bluuebunny/crossref_metadata_2025 huggingface dataset:
Galvanomagnetic phenomena in semiconductors with non‐parabolic dispersion law at non‐elastic scattering of carriers
Authors: Tolpygo H. I.
Published: July 2007

By means of [1] the distribution function, conductivity, Hall coefficient, and magnetoresistance are calculated for non‐degenerate semiconductors with Kane's dispersion law in the temperature and concentration ranges where impurity and optical scattering dominate. Intrinsic conductivity and scattering of electrons by holes are considered at elevated temperatures. Numerical calculations are made and compared with experimental data for n‐InSb. A complicated temperature dependence of the Hall factor with a characteristic “dip” at kT ≈︁ ħωopt is obtained. Some discrepancy of the theoretically evaluated mobility with experimental results at high temperature is probably due to a not exact knowledge of the parameters of interaction with optical phonons and the neglect of the temperature dependence of the effective mass at the bottom of the conduction band.
Inter‐valence band magneto‐absorption in tellurium
Authors: Miura N. , Tanaka S.
Published: July 2007

The infrared magneto‐absorption of tellurium due to the inter‐valence band transition of holes was investigated between 1.7 and 4.2° K. Magnetic fields up to 44.9 kOe were applied in the directions of the three crystallographic axes. For H⊥c‐axis, an oscillatory absorption was observed, which is caused by the harmonic transition of holes from the lowest lying impurity state. The effective cyclotron mass of the split off band was estimated to be \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {m_z m \bot } = 0.11\;\,m_0 $\end{document}. The results were analysed using the dumb‐bell model of the valence bands involving the difference in the transverse effective masses between the two valence bands.
The elastic constants of cuprous oxide
Authors: Hallberg J. , Hanson R. C.
Published: July 2007

The elastic constants of cuprous oxide have been measured by a standard pulse echo technique. The low temperature limiting values of the stiffness moduli are (in units of 1011 dyn/cm2) C11 = 12.1 ± 0.5, C12 = 10.5 ± 0.4, C44 = 1.09 ± 0.03. The Debye temperature calculated from these is 181° K. Both shear moduli show an unusual increase with increasing temperature.
Structure, energy, and periodic potential of kinks in screw dislocations for B.C.C. lattices
Authors: Hartmann O. , Pegel B.
Published: July 2007

The widths, energies, and periodic potentials of kinks in undissociated screw dislocations are numerically computed within a modified Dietze and Leibfried model. The kinks considered are assumed to lie in a {110} plane. Results are presented for Nb, Mo, and Fe. The kink widths range between 0.8 and 2.6 lattice constants while the amplitudes of the periodic potential felt by the kink when moving along the dislocation are found to be 6, 15, and 2 meV for Nb, Mo, and Fe, respectively. The kinks are short and the kink widths differ, depending on the kink position, by about 100%. The kink energies range between 0.5 and 4 eV.
Energy loss and energy straggling of well channelled hydrogen, helium, and lithium ions in gold
Authors: Högberg G. , Nordén H. , Skoog R.
Published: July 2007

The stopping cross‐sections of well channelled H+, D+, He+, and Li+ ions have been determined in thin gold single crystals along the 〈110〉, 〈112〉, and 〈111〉 directions. The energy range studied was 2 to 54 keV. The energy straggling has been investigated as a function of energy loss for different mean energies, kinds of ions, and crystallographic directions. In some cases the energy loss spectrum showed a structure.
Nuclear magnetic relaxation and random reorientations in molecular crystals
Authors: Ivanov E. N.
Published: July 2007

A calculation is made of the half‐width of the nuclear magnetic resonance line Δω1/2 and the spin‐lattice relaxation time T1 in molecular crystals. It is suggested that the relaxation is due to the modulation of the intermolecular dipole–dipole interaction of random reorientations of molecules. The random reorientations of molecules in a crystal lattice are treated on the basis of the random rotational travelling model, earlier suggested by the author. Δω1/2 and T1 are found to be determined by the number of equilibrium reorientations of the molecule. For different elementary rotational angles (π/2, π/4, π/6) calculation formulae are given. The nature of random reorientations is discussed.
Energy transfer and rate equations—application to ruby
Authors: Heber J.
Published: July 2007

Atomistic rate equations are represented for the transfer of optical excitation energy between donor and acceptor ions in ionic crystals. The physical assumptions which are necessary to deduce the phenomenological collective rate equations from the atomistic ones are specified. Time resolved measurements of the energy transfer from isolated Cr3+ ions to Cr3+ pairs in ruby are discussed. It is shown that, contrary to the present ideas, the collective rate equations cannot be applied in this case.
Electron transitions through and over potential barriers in solids
Authors: Christov S. G.
Published: July 2007

Using the approach of Harrison, a general expression is derived which permits to calculate the probability of electron transitions through and over potential barriers in solids for any given energy value. The conditions at which this expression is valid are specified.
The optical properties of Sb2Se3Sb2Te3
Authors: Procarione W. , Wood C.
Published: July 2007

The optical properties of single crystal specimens of Sb2Te3Sb2Se3 solid solutions have been investigated in the photon energy range 0.04 eV to 6.5 eV. A wide range of solid solutions having hexagonal structure were found to exhibit properties closely corresponding to the isostructural compounds Bi2Te3 and Bi2Se3. Small indirect band gaps approaching semimetallic values were obtained. The high free‐carrier concentrations gave rise to plasma effects in the near infra‐red. In contrast Sb2Se3 is orthorhombic with a direct band gap near 1 eV. The chemical bonding concepts applied to similar systems seem applicable with only slight modification.
Charge Compensation by O2− Vacancies in Cr3+‐Doped SrTiO3
Authors: Meierling H. D.
Published: July 2007

ESR measurements of Cr3+ ions in SrTiO3 at orthorhombic lattice sites in the cubic phase of the crystal are described. The orthorhombic distortion is caused by an oxygen vacancy in the neighbourhood of the Cr3+ ion. A model of the displacement of the neighbouring oxygen ions is proposed. The values of the constants of the spin‐Hamiltonian are given.
The F Center in KCl Crystals Part II: Optical Properties and Analogy with the H Molecule
Authors: Aegerter M. A. , Lüty F.
Published: July 2007

F centers in KCl crystals were so far identified by one absorption band at 1.4 μm. Several new absorption bands found in the visible and near UV are studied at LHeT with an almost perfectly aligned system. Energy positions, dichroic behavior and oscillator strengths of these transitions are found in close agreement to the calculated states of the H molecule corrected with a single dielectric constant. Excitation of the lowest excited 2pσu state at 1.4 μm leads with a temperature independent quantum efficiency to the IR emission at 1.67 μm. The experimental band shapes of these IR transitions with their associated zero phonon line were analyzed using a simple model for the electron coupling. Low temperature excitation of all higher absorption states (2pπu, etc.) produces a 600 nm luminescence. At higher temperature a thermally activated process transfers the excitation energy to the lowest excited state (2pσu) quenching the 600 nm luminescence and producing the IR emission.
Energy Bands of Potassium Halides (Green's Function Method)
Authors: Overhof H.
Published: July 2007

The energy bands of KCl, KBr, and KI have been calculated using the relativistic Green's function (KKR) method. Besides the results of calculations with atomic potentials for KCl, KBr, and KI results for KI from ionic potentials with Kohn‐Sham and Slater exchange potentials are also compared. Special care is taken to interpret the excitonic structure of KI in terms of band separations. For this purpose extreme ultraviolet data are used to confirm the interpretation.
Optical Absorption Intensities of Ho3+ in YPO4
Authors: Becker P.‐J.
Published: July 2007

The intensities of the electric dipole transitions within the 4f10 configuration of Ho3+ in YPO4 have been measured. They can be described with the Judd‐Ofelt theory. The fitted parameters show that the configuration 4f10 interacts stronger with the configurations nd94f11 (n = 3, 4) than with the configurations 4f9nd (n ≥ 5). The total interactions with g‐electrons and with d‐electrons are of the same order.
Electron Microscope Image Contrast from Dislocation Loops
Authors: Bullough R. , Maher D. M. , Perrin R. C.
Published: July 2007

Experimental electron microscope images of dislocation loops in molybdenum have been compared to theoretical loop images displayed in the form of computer simulated micrographs. The exact displacement field around a circular edge dislocation loop has been calculated using isotropic elasticity theory; this displacement field together with the two‐beam dynamical theory of electron diffraction contrast have been used to compute image intensities. Specific results are given for loops of radius ≈ 250 Å and ≈ 25 Å. Their contrast has been studied over a narrow range of the numerous variables which are known to influence image features. It has been found that the general topographical character of certain prominent experimental images is qualitatively accounted for by the simple “elastic” defect model with the two‐beam theory of electron diffraction.
The Structure of the Indirect Absorption Edge of CdO
Authors: Kocka J. , Konak C.
Published: July 2007

The optical absorption in CdO single crystals is reported for photon energies just below the absorption edge (≈ 2.4 eV) at several temperatures between 80 and 300 °K. The investigation of the shape of the intrinsic absorption indicates the existence of an indirect gap. The influence of the higher concentration of conduction electrons on the indirect absorption edge of CdO has been studied. Extrapolation for n = 0 leads to the value Eig = (1.09 ± 0.04) eV.
Observation of dislocation arrays in low angle tilt boundaries in gold
Authors: Schober T. , Balluffi R. W.
Published: July 2007

Techniques were developed for studying the structure of low angle tilt boundaries by transmission electron microscopy. Boundaries were observed: 1) at normal incidence in bicrystals prepared by welding single crystal films together face‐to‐face at predetermined misorientations, 2) edge‐on in polycrystals obtained by the annealing of welded thin‐film bicrystals initially containing only twist boundaries. Symmetric (100) boundaries with [001] tilt axes consisted of either: a) arrays of uniformly spaced single edge dislocations running parallel to [001] with Burgers vectors b = a [100]; or b) arrays of uniformly spaced close pairs of dislocations running parallel to [001] with the dislocations in each pair having b = a/2 [110] and b = a/2 [110]. A choice between possibilities a) and b) could not be made on the basis of either the experimental observations or simple energy considerations. Symmetric (110) boundaries with [001] tilt axes consisted, as expected, of arrays of single edge dislocations parallel to [001] with b = a/2 [110]. Dislocation structures in (100) and (110) boundaries which possessed particularly small tilt angles and tilt axes lying along directions other than [001] in the boundary plane were also studied. In many cases, when the tilt axes were in certain favorable ranges of orientation, the dislocations broke up into segments in the boundary planes along directions which allowed them to dissociate on {111} planes into partial dislocations and stacking fault ribbons.
Influence of hydrostatic pressure on the electrical conductivity of tellurium single crystals
Authors: Becker W. , Fuhs W. , Stuke J.
Published: July 2007

The influence of hydrostatic pressure up to 5000 kp/cm2 on the electrical conductivity of differently doped tellurium single crystals is investigated in the temperature range from 165 to 430 °K. For extrinsic and intrinsic tellurium the conductivity increases exponentially with pressure. The pressure coefficient π = d (In σ)/dp is independent of temperature in the extrinsic region, rises appreciably then and finally decreases proportional to 1/T in the intrinsic range. The decrease of the energy gap with pressure at a rate of dEg/dp = −1.3 × 10−5 eV cm2/kp is the major effect in the intrinsic region. Possible mechanisms for the pressure dependence in extrinsic tellurium are discussed. It is shown that a decrease of the effective mass with pressure cannot account for the experimental results and that probably an enhancement of the dielectric constant by pressure leads to the observed increase of the mobility.
Optical properties of transition metal impurities in CdSe. I. Crystal‐field spectra
Authors: Langer J. M. , Baranowski J. M.
Published: July 2007

The absorption spectra of Ti (d2), V (d3), Cr (d4), Fe (d6), Co (d7), Ni (d8), and Cu (d9) in CdSe crystals are presented. The main features of the spectra are successfully interpreted using crystal‐field theory for the states of 3dn configuration in a potential of predominantly Td symmetry. It is found that the oscillator strengths of the observed absorption bands are in the range 10−2to 10−5 due to transitions within the 3dn shell. The crystal‐field parameters, Δ, and the Racah parameters, B and C, are determined where possible, and discussed.
Mössbauer effect studies of 9.3 keV transition in solid krypton
Authors: Mahesh K. , Sharma N. D.
Published: July 2007

Cubic structure calculations for the temperature dependence study of the recoilless fraction and the Mössbauer energy shift of Kr83m−9,3 keV transition are made using the quasiharmonic rigid‐atom model of the Kr‐lattice vibrations which includes the fourth nearest neighbour central force interactions. The results are compared with the experiment and the Debye model of the phonon spectra. The possibility of the low frequency Kr‐spectra not being Debye‐like is considered and the effect of the lattice anharmonicity is negligible. The characteristic temperature θM (0 °K) of the solid Kr is found to be 25 °K which is in agreement with the experiments.
The temperature dependence of the optical nonlinear susceptibility of sodium nitrite
Authors: Vogt H. , Happ H.
Published: July 2007

Information about the order‐disorder transition of NaNO2 is obtained from the temperature dependence of the optical nonlinear susceptibility χ(2). The decrease of χ(2)(T) in the ferroelectric phase can be related to increasing rotational motion of the NO‐ions. While χ(2) indicates the degree of order within the NO‐sublattice, the spontaneous polarization Ps may be regarded as an order parameter of the Na+‐sublattice. The difference between Ps(T) and χ(2)(T) is explained by a different order‐disorder behaviour of the Na+‐and the NO‐ions.
Optical and transport properties of the magnetic semiconductor α‐RuCl3
Authors: Binotto L. , Pollini I. , Spinolo G.
Published: July 2007

The optical and transport properties in the paramagnetic phase of α‐RuCl3 are studied here for the first time. Values are reported for the dc conductivity of single crystals over the temperature range 110 to 500 °K in the two crystallographic directions, along and perpendicular to the optic c‐axis: at 300 °K, ϱ∥c = 8 × 106 Ωcm and ϱ⟂c = 1.7 × 103 Ωcm. The activation energy for both directions is ≈ 0.1 eV below 300 °K and ≈ 0.5 eV for temperatures above 400 °K. Detailed absorption spectra in the energy range 0.1 to 4 eV, and in the temperature interval 80 to 300 °K, reveal three weak bands (α ≈ 103 cm−1) at ≈ 0.28, 0.53, and 0.75 eV, two stronger peaks (α ≈ 104 to 105 cm−1) at ≈ 1.18, 2.08 and a step at 3.10 eV (values at 80 °K). Reflectivity measurements in the energy range 1 to 9 eV show maxima which, at 300°K, are centred at ≈ 1.1, 1.9, and 3.10 eV and a marked reflection peak, at ≈ 5.10 eV, probably related to p(Cl) → s(Ru) band‐to‐band transitions. Ac photoconductivity spectra in the 0.6 to 2.8 eV region show structures closely related to the absorption bands in the same energy range. The different temperature dependence of the absorption and photocurrent spectra over the 80 to 300 °K interval is discussed. After an analysis of the transport data, the absorption spectrum up to 3 eV is discussed in terms of the Tanabe and Sugano diagram for a d5 configuration.
On the deformation potential constant of the conduction band in InSb
Authors: Tsidilkovskii I. M. , Demchuk K. M.
Published: July 2007

An analysis of experimental data for InSb is made and the deformation potential constant ϵ1 of the conduction band is determined. It is shown that the correctly calculated value of |ϵ1| is about 30 eV. In the calculations of the carrier mobility for heavily doped semiconductors it is essential to take into account the effect of the band nonparabolicity on the transition probabilities and the screening of the scattering potentials by conduction electrons, and additionally at high temperatures it is necessary to consider the influence of electronphonon interaction on the effective mass and energy gap. The small values of |ϵ1| reported by some authors, who studied transport phenomena at low temperatures, are obtained under the condition ħ/τ > kBT (τ is the time between successive collisions), i.e. when the theory used is invalid.
Dichroïsme circulaire magnétique de l'ion Eu2+ dans CaF2 et KCl (bandes larges)
Authors: Ferré J. , Billardon M. , Briat B.
Published: July 2007

Nous avons mesuré le dichroïsme circulaire magnétique de Eu2+ dans KCl et CaF2, à travers les bandes larges, dans le domaine spectral visible et proche ultra‐violet. Ces expériences ont permis de résoudre les deux bandes principales en leurs composantes spinorbite. Pour chaque bande, le niveau J = 5/2 a l'énergie la plus faible. Ce résultat est en accord avec certains travaux antérieurs.
The convergence of the orthogonalized plane wave method
Authors: Reser B. I. , Dyakin V. V. , Shirokovskii V. P.
Published: July 2007

The convergence of the OPW method is investigated systematically. An analytical estimate is given which shows that the convergence of the OPW method is rather weak. Numerical calculations of the energy band structure of diamond are done using a great number of OPW's (up to 900). The results show that even in this case a stabilization of the energy eigenvalues does not occur.
Temperature‐modulated reflectance of GaSe at the ground state exciton line
Authors: Balzarotti A. , Grandolfo M. , Somma F. , Vecchia P.
Published: July 2007

Thermoreflectance spectra in the exciton region were obtained on the layer compound GaSe. The experimental results can be explained by assuming that the only temperature effect is a shift of the whole structure. At liquid nitrogen temperature the values Eo = 2.093 eV and T = 41.0 meV are found for the first energy level and the broadening parameter, respectively. Measurements at three different temperatures gave the value dE0/dT = −5.49 × 10−4 eV/deg for the temperature coefficient.
Investigations of central crystal field effects on Ce3+ spectroscopic properties
Authors: Briffaut J. P.
Published: July 2007

The parametric central field has been applied to interpret successfully the changes of the 4f–5d energy gap of the Ce3+ ion in vacuum and in a ligand field. In addition, this model accounts for the stability of related 4f integrals with variations in the 4f–5d energy gap.
Fine structure of the extreme ultraviolet spectra of the potassium halide crystals at 10 °K
Authors: Blechschmidt D. , Haensel R. , Koch E. E. , Nielsen U. , Skibowski M.
Published: July 2007

The reflection spectra of KCl, KBr, and KI single crystals and of a KF film have been measured below 10 °K for photon energies between 10 and 30 eV using synchrotron radiation. The numerous new spectral features at low temperature are discussed in terms of electronic transitions from the valence band and from the K+3p level. Due to spin‐orbit interaction of the K+3p level the Γ‐K+3p core exciton at about 20 eV is split into two lines with an energy separation of about 0.2 eV for all halides. The observed fine structure and a comparison with a calculated conduction band density of states in the case of KI support the excitonic nature of the Γ‐X K+3p doublet.
Overlap and covalent contributions to the crystal field splittings in CaF2:Tm2+
Authors: Anisimov F. , Dagys R.
Published: July 2007

The crystal field splittings in CaF2:Tm2+ were calculated within the framework of the complex (TmF8)6−. By separating the overlap from covalent contributions, the overlap effects were found to dominate. It is shown that ligand‐ligand overlap effects are important. On the contrary, the role of 5s2 5p6 ligand overlap is fairly small. Satisfactory agreement between the values of the splittings calculated and the observed ones is obtained.
Multi‐photon interband optical transitions in crystals
Authors: Kovabskii V. A. , Perlin E. Yu.
Published: July 2007

A method is developed to derive expressions for n‐photon interband transition rates with arbitrary n, in which the real crystal energy spectrum, is taken into account. For particular cases the results of the theory under consideration coincide both with the perturbation theory and semiclassical treatment [13 to 16]. The effect of the radiation coherent properties on the multi‐photon processes is discussed. Contrary to previous calculations it is possible to give a qualitative explanation of the experimental data [4, 6].
The phonon polarization operator in a ferromagnet at low temperatures
Authors: Kashcheev V. K.
Published: July 2007

The imaginary part of the phonon polarization operator and the renormalization of the sound velocity due to the spin‐phonon interaction are calculated in a cubic ferrodielectric for large atomic spins in the spin‐wave temperature region.
Singlet exciton annihilation in anthracene crystals
Authors: Babenko S. D. , Benderskii V. A. , Goldanskii V. I. , Lavrushko A. G. , Tychinskii V. P.
Published: July 2007

The fluorescence quenching under high excitation intensities has been studied in anthracene crystals. The singlet–singlet annihilation constant of (1 ± 0.5) × 10−8 cm3 s−1 is calculated from the quenching of fluorescence induced by a nitrogen 16 ns pulse laser (λ = 3371 Å). The main process of quenching under longer illumination (2 × 10−5s) is the interection between singlet and triplet excitons with a rate constant of (7 ± 4) × 10−9 cm3s−1.
Hole mobility in trigonal SexTe1−x single crystals
Authors: Mell H. , Stuke J.
Published: July 2007

The weak‐field magnetoconductivity components σ1111, σ1122, and σ1133 of trigonal Se‐Te mixed crystals have been measured in the temperature range 80 to 300 K. An analysis of these data yields the hole mobility in the alloys. The temperature dependence of the mobility and the comparison with theoretical mobility values indicate that alloy disorder scattering plays an important role in the SeTe system. From the strength of alloy scattering an approximate value of 0.2 eV is obtained for the difference between the valence band energies of Se and Te.
Conduction band of IVa and Va subgroup transition metal monocarbides (II)
Authors: Borukhovich A. S. , Geld P. V. , Tskhai V. A. , Dubrovskaya L. B. , Matveenko I. I.
Published: July 2007

Results are presented of a study of the Hall effect (in the low‐temperature range 20 to 300 °K) and of the thermopower of the monocarbides VCx, NbCx, and TaCx within the limits of their homogeneity regions. Basing on the experimental results obtained and on earlier data on magnetic susceptibility and electric resistivity, the electronic spectrum of non‐stoichiometric monocarbides is discussed on the basis of presentations suggested in a previous paper [1].
Mössbauer study of the valence state of 57Fe after 57Co decay in CoFe2O4
Authors: Cruset A. , Friedt J. M.
Published: July 2007

The Mössbauer emission spectrum of 57Co in CoFe2O4 is reported. Electron capture leads to the formation of 57Fe3+ substituting 57Co2+. The stabilization of the aliovalent charge state is consistent with an electrostatic model.
Electron paramagnetic resonance study of Al2+ in BeO
Authors: Du Varney R. C. , Garrison A. K. , Harem S. B.
Published: July 2007

When single crystal BeO is X‐irradiated at room temperature, paramagnetic centers are formed. These centers are identified by EPR as electrons trapped at Al3+ impurities substitutional for beryllium ions. The g‐tensor is cylindrically symmetric with values g∥ = 2.003 and g⊥ = 2.004 with the axis of symmetry along an Al–O bond direction. The hyperfine tensor has the principal values Ax′x′ = 207.6 G, Ay′y′ = 175.7 G, and Az′z′ = 176.6 G. The x′‐ and z′‐directions lie in a plane which contains the polar or c‐axis and the Al–O bond direction. The z′‐axis makes an angle of 14° with the c‐axis. Also, an absorption spectrum in γ‐irradiated Thermalox 995, a commercial form of sintered BeO ceramic used in thermally stimulated exoelectron emission radiation dosimeters, is analyzed and shown to be the powder pattern of this aluminum impurity center.
X‐ray dilatometric study on ferroelectric phase transition of KH2PO4 I. The order of transition
Authors: Kobayashi J. , Uesu Y. , Enomoto Y.
Published: July 2007

X‐ray dilatometric measurements have been made on lattice strains along the A‐ and B‐axes of KH2PO4 as a function of temperature and biasing electric field near the Curie point. It has been clearly observed that the forced ferroelectric transitions take place in a very small but definite temperature range of 0.65 deg. A phenomenological treatment has been developed, and the coefficients of the elastic Gibbs function of KH2PO4 have been successfully determined to γ = −1.19 × 10−10 e.s.u. and Δ = 1.10 × 10−18 e.s.u., where γ stands for the coefficient of the P4 term and Δ for that the of P6 term. γ is negative. These values explain well the reported spontaneous polarization and dielectric stiffness when strong tendency to coexistence of two phases at the transition is duly allowed for. From the observations it is concluded that the ferroelectric phase transition of KH2PO4 is unequivocally of first order.
On a criterion for antiferromagnetism connected with the metal–insulator phase transition
Authors: Elk K.
Published: July 2007

A simple model is discussed of the electron‐spin interaction in transition metal compounds which show a metal–insulator phase transition. Using this model, a criterion is derived to decide which of these compounds have an antiferromagnetic ground state.
A model calculation for the energy bands in the Hg1−xCdxTe mixed crystal system
Authors: Overhof H.
Published: July 2007

A KKR model is used to calculate energy bands in the Hg1−xCdxTe mixed crystal system near the fundamental band gap. The results are presented in terms of k · p bands according to Kane and compared to experimental k · p parameters for the conduction band. For the heavy hole bands constant energy contours are given in the (100), (110), and (111) planes.
Electroreflectance Spectra and Energy Band Structure of CdSnP2
Authors: Kavaliauskas J. , Karavaev G. F. , Leonov E. I. , Orlov V. M. , Chaldyshev V. A. , Šileika A.
Published: July 2007

The electroreflectance spectra of CdSnP2 chalcopyrite single crystals have been investigated in the spectral region 1.0 to 4.7 eV at room temperature using polarized light. The electroreflectance structure in the region of the fundamental absorption edge and its polarization dependence are found to be in good agreement with the relative location of the valence bands earlier predicted theoretically. A great number of electroreflectance peaks has been observed in the spectral region 2.4 to 4.7 eV and interpreted by optical transitions at the T, T, and N points of the Brillouin zone of the chalcopyrite lattice. The only transitions used were direct ones and responsible for the main structure in the optical spectra of sphalerite crystals. In addition, the fine structure of these optical transitions due to crystal field splitting has been included.
Berechnung der chemischen Verschiebung der Kernresonanz in AIII–BV‐Halbleitern
Authors: Hübner K.
Published: July 2007

Die Ramseysche Theorie der chemischen Verschiebung der Kernresonanz wird auf den Fall, daß Energiebänder vorliegen, ausgedehnt und unter Benutzung des Kaneschen Bandstrukturmodells und der Kenntnisse über die chemische Bindung auf die Berechnung der Resonanzverschiebung in AIII–BV‐Halbleitern angewendet. Eine Erklärung der aus der Literatur bekannten experimentellen Verschiebungen wird erst durch Berücksichtigung von d‐Elektronen möglich. Die auftretenden Einzentrumintegrale werden mit Hilfe modifizierter Slater‐Funktionen, die Zweizentrenintegrale mit normalen Slater‐Funktionen berechnet.
A Spin‐Flip Effect in FeSn
Authors: Ligenza S.
Published: July 2007

A combined investigation is made of Müssbauer effect and neutron diffraction on powdered samples of FeSn in the temperature range between 4.2 and 400 °K. A spin‐flip effect is found at about 70 °K. Two non‐collinear models of spin ordering are proposed, one above and one below the transition temperature. The magnetic unit cell with a × 2 a ×× 2 c is found at both sides of this transition. It is concluded that the main spin direction at T < 70 °K is along [100] and at 70 °K ≪ T < TN along [210]. The atomic magnetic moment of Fe is obtained to (1.78 ± 0.06) μB at liquid helium temperature.
Local Excitons and Exciton Band Structure in Naphthalene
Authors: Ostapenko N. I. , Sugakov V. I. , Shpak M. T.
Published: July 2007

Positions of the electron levels of the local exciton energy in a naphthalene crystal doped with thionaphthene, indole, and benzofurane are calculated. The guest molecule is assumed to change the excitation energy of one host molecule nearest to the impurity. Also it is considered that the main contribution to the exciton dispersion law comes from the matrix elements of resonance interaction between nearest naphthalene molecules which are in inequivalent positions in the ab plane of the crystal. Good agreement between the theoretical and experimental values favours the validity of the chosen local centre model and exciton dispersion law employed.
Application of the Fourier Method for Calculations of the Lattice Distortion Around a Vacancy in Copper and Silver. Pseudopotential Approach
Authors: Chevychelov A. D.
Published: July 2007

On the basis of the physical assumptions formulated in [1] the precise calculation of a lattice distortion around a vacancy in Cu and Ag is performed using the static Fourier method. The obtained result is compared with that of [1] and with the calculations of Bullough and Hardy [9].
Interpretation of the Widths of SEM Electron Channelling Lines
Authors: Schulson E. M.
Published: July 2007

From a two beam approximation of the dynamical theory of the relative backscattered electron intensity as a function of direction of incidence, it is shown that the angular width of electron channelling lines on SEM images can be given by the expression: 2 ωg = 2/ξg|g|, where ξg and g are the extinction distance and the reciprocal lattice vector respectively of the strongly excited reflection. The expression is verified by comparing calculated line‐widths with measured widths from silicon as a function of incident beam energy and reflection excited. An appendix is given discussing quantitatively the degradation effects of beam divergence on electron channelling lines. It is suggested that line broadening might be a possible method for assessing lattice distortions.
Concentrational Phase Transition in Solid Solutions of Titanium and Chromium Sesquioxides (Cr2–xTixO3)
Authors: Geld P. V. , Zubkov V. G. , Matveenko I. I.
Published: July 2007

On the basis of the results of magnetic susceptibility, neutron scattering, and thermopower investigations it is shown that anomalies in the isotherms of μeff., μz, and in the thermoelectric coefficient of magnetic semiconductors may be explained assuming that a concentrational phase transition takes place. In solid solutions of the type Cr2–xTixO3 this phase transition is accompanied by the conversion of the collinear antiferromagnetic structure into a noncollinear antiferromagnetic one.
Recombination of Impact Ionized Excess Carriers in Tellurium
Authors: Bringer A. , Nimtz G.
Published: July 2007

The recombination time of p‐type tellurium was measured dependent on carrier mobility and carrier density at 77 K. Excess carriers were produced by impact ionization in strong electric fields to achieve large excess carrier concentrations. The recombination of the excess carriers was observed by the help of microwaves, the rise time of the experimental apparatus was less than 5 × 10−9 s. The experimental data can be interpreted as the superposition of a slow and a fast exponential decay. The results can be explained by an extended Shockley‐Read model. The energy level and the concentration of the trapping and recombination centers can be deduced from the experimental data.
Work‐Hardening and Surface Investigations on Copper Single Crystals Oriented for Multiple Glide
Authors: Vorbrugg W. , Goetting H. Ch. , Schwink Ch.
Published: July 2007

For copper single crystals with axis orientations [110], [111], and [100] work‐hardening curves and surface phenomena were studied at various temperatures. Analogous to single glide crystals we succeeded in dividing the curves into different stages and correlating them with characteristic slip line patterns. [110] crystals show the same work‐hardening behaviour as single glide crystals, contrary to [111] and [100] ones where multiple glide is fundamental. The result of a quantitative analysis of the slip line photographs is that apparently for all orientations the same work‐hardening mechanisms are operating. However, in [111] and [100] crystals cross‐slip seems to occur in a way different from that in single glide crystals.
Electron Magnetic Susceptibility, Paramagnetic Resonance, and the Band Structure of Silicon‐Rich n‐Type Silicon–Germanium Alloys
Authors: Geist D.
Published: July 2007

The lattice susceptibility appropriate to the silicon content has been subtracted from the total susceptibility. The remaining carrier contribution is dependent on the effective mass parameters and the g‐value. Using g ≈ 2, extrapolated from measured electron paramagnetic resonance (EPR) values and assuming six ellipsoidal energy surfaces with K = m∥︁/m⟂ = 4.68, the mass m⟂ is found to be about m⟂ = 0.27 m (m free electron mass), a value lying close to that for silicon. This result indicates that the band structure as a whole in the neighbourhood of the Δ1 minimum changes only slightly going from 100% silicon to the range between 80 and 65% silicon in silicon–germanium alloys.
Impurity Absorption in GaP Doped with Copper and Oxygen
Authors: Olsson R.
Published: July 2007

Optical absorption due to impurities was investigated in homogeneous GaP crystals at room temperature. The transmission of light through the crystal is influenced by a simultaneous additional illumination of light with different wavelength. This light changes the occupancy of an impurity level. A simple theory is presented, which relates this change in transmission of light to the absorption coefficient due to an impurity and also to the optical cross sections of the impurity level involved. The curves for the transmission change were compared with photocurrent quenching spectra measured on the same sample. The absorption coefficient was measured directly in the range 0.5 to 2.3 eV. The relative change in transmission was large in some samples (up to 10%), but had such a slow relaxation, that steady light had to be used. Absorption edges at 0.64, 0.70, 0.8, and 0.9 eV were found and their origins are discussed. The properties of some of the absorptions were found to be consistent with those expected from an acceptor impurity state with a dn electron configuration.
Interband Exchange and the Excitonic Instability
Authors: Kübler J.
Published: July 2007

A calculation of the electronic dielectric function (DF) in semiconductors with small energy gaps is presented that takes into account the screened Coulomb and exchange interaction between electrons and holes. Depending on the sign of the exchange term, the DF is either given approximately by its well‐behaved background value or is strongly enhanced over the RPA result when the gap is decreased to zero. Consequences for the excitonic instability are elaborated.
ESR and ENDOR Investigation of Interstitial Hydrogen Atoms in Alkali Halides. II. Theoretical Interpretation
Authors: Spaeth J. M. , Seidel H.
Published: July 2007

A theoretical interpretation of the superhyperfine interactions, the proton hyperfine interaction, and the g‐factor of H centres in KF, KC1, KBr, NaCl, and RbCl is presented. The anisotropic distribution of the hydrogen electron into the lattice is well explained by a wave function which was obtained by orthogonalization of the hydrogen Is function to an internally orthogonal set of crystal ion orbitals. A slight covalency to the nearest halogen neighbours is taken into account. The g‐factor can also be understood on the basis of this wave function, if the electronic as well as the charge transfer excited states are considered. In order to explain the proton hyperfine interaction the influence of van der Waals forces has to be included.
The Temperature, Pressure, and Concentration Coefficients of Resistivity of Metals and Their Relation to the Diffusion Thermopower
Authors: Barnard R. D.
Published: July 2007

The resistivity of metals has been considered in the light of modifications to the Fermi energy, Debye temperature, and band structure brought about by changes of pressure, temperature and impurity concentration. The changes of Fermi energy have been formulated in terms of the diffusion thermopower provided the electron scattering is quasi elastic. A new relation between the temperature coefficients of resistivity at constant pressure and constant volume is established and verified for the alkali metals. The implications of the resistivity corrections to the study of deviations from Matthiessen's rule are also discussed.
Theory of Vibronic Spectra in Molecular Crystals with Four Molecules in the Unit Cell: Perylene
Authors: Witkowski A. , Zgierski M. Z.
Published: July 2007

A theory of vibronic coupling in molecular crystals which – like perylene – contain four molecules in the unit cell is presented. The vibronic Hamiltonian, selection rules, and expressions for the integral properties of an absorption spectrum are derived and discussed. The vibronic equation contains parameters which as shown can be obtained from the widths and location of the gravity centres of the vibronic absorption bands. The absorption spectra computed from the vibronic equation derived agree well in both frequency and intensity distribution with the observed crystal absorption bands of different polarization. All main features of the absorption bands in the perylene crystal result from vibronic coupling only and inclusion of charge transfer states is not necessary.
Theory of the Elastic and Inelastic Scattering of Light by Magnetic Crystals. I. First‐Order Processes
Authors: le Gall H. , Jamet J. P.
Published: July 2007

A quantum description of the different magneto‐optical interaction is obtained using the second quantization notation in the spin‐dependent dielectric Hamiltonian of the crystal. It is shown that the Faraday, Kerr, Cotton‐Mouton, and spin Raman effects due to paraor ferromagnetic spins, which generally in the literature appear as distinct processes, may be described actually with a common spin–photon interaction Hamiltonian. From this Hamiltonian the magneto‐optical interactions may be separated into two groups corresponding to either an elastic or an inelastic spin‐photon scattering. The physical and analytical relations between these interactions, the general properties of susceptibilities, and polarization rules are deduced from the microscopic concept of the scattering of photons by magnetic crystals. It is shown that the Faraday effect, which is usually investigated from the circular birefringence of a macroscopic field, can be described as an elastic scattering of photons with a π/2 spatial rotation of their polarization vectors.
A New Relaxation Mechanism of the Exchange Bounded Paramagnetic Centres
Authors: Glinchuk M. D. , Deigen M. F. , Suslin L. A.
Published: July 2007

The time of the spin‐lattice relaxation of exchange bound paramagnetic ions due to the modulation of their electric fields by lattice oscillations is calculated. The contribution of the mechanism suggested to the relaxation is essential in crystals where the constants of the electron‐spin coupling are large. As an example the relaxation time of paramagnetic centres in crystals with Td symmetry is evaluated.
Thermal Broadening and Shift of the Zero‐Phonon Lines in Optical Spectra of Impurity Organic Crystals
Authors: Sapozhnikov M. N.
Published: July 2007

A theoretical interpretation is made of all the data on the temperature broadening and shift of the zero‐phonon lines in spectra of impurity normal paraffin crystals. It is shown that the broadening of most lines investigated may be well described in the Debye approximation using the theoretical dependence, obtained on the basis of the Krivoglaz‐McCumber model in which adiabatic, Condon and harmonic approximations were utilized, and a small change of the elastic constants of the lattice vibrations and a displacement of the equilibrium positions of nuclei induced by the electron transition in the impurity centre were taken into account. The line shifts could not be described by the theoretical formula obtained in the same approximation. The possible reasons of this discrepancy are discussed.
Neutron Diffraction and Susceptibility Measurements on ErPO4 and ErVO4
Authors: Will G. , Lugscheider W. , Zinn W. , Patscheke E.
Published: July 2007

Powder neutron diffraction measurements were performed on ErPO4 and ErVO4 at temperatures as low as 2 K and in external magnetic fields up to 30 kOe. No magnetic ordering could be detected. The ensueing susceptibility measurements and an estimate of the magnetic dipole interactions lead to an transition temperature of about 0.8 K, with the interaction being probably purely dipolar with negligible exchange interaction.
Dielectric Properties of the Rubidium Halide Crystals in the Extreme Ultraviolet up to 30 eV
Authors: Peimann C. J. , Skibowski M.
Published: July 2007

The reflectivity of freshly cleaved single crystals of RbCl, RbBr, and RbI and of an evaporated RbF film was measured at room temperature for photon energies between 10 and 30 eV using synchrotron radiation. With a resolution of 2 Å over the whole spectral range considerable new spectral features were observed in the region where high energy valence band transitions occur and electrons from the first core level, the Rb+ 4p level, are excited. For all Rb halides excitation of the Rb+ 4p level starts at about 16 eV with an exciton multiplet which can be explained as being due to spin‐orbit splitting of the core level and to critical points at Γ and X in the conduction band. The energies of the multiplet are compared to transition energies of the 4p electrons of the free Rb+ ion. The complex dielectric constant, the absorption coefficient, and the energy loss function are derived from the reflectivity by means of a dispersion analysis. The results are compared with absorption and electron energy loss experiments on evaporated polycrystalline films.
Crystal Dynamics of Cesium Iodide
Authors: Bühner W. , Hälg W.
Published: July 2007

Frequencies of the normal modes of vibration of cesium iodide at room temperature propagating in certain symmetry directions were determined by means of slow‐neutron inelastic scattering using a triple axis spectrometer. The data are in reasonable agreement with thermal diffuse X‐ray scattering investigations of Eldridge [1]. The shell model was fitted to the frequencies with good results. This 14‐parameter model was used to compute a frequency distribution and related thermodynamic data.
Low temperature specific heats and related thermodynamical functions of neodymium dihydride NdH2.00. crystal field effects
Authors: Biegański Z.
Published: July 2007

The heat capacity of neodymium dihydride NdH2.00 was measured over the low‐temperature range by adiabatic calorimetry. At 298.15 K the measured heat capacity at constant pressure (Cp), the entropy (S0), the enthalpy function (H0–H), and the Gibbs function–[(F0–H)/T] are: 10.29 cal mol−1 deg−1, 14.08 cal mol−1 deg−1, 1882 cal mol−1, and 7.76 cal mol−1 deg−1, respectively. The influence of the crystal field of cubic symmetry on the splitting of the ground level 4I9/2 of the Nd3+ ion was analysed, and the conclusion was drawn that the quartet Γ is the lowest‐lying level. This supports the idea of the anion‐like character (hydridic model) of hydrogen in this hydride.
Paramagnetic resonance of Yb3+ and Nd3+ in YPO4
Authors: Hillmer W.
Published: July 2007

Paramagnetic resonance of trivalent ytterbium and neodymium in single crystals of yttrium phosophate has been investigate at K‐band frequencies and temperatures of 1.7 and 4.2 K. Spin‐Hamiltonian parameters including the hyperfine constants for Yb171 and Yb173 and the ground state eigenfunctions were determined.
Paramagnetic resonance of Er3+ in YPO4
Authors: Dzionara M. , Kahle H. G. , Schedewie F.
Published: July 2007

The paramagnetic resonance of trivalent erbium in single crystals of yttrium phosphate has been observed at 4.2 K. The spectrum is described in terms of the appropriate spin‐Hamiltonian.
Optical properties of boron carbide and comparison with β‐rhombohedral boron
Authors: Werheit H. , Binnenbruck H. , Hausen A.
Published: July 2007

The optical absorption spectrum of B12C3 exhibits an indirect interband transition with onset at h ω = (0.48±0.03) eV. In the subsequent region of lower absorption (α ∼ 400 cm−1) traps of great density are essentially effective for the optical properties. The lattice vibration spectrum starting at 4 μm has oscillations at 6.55, 9.25, 10.5, 11.9, 14.4, 17.3, and 25.4 μm. A monotonic increase of the reflectivity occurring at wavelengths λ > 30 μm can be assigned to the strongly damped plasma resonance of free holes. The comparison with the properties of β‐rhombohedral boron indicates distinct similarities.
On the temperature factors of tetragonal and Cubic BaTiO3
Authors: Aberdam D.
Published: July 2007

A calculation is made of the temperature factors of tetragonal and cubic BaTiO3 at room temperature and in the range between 395 and 925°K. This calculation is based on the recently available data on the phonon dispersion spectrum of BaTiO3. The deviation from the Debye model for the acoustical modes contribution, high‐frequency optical modes contribution, and the dispersion anisotropy of the low‐frequency transverse optical modes are taken into account. Our results are in reasonable agreement with the data obtained from neutron structure analysis for the titanium and the barium ions, and support Hüller's model of the dispersion anisotropy of the soft modes.
Analysis of point defect states in copper. IV. Interstitial cluster formation at 93 K
Authors: Becker D. E. , Dworschak F. , Wollenberger H.
Published: July 2007

Damage rate measurements have been performed by irradiating copper samples of different purity with electrons at 93 K up to defect concentrations of about 10−4. The results are interpreted in terms of interstitial cluster formation. The clusters are nucleated at impurities.
A theoretical calculation of the orbital g‐factor of the excited state of F‐centres in alkali halides
Authors: Thuau M. , Margerie J.
Published: July 2007

Using a model similar to that of Smith [4] the orbital g‐factor gorb. of the excited state of F‐centres in LiF, LiCl, NaF, NaCl, KF, and KCl was calculated. The results are quite sensitive to the particular envelope wavefunction chosen for the F‐centre. Gourary and Adrian type II wavefunctions lead to results which are in good agreement with the available experimental values.