bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Acoustic Phonon Disturbances on the Conductivity of Piezo‐Electric Semiconductors
Authors: Kocevar P. , Fitz E.
Published: July 2007

A closed expression is given for mutual electron‐phonon drag and heating corrections to the steady‐state mobility of weakly drifting non‐degenerate carriers in a polar extrinsic semiconductor of standard band structure with dominant piezo‐electric, acoustic deformation potential, and ionized impurity scattering. The approximations involved are discussed and their range of validity is explicitly stated in terms of electron‐phonon coupling constants, non‐electronic phonon relaxation times, carrier concentration, and lattice temperature. A detailed analysis of n‐GaAs yields corrections of up to 15% to the ohmic conductivity for moderate doping and for lattice temperatures around 20 K. Corrections of more than 20% can only be expected for the non‐ohmic (hotelectron) regime and lattice temperatures below 20 K.
Paramagnetic Resonance and Thermoluminescence of the PbWO4/PbMoO4 Mixed Crystal System
Authors: Hofstaetter A. , Oeder R. , Scharmann A. , Schwabe D. , Vitt B.
Published: July 2007

After X‐ray excitation of PbWO4/PbMoO4 mixed single crystals at liquid nitrogen temperature two types of MoO ‐electron centres are observed by means of EPR. For low molybdenum concentration axial S4‐symmetry centres are present, whereas in the case of crystals with high molybdenum content the centres undergo a small non‐axial symmetry distortion. The thermal decay of the MoO ‐centres, which contributes to the thermoluminescence emission of the crystals, is discussed with respect to its concentration dependence.
Comparison of Additional Boundary Conditions Based on Thermoreflectance Spectra of the An=1‐Exciton in CdS Crystals at Oblique Incidence
Authors: Stössel W. , Wagner H. J.
Published: July 2007

Thermoreflectance spectra of the An=1‐exciton in CdS are measured at 8 K for angles of incidence of the light ranging from 5° to 85°, using three different spatial arrangements between the c‐axis, the E‐ and k‐vector of light. Additional boundary conditions of Pekar, Ting et al. and Agarwal et al. are discussed for the first time in terms of optical constants. The refractive indices for these additional boundary conditions are derived, considering special features of CdS, such as optical anisotropy, exciton symmetry, and effective exciton mass anisotropy. Fitting calculations based on the experimental data show that Pekar's additional boundary condition gives the best agreement between theory and experiment.
Stress Dependence of Shallow Acceptor States in Semiconductors with Zincblende Symmetry
Authors: Pertzsch B. , Rössler U.
Published: July 2007

The spherical model for shallow acceptor states in cubic semiconductors is extended to consider the effect of uniaxial stress. The effective‐mass Hamiltonian including stress dependent terms is formulated using spherical tensor operators and dealt with by a variational procedure. By comparing the theoretical results with the donor‐acceptor recombination energy in stressed GaAs: Ge it is shown, that the stress dependence of the shallow acceptor is almost completely determined by the intrinsic properties of the host crystal, which are defined by the effective masses, the band deformation potentials, the spin–orbit splitting, and the dielectric constant.
Electrical Conductivity of Disordered Alloys with Strong Hybridization
Authors: Elk K. , Richter J. , Christoph V.
Published: July 2007

The influence of a strong hybridization on the electrical conductivity σ of disordered substitutional alloys is considered. A remarkable temperature dependence of the conductivity can already arise due to the temperature dependence of the chemical potential and the Fermi distribution function. The temperature coefficient of the conductivity can have both signs in dependence on the band filling. For special values of the electron concentration the temperature dependence of σ may be fairly large and comparable with that one obtained by the electron‐phonon scattering.
Hall Coefficient of Dilute Aluminium Alloys II. Application
Authors: Sato H. , Babauchi T. , Yonemitsu K.
Published: July 2007

The Hall coefficient of Al‐Ag, Al–Ga, and Al–Ge dilute alloys is measured at 4.2, 77, and 293 K as function of the magnetic field strength and solute concentrations. The range of validity of the practical formula given in the preceding paper is investigated for the case of the low field Hall coefficient of dilute alloys at 77 and 293 K.
Energy–Angle Distribution of 14N and 20Ne Ions after Passage through Thin Carbon Foils
Authors: Ellmer K. , Sturm J.
Published: July 2007

Energy–angle distribution of 14 and 20Ne ions penetrating carbon foils with thicknesses from 1.4 to 5.8 μgcm−2 for tilt angles up to 5° are determined. The energy of the incident ions ranged from 19 to 63 ke V (1.34 ≦ ϵ ≦ 7.96). The results are compared with the new theory of Meyer et al. on the energy‐angle distribution of heavy particles penetrating solids. Agreement is found for the angular dependence of the most probable energy loss, wheres pronounced deviations occur for the energy halfwidths‐angular dependence. An attempt is made to explain this discrepancy.
On the Theory of Light Propagation through Disordered Solids. Scattering from Configurational Fluctuations
Authors: Enderlein R.
Published: July 2007

The propagation of light through disordered solids is studied from a general point of view. It is shown that the total scattered light consists of two parts corresponding to phase space fluctuations and configurational fluctuations of the electromagnetic field. A general microscopic expression for the differential cross‐section of scattering from configurational fluctuations is obtained. The theory is applied to a free electron gas with fluctuating density and a non‐interacting system of polarization oscillators with fluctuating resonance frequency.
Luminescence from rare‐gas‐doped solid neon
Authors: Schuberth E. , Creuzburg M.
Published: July 2007

The luminescence in the vacuum‐UV from bulk polycrystals of Ne doped with Ar, Kr, and Xe is investigated. The exciting X‐rays produce free Ne host excitons which relax to their luminescing states. The guest atoms in the Ne matrix are excited, both by the free and by the relaxed excitons. The luminescence of the rare gas dopant atoms consisted of bands whose number, energies, and relative intensities are found not to change with any experimental parameter, in contrast to previous results. These luminescence bands are qualitatively explained to be due to atoms in a perturbing surrounding. Already at concentrations as low as 10 ppm, dimer formation is indicated by efficient luminescence from diatomic dopant molecules. All other observed luminescence is due to small contaminations of the supply gas and is found to be mainly due to oxygen and nitrogen.
Interatomic potentials for alkali metals. A comparative study
Authors: van Heugten W. F. W. M. , De Hosson J. Th. M.
Published: July 2007

A comparative study of interatomic potentials for alkali metals is presented. Both, the interaction functions which are derived from phonon‐dispersion curves and Heine‐Abarenkov‐Shaw optimized model potentials are given. For comparison with experimental data some defect calculations are made to obtain the vacancy formation and migration energies in Li, Na, K, and Rb.
Electron beam excited free exciton luminescence of GaSe
Authors: Schwabe R. , Thuselt F. , Hänsel T. , Lévy F.
Published: July 2007

On the layered semiconductor GaSe low temperature cathodoluminescence experiments are performed. Both, the temperature dependence of the free exciton luminescence and kinetical considerations lead to the conclusion that the GaSe band structure causes a peculiar temperature dependence of the exciton band population. The latter is established as a balance between recombination, the formation of excitons from holes and direct or indirect electrons, as well as dissociation of excitons.
Ferromagnetic nickel: Self‐consistent calculation of energy bands
Authors: Marschall E. , Bross H.
Published: July 2007

Generalized Wannier functions defined for a complex of bands are used to fit reliably an MAPW band structure of paramagnetic nickel up to about 1.5 Ryd above the Fermi energy. By adding intra‐atomic Coulomb interaction according to Hubbard the Hamiltonian of the ferromagnetic state is constructed and is solved self‐consistently. The exchange splitting is found considerably k‐dependent. In addition, spin–orbit coupling is taken into account.
Residual electrical resistivity of alloys
Authors: Aubauer H. P.
Published: July 2007

A general expression is derived for the residual electrical resistivity for alloys with arbitrary gradients of the concentration and the degree of order. It is applied to disordered alloys, to spinodally decomposed ones as well as for two phase structures, taking care of the finiteness of the electron mean free path Λ. In the latter case maxima of the residual resistivity appear, if the precipitate size is of the order of magnitude of the electron mean free path Λ. This agrees well with a very critical experiment, in which one and the same microstructure is analysed with electrons of varying mean free path Λ.
The anomalous Stark shift of the ground state energy of a donor–acceptor pair in an electric field
Authors: Arepev Yu. D. , Oleinik V. P. , Salkov E. A. , Tolpygo K. B.
Published: July 2007

Photon energies emitted from donor–acceptor pairs (DAP) in semiconductors in an electric field are calculated using a variational procedure. The linear combinations of s‐ and p‐type hydrogen‐like functions are used as trial wave functions of the pair. The magnitude of the Stark shift of the DAP ground state energy as a function R (the distance between the donor and acceptor) and θ (the angle between R and electric field direction E) are obtained for different values of E and m/m (m electron effective mass, m the same for a hole). It is shown that at small values of R and cos θ < 0 (R < aB, aB Bohr radius) the Stark shift is positive due to the strong polarization of the electron and hole clouds in the electric field.
Electron–phonon interaction and phonon conductivity of the n‐type semiconductors Mg2Ge and Mg2Sn at low temperatures
Authors: Singh Mahiradhwaj
Published: July 2007

It is shown that the expressions obtained by Singh for the relaxation rates of the resonance scattering of phonons by donor electrons for n‐type zemiconductors in presence of internal static and dynamic strains in the crystal can account very well for phonon‐conductivity results for the n‐type semiconductors Mg2Ge and Mg2Sn at low temperatures.
Raman Study of the Mixed System [(NH4)1−xKx]2 CuCl4 · 2 H2O
Authors: Sahni V. C. , Bansal M. L.
Published: July 2007

A Raman scattering study in the mixed crystal system [(NH4)1−xKx]2 CuCl4 · 2 H2O is reported. It is found that this system has a strong Raman‐active B1g mode, which dominantly involves NH4/K translations and shows a two‐mode behaviour. This behaviour is examined on the basis of a variant of the REI model. Frequency variations with concentration, exhibited by other modes are also studied.
The phase diagram of a system with two order parameters. Mott transition and ferromagnetism
Authors: Litvinov V. I. , Baginskii V. M. , Mitrofanov A. A.
Published: July 2007

The phase diagram of the extended Caron‐Pratt model is constructed. Competing order parameters describe ferromagnetic and metal–insulator phase transitions. The possible phases, the incompatibility of the order parameters, and the existence of the tricritical point are determined.
Cross relaxation studies in the Cr3+‐doped magnetically dilute paramagnetic Al2O3–Fe2O3 system. II. Effect of temperature and external magnetic field
Authors: Srivastava J. K. , Dale B. W.
Published: July 2007

Mössbauer measurements carried out at 4.2 and 300 K in the undoped and Cr3+‐doped paramagnetic Al2O3–0.04 mol% 57Fe2O3 system indicate a temperature independence of Fe3+–Cr3+ cross relaxation process in the diamagnetic Al2O3 lattice. The measurements made in an external magnetic field Hext, of 30 kOe, applied perpendicular to the γ‐ray beam, show that even in the presence of large Hext, Cr3+ ions have appreciable effect on the shapes of Mössbauer spectra.
A macroscopic calculation of the specific heats of a vacancy
Authors: Varotsos P. A.
Published: July 2007

The constant pressure specific heat Δc, associated with the temperature variation of the formation enthalpy of a vacancy, is calculated from macroscopic properties of the solid. A similar calculation of the corresponding “constant volume” specific heat Δc shows that its absolute value is equal to a few tenths of k. The value of Δc is positive whereas that of Δc is negative, in agreement with recent considerations of Gilder and Lazarus.
Temperature anomalies of the magnetic hyperfine field for Sn in metallic ferromagnets and the thermal expansion of the crystal lattice
Authors: Delyagin N. N. , Krylov V. I. , Nesterov V. I.
Published: July 2007

Great temperature “anomalies” of the magnetic hyperfine fields H for Sn impurity atoms in Fe and Co can be completely or partially explained by the thermal expansion of the crystal lattice. Experimental data are interpreted with the help of a simple model which is based on the representation of H as a sum of partial contributions of the opposite sign with the inclusion of the results of measurements of the pressure dependence of H. The radial dependence of partial contributions into H can be examined on the basis of a joint analysis of the data on the temperature and pressure dependences of H. A brief consideration is given to other possible causes of temperature “anomalies” of the hyperfine field for nonmagnetic atoms in metallic ferromagnets.
Temperature dependence of the relaxation time of the holes in bismuth
Authors: Gollnest H.‐J. , Kuka G. , Braune W. , Herrmann R.
Published: July 2007

Cyclotron resonance experiments are described on Bi single crystals at 35 GHz. The temperature dependence of the linewidth of cyclotron resonance (CR) of the holes is discussed in detail on the basis of a lineshape analysis. At a temperature of about 5 K a peculiarity in the temperature dependence occurs which can be explained on the basis of hole scattering by phonons.
Binding energy, compressibility, interionic potential, and transition temperature of simple metals obtained by the pseudopotential method
Authors: Khanna K. N. , Sharma P. K.
Published: July 2007

A one‐parameter model pseudopotential is applied to the problem of binding energy, compressibility, interionic potential, and transition temperature of simple metals. The results agree well with the experimental values.
A model for TTF‐TCNQ conductivity
Authors: Benoit C. , Galtier M. , Montaner A.
Published: July 2007

The dc and optical conductivity of TTF‐TCNQ is described by a modd including a collective mode and small polaron hopping. The optical conductivity is expressed in terms of the one phonon density of state. Satisfactory agreement with far infrared reflectivity measurements is obtained.
Elementary excitations in ferrimagnetic and antiquadrupolar biquadratic systems (S = 3/2)
Authors: Blaszczak E. , Westwański B. , Skrobiś K.
Published: July 2007

The diagrammatic methods for the Racah and standard basis operators are applied to the case of two‐sublattice systems with biquadratic interactions and spin S = 3/2. The elementary excitations are calculated in the (1/z)° approximation (z is the number of spins interacting with any given spin) in three phases: antiquadrupolar, ferrimagnetic, and ferromagnetic. In the antiquadrupolar phase there are two doubly degenerate branches of magnons. The spectrum of quadrons coincides with that of magnons. Three branches of magnons and two branches of quadrons are obtained in the ferrimagnetic phase. In the ferromagnetic phase there is one branch of magnons and one of quadrons.
The isotropic limit in anisotropic dislocation theory Green's functions in a crystal containing a dislocation pile‐up
Authors: Solovev V. A. , Zolotarev S. N.
Published: July 2007

A simple method is developed which provides the transition from two‐dimensional anisotropic ekpressions of dislocation theory to isotropic ones. Anisotropic expressions are given for the stress and displacement fields near a dislocation pile‐up (martensite crystal, crack, twin, slip band) in the presence of a single dislocation or a line force lying parallel to the pile‐up. By use of the method presented here, the corresponding isotropic formulae are obtained. These expressions are the Green's functions of dislocation theory for crystals containing a pile‐up type of defect.
Second‐order self‐energy for the Anderson model analytical results
Authors: Zieliński J. , Kozarzewski B.
Published: July 2007

An approximate analytical expression for the second‐order‐self energy for the symmetric Anderson Hamiltonian is obtained. It is shown that the results become exact at high temperatures and are very reasonable for the whole range of temperature and energy. This causes that the method can be relatively easily used for higher order terms making the most competent discussion of the Anderson model to be possible.
On the validity of assuming symmetrical laue diffraction conditions in calculations of diffraction contrast
Authors: Sheinin S. S. , Jap B. K.
Published: July 2007

The form of the dynamical theory normally used in calculations of diffraction contrast is based on the assumption of symmetrical Laue diffraction conditions. The results of previous investigations have shown this assumption to be valid for angles between the surface normal and the Brillouin zone boundary of up to 70°. The results presented in this paper show that although this is true for strong‐beam diffraction conditions, the error involved in calculations based on the assumption of symmetrical Laue diffraction conditions increases significantly as the deviation from the Bragg condition of the strong beam increases. In weak‐beam diffraction conditions significant differences between the symmetrical and non‐symmetrical Laue cases are obtained for angles between the surface normal and the zone boundary as small as 30°. This is verified by calculations of both diffracted beam intensities and dislocation profiles.
Necessity of a phase convention for effective g‐factors and role of the g‐factors in the Knight shifts of PbTe
Authors: Leloup J. Y. , Sapoval B.
Published: July 2007

It is shown that the g‐factors which are commonly used to describe the effect of a magnetic field on an electron in a semiconductor are phase‐dependent quantities. This difficulty, which is related to the non‐tensorial nature of the g‐matrix, is fundamental in a Knight shift theory. To solve this problem a phase convention is introduced which allows to define a „standard representation”︁ between Bloch spinors. This representation yields a common language in which the g‐factors are unambiguously defined and permits to assign a physical meaning to the sign of g⟂. The importance of the sign of the g‐factors is examplified by the surprisingly large ratio of the Knight shifts of Pb207 and Te125 in lead telluride.
Photoconduction in single crystals of a pentamethinium cyanine dye
Authors: Hauschildt D. , Fuhs W. , Hesse H.‐J.
Published: July 2007

The photoconductivity of a pentamethinium cyanine dye is studied on different crystal faces for light polarized parallel and perpendicular to the pentamethinium chain. According to the spectral dependence the first step in the photoconduction process is the excitation of singlet excitons. Free carriers are generated in the volume of the crystals. The photocurrent is recombination limited. The photoconductivity is found to be insensitive to irradiation with high doses of high energetic ions.
Cluster approximation for the spectral density of mixed diatomic systems
Authors: Kleinert P.
Published: July 2007

The spectral density of a mixed diatomic linear chain is investigated using the truncated‐T‐matrix approximation of Berk et al. Only the mass disorder is taken into account. If above the maximum host crystal frequency an impurity band exists then there occur remarkable differences between the cluster and CPA spectrum. In this frequency region the cluster results show some fine structures, which are investigated in dependence on the concentration of the impurities and on a short range order parameter, respectively. A not very pronounced fine structure occurs also between the acoustic and optic band if gap modes exist.
Energy levels of A and B excitons in wurtzite‐type semiconductors with account of electron–hole exchange interaction effects
Authors: Flohrer J. , Jahne E. , Porsch M.
Published: July 2007

The effect of both the complexity of the two upper valence bands as well as the electron–hole exchange interaction on the exciton binding energies in wurtzite‐type semiconductors is studied. The energy level scheme and explicit expressions for the lowest exciton states of both A and B series are given. Using recent very accurate experimental data on exciton energies in CdS, the averaged B band hole mass is estimated to 1.6mo, and the position of the n = 1 B(Γ2) exciton level to about 0.2 meV below the transverse B(γ5) level. The longitudinal–transverse splitting of γ5 excitons is calculated from a microscopic approach in excellent agreement with experimental data taking into account an interband momentum matrix element P = 21 eV screened by a background dielectric constant ε' = 8. The exchange parameters introduced by Cho are determined for CdS to 3j0 ≈ 1 meV and 9j1 ≈ 2.1 meV.
Investigation of sulfur molecular paramagnetic centers in SrCl2
Authors: de Siebenthal J. M. , Bill H.
Published: July 2007

S and S centers in SrCl2 single crystals are observed. The underlying experimental investigation is carried out by EPR, Raman, and optical absorption spectroscopy. The S centers show dynamical features in their EPR spectra. The temperature dependence of these spectra is compared with the results of the Kubo line shape theory. This enables to identify the motion as a thermally activated reorientation of the center between two equivalent equilibrium positions.
Electromagnetic absorption in antiferromagnetic chromium
Authors: Cuden C. B. , Guedes J. , Malbouisson J. M.
Published: July 2007

The inconsistencies between the theoretical and experimental predictions of the electromagnetic absorption in chromium, magnesium, and potassium are discussed. For the case of chromium, the absorptive part of conductivity as a function of frequency and temperature is calculated for the photon absorption by one‐electron, one‐hole, and electron–hole pair excitations. It is shown that the unphysical divergence of the absorptive part of conductivity for the photon frequency equal to twice the antiferromagnetic energy gap, found by Fedders and Martin, is removed by taking properly into account the statistical coherence effects.
A model theory of ferroelectric and other structural phase transitions of first and second order
Authors: Albers J.
Published: July 2007

A model is presented in which the appearance of displacive phase transitions is explained by short‐range internal forces. Electrically charged or uncharged parts of the structure are squeezed out of symmetrical positions and thus lead to a symmetry‐lowering and to phase transitions of ferroelectric or pure structural types. A simple microscopic potential describes transitions of first and second order in good agreement with data of ferroelectric crystals. The Taylor series expansion of this potential allows the comparison with Devonshire's theory.
On the dielectric response of solids II. Local field effects in the phonon‐induced density change of a semiconductor
Authors: Schulze K.‐R.
Published: July 2007

It is examined in one important example how the recently developed approximations for the consideration of local‐field effects in solid‐state screening do work for semiconductor problems. While the perturbation‐theoretical formula for the dielectric matrix leads to a noticeable overestimation of the semiconductor screening, the proposed local‐density approximation results in an excellent agreement with „exact”︁ data from extensive calculations.
Anisotropic K absorption in gallium
Authors: Weber W. M.
Published: July 2007

For linearly polarized X‐rays, a marked orientation dependence of the extended K‐absorption fine structure of a single crystal of gallium is observed at 5 K. Spectra calculated from Kostarev's theory of K absorption of unpolarized and polarized X‐rays in single crystals are in good agreement with the experiment.
Scattering of phonons and ultrasonic attenuation by donors in doped diamond‐type semiconductors
Authors: Singh Mahiradhwaj
Published: July 2007

The relaxation rates for scattering of phonons by bound donor electrons in diamond‐type semiconductors whose conduction band minima are along [100] direction, are obtained in presence of internal static and dynamic strains and an external magnetic field. The coefficients of ultrasonic attenuation by bound donor electrons are also obtained for the above semiconductors in presence of strains and magnetic field. The expressions for electron–phonon relaxation rate are used in explaining the phonon conductivity results of P‐doped silicon at low temperatures. The present theory gives excellent agreement between theory and experiment.
Boundary conditions for polarization waves in spatially dispersive dielectrics
Authors: Stahl A.
Published: July 2007

Spatial dispersion in bounded media affords so called additional boundary conditions (ABC) in order to match polarization waves. A method is described how these ABC can be found in the framework of phenomenological transport theory. The procedure is illustrated by two examples: a phononlike system and an electronic exciton system. The result is that without additional assumptions the gradient condition ΔP = 0 comes out as the preferred boundary condition. The commonly used Pekar condition, P = 0, is attributed to the case where the dynamical properties are disturbed in a boundary layer.
On the theory of resonant secondary radiation of excitons strongly interacting with phonons
Authors: Hizhnyakov V. V. , Sherman A. V.
Published: July 2007

A theory of resonant secondary radiation of self‐trapped Frenkel excitons strongly interacting with phonons both in self‐trapped and band states is developed. The absorption and ordinary luminescence spectra of such excitons are shown to be close in form to those of the impurity centre. Formulae for partial spectra are found. The corrections taking account of the electronic excitation transfer from site to site cause the asymmetry of the absorption spectrum and the excitation profiles of partial spectra. The width and general form of the exciton band can be determined from the value and sign of the asymmetry.
Spin—lattice relaxation of 19F and magnetic couplings in rare‐earth fluorides
Authors: Svare I.
Published: July 2007

Measured relaxation times T1 and T1ρ of 19F in CeF3, PrF3, NdF3, and SmF3 from 100 to 400 K give information about electron magnetic moment correlation times. Exchange‐type couplings Ce3+F and Ce3+Ce3+ are larger than the corresponding dipolar couplings. Such couplings are less important in PrF3, and they do not influence T1 and T1ρ in NdF3 and SmF3. Raman electron spin—lattice relaxation ∼ T2 dominates over spin flips in SmF3, and direct relaxation ∼ T dominates in NdF3.
Theory of local electronic states in a semi‐infinite mixed crystal
Authors: Ueba H. , Ichimura S.
Published: July 2007

A theory is presented to study the local electronic states in a semi‐infinite mixed crystal, by extending the coherent potential approximation developed in the study of an infinite bulk crystal to a suitable one for a semi‐infinite crystal. The effect of semi‐infinity of a crystal is taken into account by Sugakov's method in which the wave function of an electron is expressed in terms of a standing wave with nodes. The site‐dependent coherent potentials are introduced to calculate the local density of states in a semi‐infinite mixed crystal. The appearance of the localized surface state is also discussed.
Vacancy and interstitial configuration in hexagonal close packed metals
Authors: Tomé C. N. , Monti A. M. , Savino E. J.
Published: July 2007

The lattice static Green function and computer simulation methods are used in order to calculate the lattice distortion owing to a vacancy and a self‐interstitial in a hexagonal close packed lattice. A semidiscrete method is developed for the perfect lattice Green function evaluation. An empirical potential deduced by fitting magnesium parameters, and a pseudopotential, deduced for that metal, by Appapillai and Heine, are adopted for the calculation. The validity of using those potentials is discussed. An almost isotropic and very small lattice distortion is calculated for the vacancy, while a large and anisotropic lattice distortion calculated for an interstitial atom determines the trigonal (tetrahedral) configuration to be stable with respect to the hexagonal (octahedral) one.
Intraband absorption in lead chalcogenide mixed crystals
Authors: Kurowska A.
Published: July 2007

Free carrier absorption due to the chemical disorder is calculated for lead chalcogenide mixed crystals, taking into account the actual band structure. It is found that in an alloy the absorption coefficient due to composition fluctuations may be comparable with the intraband absorption due to the LO polar scattering, at low temperatures.
Isomer shift and quadrupolar splitting of the Mössbauer spectrum of ferroelectrics
Authors: Bashkirov Sh. , Lebedev V. N.
Published: July 2007

The parameters of the Mössbauer spectrum of Fe3+ ions in ferroelectrics are considered. It is shown that the internal electric fields in ferroelectrics cause the strong polarization of the—covalency occupied 4s shell of Fe3+. This gives the significant contribution to the isomer shift and quadrupolar splitting of the Mössbauer spectrum. For BaTiO3, this contribution determines both sign and magnitude of the observed discontinuous change of the shift at Tc. It is also shown that the structure reconstruction of BaTiO3 decreases the isomer shift at the transition in the ferroelectric phase. The contribution of the electrically polarized 4s shell of Fe3+ ion to the quadrupolar splitting of the Mössbauer spectrum for BaTiO3 gives more than a half of the observed value of the quadrupolar splitting.
Correlation of zero‐field splittings and site distortions I. MnCl in approximately trigonal symmetry
Authors: Sachs H. , Lehmann G.
Published: July 2007

EPR parameters for Mn2+ in single crystals of (CH3NH2)2ZnCl4 and (enH2)2ZnCl6 (en = ethylene diamine) are reported. The axial splitting parameter B for these and two other systems from the literature are approximately proportional to the size of the trigonal site distortion. The rhombic parameter B also correlates well with the amount of deviation from true C3 symmetry. For large distortions the z‐axes of the EPR parameters are close to the direction of the longest ZnCl bond. Thus the distortion of the first coordination sphere of the paramagnetic ion appears to determine the size of the second order fine structure parameters if the bond lengths differ by at least 1 pm.
Spin wave stiffness constant of narrow‐band ferromagnetic alloys with random hopping
Authors: Kolley E. , Kolley W.
Published: July 2007

The spin wave stiffness constant D of ferromagnetic binary metallic alloys is derived at zero temperature from a random Hubbard model including diagonal and off‐diagonal disorder. The fluctuations of the hopping integrals are restricted to the additive limit. Vertex corrections to D due to the randoness of the transverse spin current are calculated in an extended CPA. D is renormalized by electron‐electron correlations within the coherent horizontal ladder approximation. Stability and damping of the spin waves, Ward relations, and the electrical conductivity are discussed.
Impurity scattering effect on the cyclotron resonance of carriers in Cu2O
Authors: Goltzené A. , Schwab C.
Published: July 2007

Cyclotron resonance is made on purest and deliberately Fe‐doped Cu2O to assess the extrinsic origin of one of the two polaron masses previously reported (0.58m0 and 0.69m0). Only one mass is observed, which shifts to higher values with doping and is excitation wavelength dependent, except for the best undoped material. The latter shows the lowest mass, ascribed therefore to the uppermost valence band. Material improvements are discussed with respect to the carrier lifetimes.
Certain features of semiconductor behaviour in strong parallel magnetic and electric fields I. Effect of electric field on the magnetic moment of a specimen
Authors: Berezhkovskii A. M. , Ovchinnikov A. A.
Published: July 2007

It is shown that the spin contribution to the magnetic moment of a semiconductor specimen placed in strong parallel magnetic and electric fields becomes zero when the energy of spin splitting in magnetic fields is a multiple of the energy difference between adjacent Wannier‐Stark levels in electric fields.
On the static conductivity of a heavily doped semiconductor
Authors: Arbuzov Yu. D. , Evdokimov V. M.
Published: July 2007

It is shown that the static conductivity of a heavily doped semiconductor may be obtained in terms of a transport relaxation time. Not only the term of Born's approximation is regained in the framework of the assumptions made but as well the terms associated with the scattering by two impurities are taken into account. The relevant correction to the static conductivity is calculated.
Eigenoscillations of Hot Electrons in an Inhomogeneous Semiconductor under Classically Strong Magnetic Field
Authors: Dykman I. M. , Prokhnitskii L. A.
Published: July 2007

An extrinsic semiconductor with periodic impurity distribution is studied. The distribution function in such a semiconductor applied to a mutually perpendicular heating electric field and a classically strong magnetic field is determined. The spectrum of electron gas eigenoscillations is calculated. The frequencies of eigenoscillations are proved to be considerably sensitive to the electric field strength. The spatial periodicity of the semiconductor changes the number of vibrational modes. Similarly to other works, semiconductor inhomogeneity results in resonance‐type dependencies for some modes. The magnetic field is also found to be the factor changing significantly the spectrum of eigenoscillations.
Some Special Models of the Spatial Theory of Dispersion
Authors: Litzman O. , Holý V.
Published: July 2007

A classical system of dipoles is investigated interacting via retarded dipole‐dipole and nonretarded “mechanical” forces. On the basis of formulae deduced in previous papers two models of mechanical forces (exponential model and next‐nearest neighbour model) are investigated. After evaluating of refraction indices and reflexivity for both the models it is shown that the results are comparable with those of the continuous model dielectric.
An Improved Molecular Field Approach to the Triangular Ising Antiferromagnet
Authors: Doman B. G. S.
Published: July 2007

The phase transitions are examined of a triangular lattice with Ising model interactions which are antiferromagnetic for nearest neighbours and ferromagnetic for second neighbours. It is assumed that the ferromagnetic interaction is much smaller than the nearest‐neighbour interaction. The average spin is worked out on a given site for all possible spin configurations of the neighbours. This is then weighted according to the neighbours' probabilities of being up or down. Several possible states of the system are found. The stable state is selected by using the free energy.
Fluorescence of Interstitial Atomic Hydrogen in Alkali Halides Doped with I−
Authors: Lohse F. , Spaeth J. M.
Published: July 2007

In KCl and RbCl doped with I− interstitial atomic hydrogen shows fluorescence emission if one of the four chlorine neighbours is replaced by an I−. In KCl one emission band at 2.84 eV with a radiative decay time of 14 ns and two overlapping bands at 1.97 eV with decay times of 34 ns and 720 ns (at 4 K) are observed. Similar results are found for RbCl. The results are interpreted as due to two charge transfer type relaxed excited states, one of which is a spin quartet and responsible for the long radiative lifetime.
On the Interaction between F‐ and α‐Centres in KBr
Authors: Bosi L. , Nimis M.
Published: July 2007

Luminescence measurements show an increase in the F‐centre lifetime in KBr, corresponding to a critical α‐centre concentration after F→F′ conversion. An inhibition of the luminescence quenching effect, related to the F‐centre density, is also observed. The results are discussed in respect of the Crandall photoconductivity data and explained on the basis of an interaction mechanism that involves the electron capture cross‐section by α‐centres and the mean distance between F‐centres.
Magnetopolaritons in Wurtzite‐Type Crystals
Authors: Röseler J. , Henneberger K.
Published: July 2007

The influence of a magnetic field on the polariton dispersion resulting from the An = 1 excitons in wurtzite‐type crystals is calculated by the diagonalization of the Hamiltonian describing magnetoexciton–photon interaction. Remarkable changes compared with the field‐free dispersion are obtained: Beside energy shifts, new branches and crossing points arise due to the field‐induced mixing of exciton states. The results should be interesting also with respect to final states of the radiative decay of biexcitons in crystals like CdS and CdSe.
Chemical Shifts of the L3‐Absorption Edge of Pt in the Rare Earth–Platinum Intermetallic Compounds
Authors: Koul P. N. , Hatwar T. K. , Ghatikar M. N. , Padalia B. D.
Published: July 2007

Chemical shifts of the L3‐absorption edges of Pt in RPt2 and RPt5 compounds are measured and correlated with the effective charges calculated using Siegbahn's method. It is found that the L3‐edge shifts towards the lower‐energy side of the Pt metal edge in RPt2 compounds, while in the case of RPt5 the shifts are in opposite direction. An attempt is made to explain the behviour of these chemical shifts.
OOn the Origin of Localized Magnetic States in Transition Metal Alloys II. Doubly Degenerate Orbitals
Authors: Oleś A. M. , Morkowski J.
Published: July 2007

A doubly degenerate model of transition metal impurities is solved in a hierarchy of approximations which conserve up to first four moments of the spectral density function. It is shown that the Hund's rule plays a crucial role in the local moment formation stabilizing configurations with more than one electron (hole) per impurity. The present model is qualitatively consistent with available experimental data and explains why magnetic moments are formed on Fe or Co atoms while they cannot be stabilized on Ni.
Theoretical Calculation of the Absorption Energy of the F‐Centre in Alkali Halides
Authors: Dochy F.
Published: July 2007

The absorption energy of the F‐centre in all 20 alkali halides are calculated in a pseudopotential theory developed by Bartram, Stoneham, and Gash, using a point‐ion lattice with an ion‐size correction. Polariztion and lattice distortion effects are included. Different anlaytical forms for the trial pseudo‐wave functions are investigated. It is found that the empirical reduction factor, introduced by Bartram, Stoneham, and Gash depends strongly on the type of wave function used.
The Electron Structure of 3d Metals
Authors: Ksendzov Ya. M.
Published: July 2007

The available data on the electron energy losses in 3d metals from Sc to Cu are analyzed, and the energy loss maxima corresponding to plasmons are isolated. The number of plasmons changes from one in the beginning of the 3d series to three starting with Fe. This implies that the 4s + 3d electrons can be hybridized in one band or distributed over two or three bands separated by gaps. Taking into account the field acting on the core electrons (the Ar shell) makes it possible to obtain a refined formula for the effective plasma frequencies, which is used to calculate the electron concentration in the conduction and valence bands of the 3d metals. A proper consideration of the conditions at which the electrons of the valence bands, similar to those of the conduction bands, can be regarded as a quantum plasma permits to construct a diagram of distribution for the electron and spin densities of states as a function of energy. The electron density distribution in the 3d metals differs from that for the 3d atoms as well as from the one calculated for metals in recent theoretical works. The diagram of the electron and spin densities of states thus obtained is compared with other experimental data, viz. the X‐ray and neutron form factors, Hall effect, optical, photoemission, and X‐ray emission spectra.
Stress‐Induced Alignment of Jahn‐Teller Centres Cr2+ in ZnSe Crystals. Optical Study
Authors: Ryskin A. I. , Vasilev A. V. , Natadze A. L.
Published: July 2007

Uniaxial compression of ZnSe–Cr crystals along the fourth‐order axis results in shift and splitting of the zero‐phonon lines of the absorption band, connected with the 5B̂2(5T2) → (5Â1 + 5B̂1) (5E) transition of the impurity Cr2+ ions, and in dichroism, which is caused by the reorientation of the Jahn‐Teller centres Cr2+ along the stress direction. Spectra of stressed crystals are calculated on the base of the exchange‐charge model. In imperfect (twinned) ZnSe crystals two types of Cr2+ centres are observed. These centres are identified as Cr2+ ions in the interlayers of a twin structure.
Reflections of a New Type in the Mössbauer Diffraction Pattern
Authors: Kolpakov A. V. , Ovchinnikova E. N. , Kuzmin R. N.
Published: July 2007

A new type of the Bragg reflections in the Mössbauer diffraction pattern, apart from the well‐known magnetic and quadrupole ones, is discussed. These reflections may be observed in the Mössbauer diffraction pattern only in the case when there are both the magnetic field and the electric field gradient at nuclei of Mössbauer isotope, i.e. two static internal fields with symmetries described by the ∞/m and ∞/mmm groups. The Mössbauer diffraction pattern of a KFeF4 single crystal is considered in detail.
One‐ and Two‐Phonon Raman Scattering in Ternary Phosphides ZnSiP2, ZnGeP2, CdSiP2
Authors: Gorban I. S. , Gorynya V. A. , Lugovoi V. I. , Krasnolob N. P. , Salivon G. I. , Tychina I. I.
Published: July 2007

One‐ and two‐phonon Raman scattering (RS) of orientated single crystals of ZnSiP2, ZnGeP2, and CdSiP2 are investigated. For the first time in ZnSiP2 the lattice vibrations B2(L/T) 146/145 and B1 466 cm−1 are observed, and the values of L–T splitting of polar modes are determined. It is concluded that in crystals of ZnGeP2, ZnSiP2, and CdSiP2 a completely symmetric component of the second‐order RS spectra is formed by overtones and gives the distribution of the phonon state density of the lattice of these compounds. This distribution is determined in the main by the points Λ, T, N of Brillouin zone and has the general form for all compounds investigated. An estimation is given of the frequencies ofinactive A2‐phonons in ZnGeP2, ZnSiP2, and CdSiP2.
Certain Features of Semiconductor Behaviour in Strong Parallel Magnetic and Electric Fields III. Interband Absorption
Authors: Berezhkovskii A. M. , Ovchinnikov A. A.
Published: July 2007

It is shown that under certain conditions the absorption spectrum of a semiconductor placed into strong parallel magnetic and electric fields transforms from a continuous into a discrete and equidistant form with energy intervals between the adjacent absorption maxima equal to the energy of a Wannier‐Stark ladder step.
Theory of Anisotropic Electron–Phonon Interaction in Copper I. Electron–Phonon Matrix Elements
Authors: Schmidt H. , Mann E.
Published: July 2007

The electron–phonon interaction in copper is calculated on the basis of realistic wave functions and taking into account all anisotropies of the system. The electron wave functions are derived from a combined interpolation scheme, in which the wave functions are assumed to be composed of both, plane waves and Bloch sums of atomic d‐functions. Because of the “pseudo” character of the wave functions thus obtained, these have to be combined with a pseudopotential in order to render the correct electron–phonon matrix elements; this contrasts with an earlier paper in the literature. Taking a slightly modified Cohen‐Heine pseudopotential and the plane‐wave contributions only, leads to a satisfactory agreement between calculated and observed anisotropic quantities. The other contributions to the matrix elements are critically discussed. Applications will be considered in a subsequent paper.
Infrared Reflection and Raman Scattering Studies of the Vibrational Properties and Structure of As2S3Gex Glasses
Authors: Giehler M. , Pilz W.
Published: July 2007

Infrared reflection and Raman spectra of As2S3Gex (0 ≦ x ≦ 35 at%) glasses are studied. The spectra are explained in terms of vibrational modes of atomic building blocks the investigated glasses are composed of. Particularly, the vibrational properties of the As2S3Gex (x < 4 at%) glasses are due to internal vibrations of AsS3/2 pyramidal and weakly As‐rich AsrSs (r/s ⪅ 1) building blocks. The number of GeS4/2 tetrahedral building blocks is very small, therefore, these structures do not noticeably affect the infrared reflection and Raman spectra of the considered glasses. The vibrational properties of the As2S3Gex. (4 ⪅ x ⪅ 14 at%) samples are dominantly affected by vibrations of As‐rich AsrSs (r/s ≈ 1), GeS4/2 tetrahedral, and AsS3/2 pyramidal building blocks. (The number of AsS3/2 pyramidal building blocks approaches zero in samples with Ge contents above about 10 at%.) Raman spectra indicate that samples with Ge contents between about 4 and 12.5 at% contain realgar‐like microcrystals. The vibrational properties of the As2S3Gex (x > 14 at%) glasses mainly are caused by vibrational modes of GeS4/2 tetrahedral and strongly As‐rich AsrSs (r/s ⪆ 1.3; including AsAs3/3) building blocks. Stretching vibrations of AsAs bonds of these strongly As‐rich AsrSs building blocks are indicated in the Raman spectra of the considered glasses. In glasses with x ⪆ 23 at% Ge content the number of AsS bonds becomes zero, therefore weakly Ge‐rich GeuSv (u/v ⪆ 0.67) building blocks are formed.
Spatial Dispersion Effects in the Transmission Spectra of Semiconductors in the Region of Exciton Resonances
Authors: Dietrich B. , Voigt J.
Published: July 2007

The influence of spatial dispersion on the transmittivity of a semiconductor platelet in the region of an exciton resonance is investigated theoretically. In detail the dependences on the exciton parameters such as translational mass, polarizability, and damping are discussed. It is found that all the peculiarities observed experimentally for the A ground state exciton in CdS can be explained quantitatively.
Unifying Concepts in the Theories of Elasticity, Plasticity, and Dislocations
Authors: Marcinkowski M. J.
Published: July 2007

For the first time, the basic underlying concepts linking the fields of elasticity, plasticity, and dislocation theory are formulated. The methods used are those of differential geometry and are illustrated by a number of very simple examples.
On the Homology of Lattice Vibrations of Rare‐Gas Solids
Authors: Ramamurthy V. , Rajendraprasad S. B.
Published: July 2007

Investigations of the dependence of phonon frequencies of rare‐gas solids on their interatomic distance, r, reveal that they satisfy an empirical relation, Mv2rα = δ(q), a constant which depends on q, with α = −2. 74 ± 0.14 at all wave vectors and he nce is homologous in the case of argon, krypton, and xenon. It is shown that the homology of lattice vibrations depends on the nature and strength of the interatomic forces, but not on the crystal structure of the solids. The influence of the zero‐point energy and the consequent differences in the behaviour of rare‐gas solids and alkali metals are discussed.