
Authors: Sy H. K.
Published: July 2007

Linear chains of one half spins with anisotropic Heisenberg antiferromagnetic exchange are studied. Within the Hartree‐Fock approximation, such systems are shown to exhibit a spin‐Peierls transition. It is demonstrated here that the spin‐Peierls condensate also allows kink‐like soliton excitations, in analogy with the electron‐Peierls system. These spin‐solitons contribute to the magnetic susceptibility of the spin systems at low temperatures.
Magneto‐Reflectance of the B‐Exciton of CdS
Authors: Rosenzweig M.
Published: July 2007

The magneto‐reflectance of the B‐exciton of CdS is studied for fields up to 9.0 T. The spectra show a strong anisotropy of the Zeeman‐effect for H ⟂ c; the splitting is proportional to the sum of the g‐values of the valence and the conduction band for H parallel to the wave vector of incident light, but it is proportional to the difference of g‐values for H perpendicular to the wave vector. For the first time a change of the spectra with magnetic field inversion (pole‐changing effect) is observed; it appears for oblique incidence of light and results from the k‐linear term of the valence band. The spectra are discussed by lineshape analysis along the lines of excitonic polaritons. From the excellent agreement between experiments and calculations some new parameters of the B‐exciton can be determined: the g‐value of the B‐valence band g = 0.8 ± 0.1, the diamagnetic shift δdia = (2.0 ± 0.3) μe V/T2, and the different parts of the exchange interaction energy ΔLT = (1.4 ± 0.03) meV, Δ25 = (0.1 ± 0.05) meV and Δ21 = (0.15 ± 0.05) meV.
Excitons in Multi‐Layer Systems
Authors: Fomin V. M. , Pokatilov E. P.
Published: July 2007

Potential theory Green functions for multi‐layer systems with anisotropic dielectric permeability are found. The effect of boundary conditions on the potential and exciton energy properties is studied. In three‐layer systems the decrease in thickness of dielectric layers with electrode‐covered outer surfaces results in the decrease of the absolute value of exciton ground state energy. In fivelayer systems the decrease in thickness of dielectric layers which are bounded by vacuum causes an increase of the absolute value of exciton ground state energy.
The Contribution of Davydov Solitons to the Value of the Kinetic Coefficient of Electron Transfer along a One‐Dimensional Molecular Chain
Authors: Ivić Z. , Satarić M. , Žakula R.
Published: July 2007

An expression is derived for the kinetic coefficient of the electron transfer from donor molecules (Dm) to acceptor molecules (Al) along a quasi‐one‐dimensional molecular chain, to which Dm and Al are statistically attached. Using the method of the non‐equilibrium statistical mechanics and coherent states representation, the influence is studied of the transfer mechanism of Davydov solitons on the value of the kinetic coefficient.
Radiative Decay from Free and Bound Excitons in GaSe
Authors: Capozzi V. , Caneppele S. , Montagna M. , Lévy F.
Published: July 2007

Spontaneous excitonic luminescence in GaSe is investigated from 80 to 300 K and at weak laser excitation intensity. Radiative recombinations of direct and indirect free excitons are clearly observed. The analysis of the emission lines as a function of the temperature, of the excitation intensity, and of laser energy permits to attribute two lines of the intrinsic luminecsence to the recombination of direct and indirect excitons bound to defect centres localized in the energy gap. On the basis of recent theories on exciton‐impurity complexes, it is found that in the crystals the excitonic binding centres are deep neutral acceptors. From the dissociation energy of the bound excitons the ionization energy of the acceptor levels is estimated. Moreover, the measurements seem to indicate that thermal equilibrium between direct and indirect excitonic states is lacking below about 100 K.
Bound Exciton, Free‐To‐Bound and Electron‐Hole Plasma Luminescence in GaxIn1−xP (0.54 ≦ x ≦ 0.76)
Authors: Sotomayor‐Torres C. M. , Lumb M. D. , Walker G.
Published: July 2007

The luminescence of GaxIn1−xP (0.54 ≦ x ≦ 0.76) at 4.2 K is investigated. At high excitation intensities an electron‐hole plasma is observed in the sample with composition x = 0.54 and possibly in that with x = 0.74. No signs of an electron‐hole liquid are found in any of the samples studied. At low excitation intensities the luminescence spectrum is dominated by bound exciton transitions for samples with x = 0.76, 0.74, and 0.54 and by donor‐acceptor pair emission. For the sample with near crossover composition the spectrum is dominated by free‐to‐bound transitions. The results are discussed considering alloy disorder and are compared to those obtained in GaAs1−xPx and Ga1−xAlxAs under high excitation.
Optical and Electrical Properties of of Ruthenium‐Doped TiO2
Authors: Triggs P. , Lévy F.
Published: July 2007

Optical absorption spectra and electrical resistivity measurements are given of ruthenium‐doped TiO2. The effect on the system of doping with shallow donors (Ta, Nb) and of reducing in vacuum and in hydrogen is investigated. The results are discussed in view of recent EPR, Mössbauer, and thermogravimetric measurements. Fully oxidised Ru‐doped TiO2 shows an absorption band which is attributed to acceptor transitions of the Ru4+ ion. Absorption bands are observed in reduced and donor‐doped TiO2 which can be assigned to donor transitions of Ru3+ and Ru2+ ions. It is deduced that both treatments lead to reduction of Ru4+ to Ru3+ and Ru2+ before the appearance of free carriers, although differences exist between the effect of doping, of reducing in vacuum, and of reducing in hydrogen. An energy level scheme for the different valence states of Ru in TiO2 is proposed.
Dynamics of Paraelectric and Ferroelectric SbSI
Authors: Rao K. R. , Chaplot S. L.
Published: July 2007

The lattice dynamics of paraelectric and ferroelectric phases of SbSI is studied using a realistic interatomic force model comprising Coulombic and short range interactions, with covalency included between SbS pairs. Characteristic of highly anisotropic systems, the transverse acoustic modes along 〈100〉 and 〈001〉 directions exhibit anisotropy with respect to the TA modes along 〈010〉. This feature explains the nature of diffuse scattering seen earlier in X‐ray measurements. Comparison of optical data made with the results of this study indicates that experimental phonon frequencies and the LO–TO splittings are in reasonable agreement with calculated results. One can refine the calculations by suitable choice of covalent potential parameters and least‐squares‐fitting procedure; however, this has to await further optical and neutron experimental work.
Low‐Frequency Light Scattering in Superionic Glasses (AgI)x (Ag2O1B2O3)1−x
Authors: Fontana A. , Mariotto G. , Rocca F.
Published: July 2007

Light scattering measurements are made on superionic glasses (AgI)x(Ag2OnB2O3) 1−x from 2 to 400 cm−1 and in the temperature range 80 to 400 K. The data show the existence of a strong low frequency scattering which has a Lorentzian shape centered at zero frequency. A model is adopted from disordered crystals which treats such scattering as being due to the jumping of Ag ions. The fitting parameters are related to the probability of jump of the diffusing particles in various sites. An order of magnitude calculation relates the quantities obtained by the model with the completely independent measurements of conductivity and tracer diffusion; satisfactory agreement is found.
A MREI Model for Zincblence‐Like Phonons in CdGa2(SxSe1−x)4 Mixed Crystals
Authors: Parisini A. , Lottici P. P.
Published: July 2007

Results are given of the Raman scattering measurements on the composition dependence of the optical phonon frequencies in the pseudoternary defect chalcopyrite mixed crystals CdGa2(SxSe1−x)4 over all the composition range. The mode behaviour of all Raman features is tracked and a MREI (modified random element isodisplacement) model to reproduce the concentration dependence of the highest frequency polar zincblende‐like modes is presented.