bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impurity Acousto‐Electric Effect
Authors: Kalashnikov S. G. , Morozov A. I. , Fedosov V. I. 
Published: July 2007

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractEllipsometric 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

AbstractUsing 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractL'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

AbstractThe 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.
The plasma spectrum effect on acoustic wave amplification by carrier drift in semiconductors
Authors: Kornyushin Yu. V. 
Published: July 2007

AbstractThe 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

AbstractDes 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractOptical 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractFor 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

AbstractBy 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

AbstractSatellites 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

AbstractThe 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

AbstractAn 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

AbstractAn 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.