bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoelectric and Thermomagnetic Properties of n‐Ge in the Region of Phonon Drag Effects
Authors: Lutsyak V. S. , Nitsovich V. M.
Published: July 2007

The influence of phonon drag effects on thermoelectric and thermomagnetic properties of n‐Ge is investigated. The role of different scattering mechanisms is discussed. From a comparison of the experimental data [11, 13] with the theory follows that the theoretical values of the thermoelectric and thermomagnetic coefficients agree better with experimental ones assuming that the phonon relaxation times depend on the wave vector and temperature as it was predicted by Simons [2].
Anisotropy of Paramagnetic Spin‐Lattice Relaxation
Authors: Aminov L. K. , Klimachev A. F.
Published: July 2007

Simple group‐theoretical arguments are used to derive the dependence of the relaxation transition probabilities with participation of an arbitrary number of phonons on the orientation of an external magnetic field relative to the crystal axes of the paramagnetic samples. The system of paramagnetic ions with arbitrary spin is investigated in the case of weak magnetic field, when the Zeeman splitting is much smaller than the crystal field splitting. However, the results may be directly transferred to the opposite case of |𝒳z|≫|𝒳cr|. An example of application of the results obtained is considered.
Correlation of Infra‐Red Spectra with Structural Distortions in the Spinel Series Mg(CrxAl2−x)O4
Authors: Grimes N. W. , Collett A. J.
Published: July 2007

The details of the infra‐red spectra over the range 200 to 1000 cm−1 are presented for eight members of the spinel series Mg(CrxAl2−x)O4 and correlated with the development of local distortions of C3v symmetry. It is shown that the frequency behaviour of two of the prominent absorption bands is described rather well by the equations given by Waldron for the modes labelled v1 and v3. Force constants k1 and k0, corresponding to unit displacements along the tetrahedral cation‐oxygen and octahedral cation‐oxygen bonds, respectively, are derived in a manner which allows for the presence of other interactions.
Computer Simulation of Electron Microscope Images
Authors: Maher D. M. , Perrin R. C. , Bullough R.
Published: July 2007

A procedure has been developed which enables computer‐simulated electron micrographs of defects in crystalline foils to be constructed that are, photographically speaking, virtually indistinguishable from the corresponding experimental micrographs. The intensity variations in the image are simulated by constructing a suitable matrix of overprinted “dots” on the output of a Stromberg‐Carlson 4060 plotting device. These variations are quantitatively calibrated in the final micrograph against the corresponding optical densities. The number of grey levels generated by a given set of computer and photographic variables is sufficiently large to provide excellent tonal separation in the final simulated image and high resolution micrographs are readily achieved.
Dislocations in symmetric high angle [001] tilt boundaries in gold
Authors: Schober T. , Balluffi R. W.
Published: July 2007

The structure of high angle tilt boundaries possessing small tilt deviations (i.e., 1 to 2°) from various special high coincidence site density tilt misorientations was studied by transmission electron microscopy. The latter misorientations corresponded to rotations of θc = 22.6, 28.1, 36.9, 53.1, 61.9, 67.4, and 73.7° around [001]. The grain boundary planes were of the symmetric type, and the tilt deviations from the high coincidence site density misorientations were around various axes lying in the grain boundary planes. The boundaries were examined at normal incidence in bicrystals prepared by welding single crystal thin films together face‐to‐face at predetermined misorientations and also edge‐on in polycrystals obtained by the annealing of welded bicrystals initially containing only twist boundaries. Arrays of parallel dislocations were found in a number of boundaries which appeared to be in good agreement with the structures predicted by use of Bollmann's analysis of the geometry of dislocations in high angle grain boundaries. It is therefore concluded that the structure of such high angle boundaries consists of an array of evenly spaced edge dislocations (or possibly close pairs of dislocations in certain cases) running parallel to the tilt deviation axis embedded in the interface corresponding to the nearby high coincidence site density misorientation. It seems likely that such structures exist over wider ranges of misorientation than were investigated experimentally.
Temperature dependence of the EPR line width and a relaxation of Cr3+ ions in ZnWo4
Authors: Bugai A. A. , Glinchuk M. D. , Deigen M. F. , Maksimenko V. M.
Published: July 2007

The change of the EPR line width, shape, and angular dependence of the halfwidth of Cr3+ ions in ZnWO4 is investigated in the temperature range from 4.2 to 1200 °K. It is shown that the EPR line broadening at high temperatures is due to the spin‐phonon interaction. Two‐ and four‐phonon processes of Raman‐type play the main part in relaxation. Experimental data on high‐temperature line broadening are used to evaluate the spinlattice relaxation time at liquid helium temperature.
Elektronen‐störpotential inhomogen verzerrter kristallgitter
Authors: Teichler H.
Published: July 2007

Mit Hilfe der Wannier‐Formulierung wird ein effektives Störpotential aufgestellt, das den Einfluß endlicher, inhomogener Gitterverzerrungen auf die elektronischen Eigenschaften der Metalle beschreibt. Linearisierung in den Verschiebungsdifferenzen führt auf ein Störpotential, das vollständig durch Matrixelemente zwischen den Wannierfunktionen des ungestörten Kristalles und den Verschiebungen definiert ist.
Plural and multiple scattering of low‐energy heavy particles in solids
Authors: Meyer L.
Published: July 2007

Small‐angle multiple scattering of low‐energy heavy particles (Born parameter α > 1) in solid layers is calculated, using a scattering cross section derived from classical mechanics. The angular distribution of the scattered particles is given as a sum of two functions, which are tabulated. The calculated distributions coincide with those of the well‐known theory of Molière for large thicknesses of material. For small thicknesses there are profound deviations.
On the effect of exchange interaction on the impurity ion optical spectrum
Authors: Nikiforov A. E. , Cherepanov V. I.
Published: July 2007

The method of effective Hamiltonian (EFH) is applied to the excited state (2E4A2) fine structure of Cr3+–Cr3+ fourth order pairs in ruby. Comparison with experimental data illustrates the importance of both the anisotropic and antisymmetric exchange interactions, and that part of isotropic exchange interaction, which is nondiagonal in the orbital variables. Various microscopical mechanisms responsible for terms in the effective Hamiltonian are discussed.
Calculation of the induced magnetic anisotropy energy by means of Boltzmann statistics
Authors: Steinert J.
Published: July 2007

Induced magnetic anisotropies are caused by changes of orientation or concentration of crystal defects. All possible sites of a defect will be got in a given crystal by application of elements of the point group which corresponds to the crystal class. In cubic crystals possible changes of the concentration of the defects due to the direction of magnetization does not influence neither the induced unidirectional nor the induced uniaxial anisotropy, but influence the induced biaxial anisotropy.
Le champ moléculaire du nickel
Authors: Munschy G.
Published: July 2007

En tenant compte des fluctuations de l'ordre magnétique dans la théorie de l'électron collectif de Stoner, on montre que le champ moléculaire hm(M) n'est pas proportionnel à l'aimantation M du métal ferromagnétique, mais qu'il comporte des termes correctifs en M3, M5, … Dans le cas du nickel, le champ obtenu est en assez bon accord avec les prévisions semi‐empiriques de Shimizu.
Some consequences of surface and size effects in plastically deformed copper single crystals
Authors: Mughrabi H.
Published: July 2007

The dislocation behaviour in deformed copper single crystals was previously shown to correspond to a lower local flow stress in the surface region than in the interior and the primary glide plane was found to undergo a characteristic bending in the surface region, reflecting a local excess density of unpaired edge dislocations. The detailed features of this “profile” are explained by a dislocation model which takes into account both surface and inner dislocation sources. It is shown that, as a result of the surface effects, dislocation glide paths in stage II as determined from slip lines are about 2.5 times larger than those in the interior. The rate of work‐hardening in stage II above a certain stress level, however, is found to be fairly constant over the cross‐section inspite of surface effects. It is concluded from Seeger's stage II work‐hardening theory that the number of dislocations per group should therefore decrease in the same way as the glide paths from the surface towards the interior. This prediction is in line with available experimental data. The shape of the macroscopic stress‐strain curve is explained by the local microscopic behaviour. Our results are consistent with Fourie's concept of preferential core‐hardening. The possibility of preferential near‐surface‐hardening is indicated.
The fine structure of beams in electron diffraction emerging from wedge‐shaped crystals. Multiple beam case
Authors: Serneels R. , De Ridder B. , Gevers R. , Amelinckx S.
Published: July 2007

The fine structure of electron diffraction beams emerging from a wedge‐shaped crystal is analysed on the basis of the dynamical multiple beam theory. First the basic principle of the Fourier‐transforms method and the method of the scattering matrix is summarized. The theory is applied to a wedge as well in a particular as in a general orientation. Assuming n strongly diffracted beams it is found that the transmitted and each strongly diffracted beam is composed of n + 1 sub‐beams with slightly different orientations. The geometry of the fine structure configuration is discussed and the influence of absorption effects on the intensity of the beams is examined. It is emphasized that the intensity of the different sub‐beams is directly related to the strength of excitation of the different Bloch wave fields in the crystal. The method is discussed explicitly for a particular multiple beam situation in MgO where the 400 reciprocal lattice vector is in the exact Bragg orientation and where only systematic reflections are supposed to be active. Taking account of absorption effects the situation is discussed within the three beam dynamical theory (000, 200, 400). Afterwards the influence of the systematic interactions (600, 500) is investigated. Three‐ and five‐beam calculations are compared with experiments. It is found that the observed fine structures (of the different beams) can be explained adequately by three‐beam theory.
Superconductivity in simple metals
Authors: Rajput J. S.
Published: July 2007

The superconducting state parameters for both nonsuperconductors and simple‐metal (nontransition‐metal) superconductors are evaluated using the exact OPW (orthogonalized‐plane‐wave) form‐factors based on the model pseudopotential of Heine and Abarenkov. An attempt is made to establish a criterion for the occurrence of superconductivity in non‐transition metals using the pseudopotential approach and it is inferred that more reliable values of the superconducting state parameters can be obtained using a correct pseudo‐potential and the phonon spectrum.
Dependence of magnetically induced anisotropy in a ferromagnetic single crystal on its block structure
Authors: Lesnik A. G.
Published: July 2007

A general expression for the energy of induced anisotropy in ferromagnetic single crystals, obtained in a previous paper [1] is analyzed in detail. It is shown that the induced anisotropy constant Ku depends on the single crystal block structure and the direction of magnetic field during annealing.
Determination of structure factors of X‐rays using half‐widths of the Bragg diffraction curves from perfect single crystals
Authors: Kikuta S.
Published: July 2007

For determining precisely the absolute values of X‐ray atomic scattering factors (f‐values) the half‐widths of the Bragg diffraction curves of perfect single crystals are utilized. The principle of the method and the experimental procedure are described. Using a double‐crystal diffractometer of parallel setting with CuKα1 radiation, the f‐value for the 422 reflection of silicon was determined with an accuracy better than 0.3% in a favourable case, which is in good agreement with the theoretical one. Even strongly absorbing crystals can be used as specimens, a size of the perfect region of about 0.5 mm will be sufficient for the measurements. The present method seems to be promising.
Ferromagnetic resonance in single crystal nickel disks: Angular dependence of linewidth
Authors: Anderson J. R. , Bhagat S. M. , Cheng F. L.
Published: July 2007

The angular variation of the FMR linewidth in single crystal disks of nickel has been studied for both the in‐plane (H) ∥ sample surface) and out‐of‐plane (H ⊥ sample surface) geometries. For the in‐plane case the linewidth is essentially isotropic. For the out‐of‐plane geometry the effective linewidths exhibit a shallow minimum for M about 55° from the sample plane. For both geometries these results are consistent with a Gilbert type equation (including exchange conductivity effects) with an angle independent damping parameter.
Elastic Electron Scattering in InSb‐Type Semiconductors
Authors: Zawadzki W. , Szymańska W.
Published: July 2007

Relaxation times for elastic electron scattering in III–V compounds of InSb type are calculated taking into account consistently the nonparabolic structure of the conduction band, both in the density of states and electron wave functions. The calculations are based on the Kane model of band structure, including explicitly mixing of p‐like components into the total wave function of the conduction band. Electron scattering by charged impurities and heavy holes, optical phonons (polar interaction), acoustic phonons, and piezo‐acoustic modes are considered. Screening by free electrons is included in the long‐range interactions and shown to play an important role at higher electron concentrations. Both spin‐conserving and spin‐flip transitions are considered for all modes. It is demonstrated that transverse branches participate appreciably in acoustic scattering at high electron energies. In all cases, the presented calculations give much higher values of the theoretical mobilities for heavily doped samples than those obtained up to now taking into account only the proper density of states.
Magnetic Pinch in n‐InSb
Authors: Holter Ø.
Published: July 2007

Equations governing the magnetic pinch in semiconductors are derived taking into account the exclusion principle for high plasma densities. The equations represent two non‐linear coupled integral equations, which have to be solved numerically. The plasma distribution, the density on the axis, the self‐magnetic field, and the current‐voltage characteristic are calculated for a specified n‐InSb sample. The axial plasma density is shown to be larger than the thermal density of the crystal at the melting temperature, suggesting a minor role for thermal carrier generation in a fully pinched semiconductor plasma.
Anisotropie in kubischen Supraleitern
Authors: Obst B.
Published: July 2007

Mit der von Träuble und Essmann entwickelten Dekorationstechnik wurden magnetische Strukturen in kubischen Supraleitern untersucht. Im Zwischenzustand zeigt Blei bevorzugte Orientierungen der Phasengrenzen in bestimmten Richtungen. Die Anisotropieerscheinungen werden in Blei‐Thallium‐Legierungen als Funktion des Ginzburg‐Landau‐Parameters x verfolgt. Die beobachtete Anisotropie der spezifischen Grenzflächenenergie σNM läßt sich im Rahmen der phänomenologischen Theorie von Ginzburg und Landau nicht verstehen. Versuchsweise werden in das σNM‐Funktional für den isotropen Fall die mikroskopischen Größen eingesetzt und die Anisotropie allein durch den Parameter der Energielücke Δ beschrieben. Die sich so ergebende Orientierungsabhängigkeit von Δ wird mit theoretischen Vorhersagen verglichen.
Absorption and Fluorescence Spectra of Tm3+ in YVO4 and YPO4
Authors: Knoll K. D.
Published: July 2007

The optical absorption spectra of trivalent thulium in single crystals of YVO4 and YPO4 were measured in the range from 5000 to 29000 cm−1 including the Zeeman effect at 85, 4.2, and 2K. Furthermore the fluorescence spectrum in YVO4 between 19000 and 25000 cm−1 was investigated. Some special features of the spectra can be explained by the assumption that in several cases the crystal field eigenfunctions consist essentially of one free ion Ψγ J M. From the splitting of Tm3+ in YVO4 values for the crystal field parameters were determined.
Channel Conductivity of Cleaved and Annealed Germanium Surfaces
Authors: Wienskowski J. V. , Mönch W.
Published: July 2007

The channel conductivity of clean germanium surfaces cleaved in ultrahigh vacuum has been measured for 10 Ωcm n‐type bulk resistivity. Immediately after cleavage the surface conductivity is found to be 2.8 × 10−4 Ω−1 ± 50%. The corresponding surface potential is evaluated to (EF − Ei)s = −(0.387 ± 0.04) eV, i.e. the valence band edge coincides with the Fermi level at the surface. A lower limit of the surface state density is estimated to 1 × 1013 cm−2. Upon annealing the cleaved surface at 420°K the surface conductivity decreases by about 70%. The surface potential is thus lowered to (EF − Ei)s = −(0.292 ± 0.05) eV. The surface state density then amounts at least to 2 × 1012 cm−2.
Galvanomagnetic Coefficients for p‐Type Lead Telluride
Authors: Gupta S. C. , Sreedhar A. K.
Published: July 2007

The longitudinal and transverse components of the magnetoconductivity tensor have been calculated for degenerate p‐type lead telluride for the parabolic and non‐parabolic, non‐ellipsoidal band models. The results obtained on the basis of these two models are compared for acoustic, optical, and impurity scattering mechanisms assuming a scalar isotropic relaxation time. It is shown that the importance of acoustic scattering increases relative to optical scattering when the bands become non‐parabolic and energy surfaces non‐ellipsoidal.
Spin Fluctuations in Co0.5Zn0.5Fe2O4 Using the Mössbauer Effect
Authors: Iyengar P. K. , Bhargava S. C.
Published: July 2007

Mössbauer measurements in Co0.5Zn0.5Fe2O4 with 14.4 keV γ‐rays from Fe57 are reported. The spectra, in the temperature range from 90 to 455 °K, show features characteristic of relaxation effects. The shape of the spectra is related to the dynamical properties of the spins using a stochastic model for spin fluctuations. The overall agreement of the experimental data with computed shapes is satisfactory. There is no significant change in the value of relaxation time in the temperature range between 90 and 387 °K, and the change in the shape of the spectrum is mainly due to an increase in the value of s (the spin population parameter), and a decrease in the value of δ. A significant difference in the transition temperatures, as determined by neutron diffraction and the Mössbauer effect, can be explained to be due to the effect of relaxation on the shape of the Mössbauer spectrum. The presence of the relaxation effect is attributed to the influence of Zn2+ ions.
Lifetimes of Parity Forbidden Transitions of the Cu+ Center in the Alkali Iodides
Authors: Mack S. A. , van Sciver W. J.
Published: July 2007

The ultraviolet photoluminescence spectra and excited state lifetime measurements of the Cu+ center in the alkali iodides are reported from 5 to 300 °K. The long lifetimes (greater than 10 μs for all temperatures) obtained indicate that a forbidden transition is involved. The strong temperature dependence of the emission lifetime for LiI:Cu and NaI:Cu is explained on the basis of a linear electron–phonon interaction coupling even and odd parity states, whereas the weak temperature dependence and shorter lifetimes observed for KI:Cu and RbI:Cu are explained on the basis of an off‐center position for the Cu+ excited ion. The oscillator strength determination for the Cu+ absorption in RbI:Cu and the temperature dependence of the absorption for LiI:Cu are reported. These measurements and similar measurements by other authors on NaI:Cu and KI:Cu are compared with the lifetime data. The absence of a correlation between lifetime and absorption measurements indicates that the levels involved in the emission process are different from those of the absorption process.
Parelektrische Resonanz von Li+ in KCl Messungen im E‐Band und Unter Einachsigem Druck
Authors: Blumenstock D. , Osswald R. , Wolf H. C.
Published: July 2007

Parelektrische Resonanz (PER) an Li+ in KCl wurde bei verschiedenen Frequenzen zwischen 60 und 75 GHz, sowie unter einachsigem Druck bei 35 GHz beobachtet. Die Messungen wurden für drei Orientierungen des statischen elektrischen Feldes Eo und des Drucks P bezüglich der Kristallachsen durchgeführt. Sie stützen das kürzlich [1] vorgeschlagene Modell und können mit folgenden Parametern erklärt werden: Das elektrische Dipolmoment |P| = (6,0 ± 0,3) Debye zeigt in eine [111]‐Richtung. Eine Tunnelbewegung des Li+ ist längs der [100] und der [110]‐Achsen möglich.Die zugehörigen Matrixelemente sind: |K| = (11,6 ± 0,2) GHz und |F| = (3,2 ± 0,2) GHz. Für die Differenz der Hauptwerte des elastischen Dipoltensors ergibt sich: λ1 – λ2 = (6 ± 2) × 10−3.
Quantum Statistics of Ionization and Shielding Effects in Non‐Degenerate Moderately Doped Semiconductors
Authors: Ebeling W.
Published: July 2007

In the framework of the hydrogen plasma model the semiconductor is considered as a system of donors and electrons in a uniform medium. A recently developed quantum‐statistical theory of hydrogen plasmas in thermal equilibrium is applied to this simple model; the lowering of the activation energy is calculated exactly up to the order O(n) where n is the electron density. Especially the influence of shielding effects on the activation energy is studied. A method for the treatment of partly compensated semiconductors is proposed. Explicit results are given for the degree of ionization in n‐type Ge as a function of the donor concentration and the temperatures. The limits of the stability region with respect to ambipolar diffusion are diseussed.
Phonon Structure in the Luminescence of Sm++ Doped KClxBr1–x and KxRb1–x alloys
Authors: Baldini G. , Guzzi M.
Published: July 2007

Sm++ ions diluted in alkali halide alloys are employed in order to determine the crystal phonon density of states at low temperature and to probe the degree of configurational disorder in the matrices.
New Type of Ferroelectric Soft Mode in Gadolinium Molybdate
Authors: Petzelt J. , Dvořák V.
Published: July 2007

A group analysis is made of external lattice vibrations in Gd2(MoO4)3 for k = (1, 1, 0) in the high‐symmetry D phase and for the Γ‐point in the low‐symmetry C phase. It is shown that the phase transition is induced by an instability of one double degenerate T1‐phonon at the M‐point of the Brillouin zone which changes into two A1‐phonons, infrared and Raman active below the phase transition. The far‐infrared reflectivity and transmission measurements show that these critical modes are extremely weak and lie at 45 and 56 cm−1 at −150 °C. When rising the temperature they become indistinct and probably disappear above the phase transition. This behaviour together with known dielectric and Raman scattering experiments is discussed in terms of the recent theory of the soft‐mode behaviour in improper ferroelectrics.
Impurity Acousto‐Electric Effect
Authors: Kalashnikov S. G. , Morozov A. I. , Fedosov V. I.
Published: July 2007

The acousto‐electric effect (AEE) and the electronic sound absorption in piezoelectric crystals containing traps are considered taking into account the electron‐sound wave interaction due to the change of the trap ionization energy with deformation. In the AEE additional odd and even components appear besides the conventional Weinreich voltage being proportional to the square of the piezoelectric modulus. The odd component depends on the deformation potentials, the even one (which does not change its sign when inverting the direction of the wave propagation) is proportional to the product of the piezoelectric modulus and the deformation potentials. The even voltage component may be of the same order of magnitude as the conventional odd one provided the traps are not too deep and are present in sufficient concentration. Results of the calculation are compared to experimental data on AEE in ZnS crystals. The combined interaction considered is shown to be the possible cause of the even AEE observed in these crystals.
Non‐Ohmic Electrical Conduction of Semiconducting Thin Films
Authors: Ilkovič V.
Published: July 2007

The effective temperature of conduction electrons, Te, and the parameter β in a thin film of a non‐degenerate semiconductor are calculated taking the quantization of the transverse motion of the electrons into account. These quantities are calculated for mixed scattering by acoustic modes inside the thin film and by surface lattice vibrations.
Electron States of Disordered Systems
Authors: Bhattacharya A. K. , Roy C. L.
Published: July 2007

The integrated density fo electronic states, g(E), of three‐dimensional disordered systems with spherical‐well type of atomic potential is computed. A pertubational treatment (based on Klauder's approach) and a non‐perturbational semiclassical method (based on Bonch‐Bruevich's treatment) have been used for the purpose; two approximate procedures being used for evaluating the dressed electron propagator relevant to the perturbational treatment. Various features of the results of the two treatments are compared and discussed critically. In particular, it is observed that the semiclassical treatment yields a tailing o g(E) extending up to arbitrarily low energies and both the treatments show an overal decrease of g(E) with concentration.
Hot Electron Shubnikov‐de Haas effect in n‐GaSb
Authors: Kahlert H. , Bauer G.
Published: July 2007

The effect of an electric field on the amplitudes of the Shubnikov‐de Haas (SdH) oscillations of Te‐doped n‐type gallium antimonide has been studied in samples with Fermi energies well below the 〈111〉 satellite minima. Therefore the transport effects were due to carriers in the Γ1‐minimum alone. From the decrease of the SdH‐amplitudes the variation of the electron temperature with electric field up to 15 V/cm has been calculated. The measured energy loss rate of the electrons to the lattice is compared with calculated values assuming scattering of the electrons by acoustic phonons. With a deformation potential constant of Ec = 5 eV the deformation potential scattering gives good agreement with the experimental data between 4.2 and 10 K. Above 10 K another unknown energy loss process becomes effective. A two‐phonon mechanism is proposed to explain the observed increase of the energy loss.
Temperature Dependence of the Mn4+ R‐Lines and Vibronic Transitions in MgTiO3 and Mg2TiO4
Authors: Louat R. , Louat A. , Duval E.
Published: July 2007

The vibrational sidebands observed in the fluorescence spectrum of Mn4+ incorporated in magnesium titanates are studied. The salient features of the vibronic spectra are the existence of a resonant mode with a „hot line”︁ in MgTiO3:Mn4+ and the presence of very low energy vibrations in Mg2TiO4:Mn4+. The positions of the R1 fluorescence lines have been measured from 4.2 up to 250 °K. A significant thermal shift is observed and can be interpreted by the presence of linear and quadratic terms in the electron phonon interaction. An effective phonon distribution can be obtained from the vibronic sidebands. The vibrational energy of the lattice is calculated from this distribution and related to the thermal shift.
Experiments on the Zero‐Field Splitting of Trivalent Gadolinium
Authors: Urban W.
Published: July 2007

The zero‐field resonance frequencies of Gd3+ and their dependence on temperature and hydrostatic pressure have been measured on a set of nine isomorphic crystals having the zircon structure. It is shown that the volume effect on the quadrupole term b is much smaller than that produced by the change in local anisotropy of the gadolinium ion. The variety of data obtained fits qualitatively into this interpretation in terms of the dominating role of the quadrupole term. A qualitative microscopic model is suggested correlating the unit cell dimensions to the local anisotropy of the central ion.
High Frequency Conductivity of Polar Semiconductors
Authors: Kranzer D.
Published: July 2007

The ac conductivity is calculated taking into account combined scattering by polar optical modes and ionized impurities. For small electric fields oscillating in time the Boltz‐mann equation is solved. Good agreement between Drude's simple theory and our calculation is obtained in the low‐frequency range whereas the deviation in the high‐frequency range is appreciable.
Determination of Optical Constants: Interband Transitions in Amorphous Ge, Si, and Se
Authors: Jungk G.
Published: July 2007

Ellipsometric measurements are made of the optical constants of amorphous Ge, Si, and Se in the range of interband transitions between 2.0 and 4.0 eV. The results are discussed within the non‐direct transition model. For Ge and Se the discussion indicates transition between flat regions of the initial and final states with energy gaps of ≈ 1.35 and ≈ 2.0 eV, respectively. For Si the density of states behaves like some power of energy with a gap ≈ 1.45 eV. To explain the optical constants at photon energies > 3.0 eV energy dependent densities of states and/or matrix elements must be taken into account for all the three amorphous materials.
Paramagnetic Relaxation and Resonance in Neodymium Ethyl Sulfate
Authors: Kalbfleisch H. , Smolne W. , Thomä R. , Wehrle H.
Published: July 2007

Using two different measuring methods the temperature, magnetic field, and angular dependence of the spin‐lattice relaxation time were studied in neodymium ethyl sulfate crystals with natural isotopic abundance of Nd ions and crystals enriched with the isotope 142Nd. A bottlenecked direct process was found in the low‐temperature range and a Raman process T. ∼ T9 near 4.2 K. The magnetic field dependence is T ∼ H4 only in the field range above 5 kOe. Cross relaxations in the hyperfine structure and via Ce impurities mask the spin‐lattice relaxation.
Optical Absorption by the Cu+ Center in NaI
Authors: Bateman R. L. , van Sciver W. J.
Published: July 2007

The color center which exhibits absorption in NaI at 4.84 eV and emission at 3.30 eV when measured at liquid nitrogen temperature is found to be the Cu+ impurity center. The oscillator strength is determined by performing copper analysis on the same crystals which were measured optically. The value is found to be 0.24 ± 0.03 and to have a weak temperature dependence. The selection of the free ion transition responsible for the absorption is discussed with relation to the oscillator strength and its temperature dependence, the free ion energies of candidate transitions, and ionic size. It is felt that evidence for a choice between the allowed 3d10 → 3d94p and the parity forbidden 3d10 → 3d94s free ion transition is inconclusive at this time.
Influence of magnetic field on conductivity due to electron tunneling between localized states
Authors: Sosnowski L. , Zaręba A.
Published: July 2007

The electrical conductivity due to tunneling of electrons between narrow localized states called transfer states is discussed. It is shown that owing to spin–orbit coupling the magnetic field influences the transition probabilities between the transfer states. A formula for the magnetoconductivity is given and compared with experimental data obtained for an “anomalous” magnetoconductivity in boron.
Photocurrent saturation in CdS single crystals under electron beam excitation
Authors: Picht W. , Ruppel W.
Published: July 2007

The photocurrent generated by 35 keV electrons in CdS crystals shows a more or less pronounced saturation (depending on the thickness of the sample) as a function of the generation rate. A recombination model is described that includes recombination via centres and through exciton states. Further, diffusion into crystal regions primarily not excited is considered. The model accounts for the steady‐state saturation of the current and luminescent emission, for the observed response times as well as the slight additional absorption in the infrared under electron excitation.
Magnetic properties and the structure of impurities in simple metals
Authors: Flynn C. P. , Howe R. A. , Peters J. J.
Published: July 2007

The Knight shifts and susceptibility changes caused by additions of Cu, Zn, Ga, Ge, Ag, and Si to liquid Al are reported, together with the susceptibilities of the pure liquids Zn, Ga, Ge, and As. The data are compared with models of impurity structure in simple‐metal solvents.
Interprétation des structures magnétiques des composés TNi3 à l'aide du champ cristallin
Authors: Rossat‐Mignod J. , Yakinthos J.
Published: July 2007

L'étude par diffraction neutronique des composés TNi3 a montré que les ions terres rares (T) possèdent une anisotropie importante. Par un calcul de champ cristallin d'après la méthode des charges ponctuelles, on interprète qualitativement la colinéarité et la non colinéarité des structures magnétiques. On met en évidence que l'anisotropie due au champ cristallin est très différente pour les deux sites de cette structure complexe.
Dispersion and relaxation in the stress‐induced birefringence of amorphous selenium
Authors: Yu P. Y. , Cardona M.
Published: July 2007

The stress‐induced birefringence (or piezobirefringence) of amorphous Se has been measured at room temperature for wavelengths between 1.15 and 0.77 μm. A ‘bond model’ is proposed to explain the long‐wavelength photoelastic properties of this material. The dispersion in the piezobirefringence was fitted to the two‐parameter phenomenological expression of Wemple and DiDomenico. The relaxation of the piezobirefringence under constant stress, and the recovery of the isotropy after return to zero stress have also been measured at room temperature. From the relaxation curves the birefringence relaxation time for the last Maxwellian element has been determined.
A new model of superconductivity
Authors: Lalović D. I. , Tošić B. S. , Žakula R. B. , Škrinjar M. J.
Published: July 2007

On the basis of a proposed model a new condition for the occurrence of superconductivity is obtained. According to this condition there exists the possibility of high‐temperature superconductivity.
The plasma spectrum effect on acoustic wave amplification by carrier drift in semiconductors
Authors: Kornyushin Yu. V.
Published: July 2007

The effect of plasma oscillations on acoustic wave amplification by carrier drift in semiconductors is discussed. A continuum theory is developed on the basis of hydrodynamical equations for the conduction electrons, the equations for the elastic vibrations of the crystal, and the Poisson equation. It is shown that if the plasma frequency ωp0 is much lower than the reciprocal value of the electron relaxation time for the scattering on phonons and impurities, τ−1, the results are in agreement with available calculations based on the equation for electrical conductivity and diffusion. However, in the case ωp0 τ ≫ 1 the amplification factor is multiplied by 2 ωpτ compared to the value predicted by those calculations, while the optimum drift velocity in this case is ωpτ times smaller.
Etude expérimentale de l'absorption des électrons dans l'or
Authors: Renard D. , Croce P. , Gandais M. , Sauvin M.
Published: July 2007

Des profils de contours d'extinction correspondant à l'image électronique de cristaux d'or courbes d'épaisseur uniforme connue avec précision de 2%, sont obtenus par des mesures directes d'intensité. Des calculs de théorie dynamique à n ondes traitant la partie imaginaire du potentiel cristallin suivant une méthode de perturbation sont utilisés pour déduire des mesures les composantes de Fourier V′g du potentiel imaginaire. Cette méthode permet de déterminer les composantes V′000, V440 avec une précision d'environ 10%. Les résultats sont comparés aux valeurs théoriques données dans la littérature.
Wigner‐Seitz approximation for the description of the mixed state of type II superconductors
Authors: Ihle D.
Published: July 2007

The mixed state of type II superconductors is treated by means of the Wigner‐Seitz approximation in the limit χ ≫ 1 and Hc1 < Ha ≪ Hc2. Expressions for the magnetic field, supercurrent, magnetic induction, and lattice sums are derived. In order to test the accuracy of the Wigner‐Seitz approximation the obtained results are compared with those derived by Fetter et al., good agreement being found.
Paramagnetic orbital susceptibilities of transition metals
Authors: Place C. M. , Rhodes P.
Published: July 2007

The results of numerical calculations of the paramagnetic contribution, χ, to the magnetic susceptibility associated with the orbital motion of electrons in unhybridized tightly bound d‐bands are presented. These results are used to determine approximately the dependence of χ on the number of electrons in the band and on the d‐band width, and to estimate χ. for a number of transition metals. The results obtained are in good agreement with estimates obtained from experimental data. The effect of conduction band‐d‐band hybridization on χ is also considered.
Behaviour of the zero‐field splitting of Gd3+ at low temperatures
Authors: Koch V.
Published: July 2007

The temperature dependence of crystal field splitting for Gd3+ in YVO4, LuVO4, and ScVO4 has been determined from variable frequency EPR. The crystal field parameters of the corresponding spin Hamiltonian were calculated. The temperature dependence of these parameters was fitted with the hyperbolic cotangent. It is shown that an interpretation of the experimental data obtained for YVO4, LuVO4, and ScVO4 in the sense of a dynamic model as proposed by Pfister et al. [1] is not possible. A different interpretation in terms of the anisotropic thermal expansion is suggested.
Ferromagnetic resonance in ruthenium‐doped yttrium–iron garnet
Authors: Hansen P.
Published: July 2007

The ferromagnetic‐resonance field and the linewidth of ruthenium‐doped yttrium‐iron garnet (YIG) have been studied at 9.25 GHz in the temperature range 4.2 to 300°K. The behaviour of the resonance field can be well explained with the single‐ion model which yields the ratio of trigonal field to spin‐orbit coupling ν/ξ = −0.6 and the g‐factor times the exchange field gHe = 1.04 × 107 Oe. The linewidth can be qualitatively interpreted in terms of the longitudinal relaxation model, which requires a very short relaxation time of about 10−13 s.
Energy band calculations for a perfect crystal and a crystal with impurities using a nonlocal potential model
Authors: Fock H.
Published: July 2007

The local potential at each lattice site is replaced by a nonlocal projection operator. Then the eigenfunctions of the electrons can simply be canceled out from the Schrödinger equation. The method of Green's functions is utilized and the calculation of the energy band is restricted to a simple cubic lattice and s‐symmetrical potential function. Energy levels for point impurities and energy bands for one‐ and two‐dimensional impurities are obtained within the band gap or under the valence band. This depends on the depth and the range of the perturbing potential.
Optical activity of ferroelectric dicalcium strontium propionate
Authors: Kobayashi J. , Bouillot J. , Kinoshita K.
Published: July 2007

Optical rotatory power of Ca2Sr(C2H5CO2)6 was accurately measured over a wide temperature range containing both paraelectric and ferroelectric states. The gyration tensor g33 has been determined from the experimental data; for instance, g33 = 2.131 × 10−5, paraelectric at 20 °C, and 2.129 × 10−5, ferroelectric at −20 °C (λ = 546 nm). A theory of optical activity based upon Born's theory has been developed in order to apply it to the ferroelectricity. In the light of the theory the ferroelectric property of Ca2Sr(C2H5CO2)6 is discussed, and it has been revealed that some change occurs around −64 °C in either antisymmetrical parts of interelectronic coupling tensor or shifts of the atoms responsible for its ferroelectricity.
The spin–lattice relaxation in the metal–hydrogen systems on the basis of transition metals of the IVb subgroup
Authors: Khodosov E. F. , Shepilov N. A.
Published: July 2007

The spin‐lattice relaxation times in the systems Ti–H, Zr–H, and Hf‐H were measured by the spin‐echo method as functions of temperature and hydrogen concentration. The theoretical values of T1 min. were calculated in the temperature range where ω τc = 1.4. Comparison of the theoretical and experimental values T1 min. allowed to appreciate the translational diffusion contribution and the possible electronic contribution in the spin‐lattice relaxation. The parametres of the hydrogen self‐diffusion were found. The results are in satisfactory agreement with theoretical concepts developed by Bloembergen et al. [1] and Torrey [2, 3].
Temperature dependence of the absorption edge of amorphous germanium
Authors: Závěctová M. , Voríček V.
Published: July 2007

The measurements of the optical absorption on the three types of amorphous germanium (cathode sputtered. electrolyticelly deposited, and thermally evaporated) in the spectral range 0.5 to 1.5 eV at room and liquid nitrogen temperatures are reported. From the energy dependence of the absorption and its temperature shift we conclude that the corresponding mechanism is based on transitions between the tails in the forbidden gap at lower energies followed by non‐direct transitions at higher ones.
Hall scattering constant in n‐type silicon
Authors: Retmann P. L. , Walton A. K.
Published: July 2007

The factor relating the Hall coefficient to carrier concentration has been determined in n‐type silicon by combining optical measurements of the carrier concentration at infrared frequencies with conventional dc Hall effect measurements. Interpreting this factor in terms of electronic charge, mobility anisotropy and the usual scattering constant, the latter is found to reach values much greater than unity, especially at 77 °K, when with a doping level of 2.6 × 1017 cm−3 a value of 7.3 is obtained.
Piezoresistivity of trigonal SexTe1−x single crystals
Authors: Fuhs W.
Published: July 2007

The longitudinal change of resistivity, Δϱ/ϱ, by uniaxial elastic deformation parallel to the e‐axis was investigated for trigonal Sex, Te1−x single crystals as a function of temperature. The piezoresistivity, π33 = 1/Z3, (Δϱ3/ϱ3), is negative and independent of temperature in the extrinsic Conduction region of tellurium and tellurium‐rich mixed crystals. Another behaviour is found for the selenium‐rich mixed crystals where particularly at low temperature π33 has positive values which are the larger the higher the selenium content is. For pure selenium finally π35 is positive in the whole temperature range investigated and increases appreciably with decreasing temperature. The positive effect is strongly diminished both by illumination of the samples and by an enhancement of the applied voltage. The results show that the positive piezoresistivity is closely connected with the height of the internal potential barriers which control the conduction mechanism of selenium and selenium‐rich mixed crystals.
Optical absorption of Bi+++, Hg0, and Cd0 centres
Authors: Zu Siederdissen J. Höner , Fischer F.
Published: July 2007

For a systematic study of the isoelectronic series of s2‐type centres the absorption bands of some missing centres are measured. Thin layers of alkali halides doped with monodisperse Hg0 or Cd0 are formed by quenching condensation. Single crystals of alkali halides are doped with Bi+++′. In addition of the common bands of s2‐type spectra Bi+++ shows a strong D′‐band. In the isoelectronic series — like Au−, Hg0, TI+, Pb++, Bi+++ — the difference in excitation energies between centre and free ion is nearly proportional to the ionic charge.
Magnetic susceptibility of heavily doped semiconductors in a weak magnetic field
Authors: van Cong H. , Mesnard G.
Published: July 2007

By Green function methods applied to disordered systems, the magnetic susceptibility of heavily doped semiconductors in a weak magnetic field is investigated. A simplified model is used in which the impurity potential is an attractive screened Coulomb potential and quantum exchange‐correlation effects can be neglected. Two important cases arc discussed with the present model. In the first one, we consider an ordinary n‐type semiconductor, assuming that the carrier concentration is equal to the donor one; in the second case, the carrier concentration rises as the cube root of the total concentration of impurities.
Photographic study of the zeeman effect in the satellite structure of praseodymium double nitrates
Authors: Douglas I. N.
Published: July 2007

Satellites associated with the praseodymium transitions in thc spectra of solid solutions of manganese and zinc double nitrates, Pr2Mn3‐xZnx(NO3)12 · 24 H2O, have been observed, and their behaviour in an axial magnetic field has been investigated photographically at 4.2 °K. These satellites are explained in terms of the crystal field perturbation due to an impurity bivalent ion, and parameters describing this effect are derived.
The exciton model of spin and optical excitations of an antiferrodielectric
Authors: Petrov E. G.
Published: July 2007

The spin and optical (electronic) excitations of an antiferrodielectric (AFD) are considered within the framcwork of the exciton model. The most general case of a noncollinear orientation of the AFD sublattice spins is invcstigated. Similarities and differences of the exciton and Heisenberg models of the AFD spin excitations arc shown and expressions are derived for the interaction energy of the electronic and spin excitations of AFD.
Tunnelling results on In‐SrTiO3 barriers interpreted as confirmation of the theory of transitions from large to nearly small polarons
Authors: Eagles D. M.
Published: July 2007

An explanation is given for a large discrepancy between effective masses for current carriers in the conduction band of SrTiO3 deduced from tunnelling data of Sroubek and masses determined by other methods. The explanation is based on the results of theoretical work published in 1969, which showed that the carriers in bulk SrTiO3lie just near the mid‐point of a transition between large and nearly small polarons. Changes in coupling with phonons induced by the electric fields in the surface region are assumed to push the polarons almost entirely into the large‐polaron regime, and quantum size effects then act in such a way as to allow only one of the three valleys of the conduction band to be occupied. It is suggested that structure in reverse bias results may be associated with tunnelling to excited mixed polaron states occurring in the theory of polaron transitions.
The elastic energy of a straight dislocation in an infinite anisotropic elastic medium
Authors: Barnett D. M. , Swasger L. A.
Published: July 2007

An expression for the elastic energy per unit length of a straight dislocation in a medium of arbitrary anisotropy is derived in a form which is simply suited for numerical calculations. The expression utilizes laboratory coordinates throughout and, unlike previous analyses, its evaluation does not rely upon solving the roots of a sextic algebraic equation. Numerical results are presented for glide dislocations in three cubic metals of low, intermediate and large anisotropy — niobium: copper, and lithium.