bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Interionic Potentials in II‐VI Chalcogenide Crystals with NaCl Structure
Authors: Jain V. K. , Shanker J. 
Published: July 2007

AbstractAn analysis of interionic potentials in 45 chalcogenide crystals is performed. New values of van der Waals coefficients derived from the variational formulae are used in the present calculations. The Born‐Mayer repulsive interactions between nearest neighbours as well as between next nearest neighbours are treated by considering the repulsive hardness parameter as an ionic property. This eliminates the well‐known assumption in the Born model according to which one takes a common hardness parameter for different pair interactions. Values of cohesive energies, bulk modulus and its pressure derivative are calculated and compared with other investigations.
Optical and Polarized Luminescence Studies on RbI:Pb2+ at Liquid Helium Temperatures
Authors: Sapru S. , Sastry S. B. S. 
Published: July 2007

AbstractOptical absorption, luminescence, and polarized luminescence studies are made on RbI:Pb2+ from 4.7 to 50 K. It is found that the charge compensating vacancy is predominantly in the next‐nearest neighbour sites at these temperatures. The B‐band shows a splitting and the emission under B‐band excitation disappears around 20 K. Possible crossing of 3T2u and 3Eu levels with 1A1g is suggested to explain the behaviour.
Density of States in Multilayer Sandwiches
Authors: Dubovskii L. B. 
Published: July 2007

AbstractThe density of states of finite metal—semimetal system is considered in the case of boundary conditions that assure the damping of electronic states at infinity. The density of states of the transition region metal‐semimetal is investigated which is found to be strongly dependent on the shape of the transition layer. Special attention is paid to the case when in one part of the system, in the metal, the coherence of the motion of the electron is broken, while in the other part, in the semimetal, the electron moves coherently. Under this condition, the oscillations of the density of states of systems consisting of a metallic film covered on both sides with the semimetal, and systems consisting of two metallic films with a semimetallic interlayer are considered. Within the model described, one can understand the experimentally observed behaviour of Tc (the temperature of the superconducting transition) at small thicknesses of the semimetallic layer.
Infrared and Raman Spectra of Germanium Dichalcogenides I. GeS2
Authors: Popović Z. V. , Stolz H. J. 
Published: July 2007

AbstractThe polarized IR reflectivity and transmission spectra as well as the polarized Raman spectra of single crystalline GeS2 are measured. From a comparison with a factor group analysis most of the expected 141 optically active phonons are identified with their symmetry type. From the observation of rigid layer modes and from the Davydov splitting a force constant anisotropy of about 100 between interlayer and intralayer forces is deduced.
The Mn2+ Ion Spectra in PbxSn1−xTe Alloys
Authors: Hejwowski T. , Subotowicz M. 
Published: July 2007

AbstractElectron paramagnetic resonance (EPR) and Hall coefficient are measured for Mn2+ ‐doped PbxSn1−xTe alloys at temperatures of 77 and 300 K. A rapid change in the HFS constant A and the g‐factor is observed in the range 0.9 ≦ x < 1. In addition, some results for Mn2+‐doped PbTe alloys are presented to confirm the hypothesis of the inhomogeneous distribution of the atoms (Mn, Sn, Pb) in the alloys investigated.
Lattice Dynamics and Some Related Thermal Properties of Body‐Centred Cubic Metals
Authors: Ramji Rao R. , Rajput A. 
Published: July 2007

AbstractA phenomenological model is developed for the calculation of the lattice dynamics and thermal expansion of a homogeneously strained body‐centered cubic (b.c.c.) crystal in which both two‐and three‐body interactions are assumed to operate. The phonon dispersion curves and lattice heat capacity of the four alkali metals Li, Na, K, and Rb, and of the three transition metals α‐Fe, Mo, and W are computed employing four second order parameters in each case. The second‐order elastic constants of these metals are also evaluated. The model is then applied to the four alkali metals to calculate their generalised Grüneisen parameters for various normal mode frequencies and hence the temperature dependence of their effective Grüneisen functions. The results of calculations are in good agreement with the corresponding experimental data wherever the latter exist.
A New Method for Detecting the Wannier‐Stark Ladder in a Semiconductor in a Strong Electric Field
Authors: Berezhkovskii A. M. , Ovchinnikov A. A. , Suris R. A. 
Published: July 2007

AbstractA new method for detecting the Wannier‐Stark ladder in a semiconductor in a strong electric field is proposed. The method is based on the measurement of the interband absorption coefficient in strong parallel magnetic and electric fields at frequencies less than the energy gap.
Order Parameter Symmetry for the β–γ Transition in Pb3(VO4)2
Authors: Hatch D. M. 
Published: July 2007

AbstractThe 100 °C phase transition in Pb3(VO4)2 is theoretically described. The description is in terms of the Landau group theoretical formulation as extended by Birman and Jari°C. Representations from the F point are constructed from which the representation that induces the transition is identified. It is found that this representation satisfies the necessary conditions for a continuous transition. The free energy form consistent with the phase of higher symmetry is constructed as a function of the order parameter and elastic strain.
Infrared Studies of Defects in ZnS Crystals Double‐Doped with Li and Al, Ga, and In
Authors: Król A. , Nazarewicz W. , Gluziński L. , Kozielski M. J. 
Published: July 2007

AbstractInfrared absorption (360 to 500 cm−1) is studied in ZnS crystals doped with both, lithium and a group IIIA dopant. The dominant bands in the obtained absorption spectra can be ascribed to the localized vibrational modes of two types of defects: 1) unassociated Li on a Zn site, Li−Zn, and 2) pairs comprising substitutional Li on a Zn site and substitutional group IIIA impurity on the nearest Zn site, M+Zn‐Li−Zn (M = Al, Ga, or In). Li in ZnS is found to have a considerable effect on atomic interactions in the neighbouring region and, therefore, cannot be regarded as a pure mass defect.
Low‐Temperature Heat Capacities of Pd–Al Alloys at Low Al Contents
Authors: Glugla M. , Severin H. G. , Sicking G. 
Published: July 2007

AbstractThe heat capacities of Pd–Al alloys up to 15 at% Al content were measured in the temperature range between 1.5 and 12 K. The results are discussed in terms of a band‐filling model. In this picture Al admixtures behave like Ag admixtures to Pd but contribute about three electrons to the host instead of one. Conclusions are drawn concerning the superconducting transition temperature in Pd–Al hydrides.
Electrical Conductivity of Superionic AgI between 18 and 26.5 GHz
Authors: Luther G. , Roemer H. 
Published: July 2007

AbstractThe high frequency ionic conductivity σ of the solid electrolyte α‐AgI was measured at temperatures up to 520 K in the microwave K‐band (18 to 26.5 GHz). In contrast to a structure of σ(ω) with a distinct minimum at 20 GHz reported in the literature, a frequency dependence cannot be detected and the same values of σ are measured as are well known from static measurements. The results are in a accordance with a simple “hopping model”.
The Exact Solution of the Curie‐Weiss‐Néel Model Ferrimagnet
Authors: Bowers R. G. 
Published: July 2007

AbstractAn analogue for ferrimagnetism, of the Curie‐Weiss ferromagnet is introduced. The complete thermodynamics of the resulting Curie‐Weiss‐Néel model is obtained. The exact solution of the model is essentially identical with the results of mean‐field theory. Attention is focused on the Néel point and associated critical phenomena. Novel features of critical phenomena in ferrimagnets are considered. Theroretically the staggered magnetization and staggered fields are important whilst experimentally the total magnetization and uniform fields are employed. It is shown that, within the present context, corresponding staggered and uniform properties have identical critical exponents.
The Electron Mobility and Thermoelectric Power in InSb at Atmospheric and Hydrostatic Pressures
Authors: Litwin‐Staszewska E. , Szymańska W. , Piotrzkowski R. 
Published: July 2007

AbstractFirst, theoretical calculations of electron mobility and thermoelectric power in n‐type InSb are reported at liquid nitrogen and room temperatures. All the scattering mechanisms of importance in InSb are taken into account. The calculations based upon a variational solution of the Boltzmann equation are compared with experimental results over the whole available range of electron concentrations. Good agreement between theoretical and experimental results is obtained using the value of deformation potential constant C = 14.6 eV. Secondly, both, experimental and theoretical investigations are made of mobility in InSb under hydrostatic pressure at 77 K within a wide range of electron concentrations. The smallest electron concentrations obtained by freezing the conduction electrons on the metastable states are of order of 1 × 1012 cm−3. Also for those smallest concentration it is possible to describe theoretically the dependence of mobility on the hydrostatic pressure using the same set of parameters as previously, and assuming some compensation of donors by acceptors.
Composition Dependence of the Anisotropy of the Cyclotron Masses in n‐Type Semiconducting Bi1‐xSbx
Authors: Fellmuth B. , Krüger H. , Rudolph R. , Herrmann R. 
Published: July 2007

AbstractThe anisotropy of the band‐edge cyclotron masses of n‐type Bi1‐xSbx (0.07 ≦ x ⪅ 0.16) in the binary plane is determined by investigating the wave propagation in the Voigt configuration B ⟂ C2 ‖ k. At low antimony concentrations (x ≤ 0.10) the anisotropy is independent of x. For x > 0.10 a strong change is observed, where at x ≈ 0.15 a distinct maximum is achieved. These peculiarities can be described by a great variation of the model parameters which determine the energy dispersion in the direction of elongation of the Fermi surface.
Origin of Radiative Transitions from Metastable Minima of the Excited State of Sn2+v−c Centres in Alkali Halides
Authors: Hizhnyakov V. , Soovik T. , Zazubovich S. 
Published: July 2007

AbstractThe dependence of electronic wave functions on the coordinates of not totally symmetric vibrations and the hyperfine interaction are considered theoretically as the possible reasons of the radiative decay of the metastable minima of the sp excited state of Sn2+ vc centres in KCl crystals. It is shown that the dependence of electronic wave functions on the coordinates of not totally symmetric vibrations, which leads to the dynamical lowering of symmetry and removal of forbiddenness for radiative transition from metastable minima (deviation from the Condon approximation), is the main reason of the radiative decay. Taking into account also the mixing of the functions of the radiative and metastable minima by the hyperfine interaction, a 1 to 10% shortening of decay time τ is expected at the transition from natural tin (containing 16% of Sn119) to pure isotop Sn119. A comparison of the decay times is performed which are measured at 2 and 4.2 K for AT luminescence of Sn2+ vc centres in KCl crystals doped with tin having different isotopic abundance. The values of τ in KCl:SnCl2 and KCl:119SnCl2 crystals are shown to differ to about 4%, whereas in KCl crystals doped with the isotope 119Sn the decay time is always shorter than that in KCl with natural tin. This result, being the first experimental observation of the influence of the hyperfine interaction on luminescence decay kinetics of impurity centres in the crystals, is in good agreement with the theory.
Relaxation Time and Effective Masses for Charge Carriers in Semimetallic BiSb Alloys versus Alloy Composition
Authors: Braune W. , Straubel U. , Kubicki N. , Lebech J. , Saermark K. 
Published: July 2007

AbstractRecent investigations on the propagation and damping of magnetoplasma waves in semi‐metallic BiSb alloys allow for the conclusion that the effective masses of the holes and the tilt angle of the electron ellipsoids of the Fermi‐surface do not vary in the semimetallic region of the alloy system. The variations of the effective masses for the electrons with alloy composition can be deduced from magnetoplasma wave data and are in good agreement with cyclotron resonance‐ and quantumoscillation experiments. Observation of the wave damping for different measuring configurations indicates, that the relaxation time for the holes decreases more strongly with increasing Sb‐concentration than the relaxation time for the electrons does.
Adequacy of Local‐Exchange Excitation Hamiltonias in Insulators
Authors: Trickey S. B. , Ray A. K. , Worth J. P. 
Published: July 2007

AbstractThe local‐density (Xα) calculation of insulator band gaps is re‐examined. Both new and extant data show the calculated gaps to be systematically small by substantial percentages (35 to 50%) while cohesive energies, valence band widths, and PV curves are in satisfactory agreement with experiment. The Slater transition state cannot be invoked directly to resolve the dilemma and its periodic generalization is unsuccessful. The simple periodic excitation calculation of ΔESCF can be interpreted usefully in terms of the first exciton absorption, a fact we illustrate in f.c.c. Ar. It is argued that the numerical results indicate strongly that Xα calculations of metal‐insulator transition pressures yield lower bounds to that pressure.
Lattice Sums for Zinc Sulphide Structure Crystals
Authors: Chatterjee S. , Ghosh S. , Basu A. N. 
Published: July 2007

AbstractFollowing the procedure due to Born and his co‐workers a method is developed for evaluating the lattice sums for cubic crystals without a centre of symmetry. For the zinc sulphide structure crystals the like particle sums can be worked out with Born et al. 's formulae but these are not applicable to the unlike particle sums. Further Jacobi's imaginary transformation adopted by Born et al. for the primitive lattices cannot be used in these sums for the evaluation of the integrals. Instead convergence is achieved by the use of Ewald's θ transformation. Finally the explicit formulae for the lattice sums – both, static and periodic – applicable directly to diamond and zinc sulphide structures are deduced.
Electronic Absorption Spectrum of Rb2MnCl4 Single Crystals
Authors: Ghosh B. , Mukherjee R. K. 
Published: July 2007

AbstractThe polarized electronic absorption spectra of Rb2MnCl4 single crystals are studied down to 77 K in the 15 000 to 45 000 cm−1 spectral region. The observed spectral features can be satisfactorily explained by invoking the four‐parameter (B, C, Dq, and α) ligand field model which indicates the octahedral site symmetry around the Mn2+ ion. Two higher energy bands are found to be due to double‐exciton transitions.
Cyclic and dihedral point groups as subgroups of the limiting groups
Authors: Sivardière J. 
Published: July 2007

AbstractIrreducible representations of cyclic and dihedral point groups are deduced from those of the limiting groups ∞ and ∞2. The method is equivalent to that of crystal quantum numbers and gives immediately a classification of spherical harmonics according to the representations of each group. Results are applied to the determination of crystal field splittings and of tensorial invanants and covariants.
A cooperative model of stress relaxation in solids
Authors: Högfors Ch. , Kubát J. , Rigdahl M. 
Published: July 2007

AbstractThe process of stress relaxation in solids is discussed in terms of a two‐level system where stimulated emission of phonons may occur. There is no a priori information on field equations or interaction Hamiltonian but the physically reasonable statistical assumption about the phonon distribution, that they are bosons, is enough in order to describe the macroscopic behaviour qualitatively. With certain approximations, the equation for the stress rate may be solved with analytical methods. Comparison with experiments reveals that this proposed mechanism for stress relaxation might be correct.
X‐ray investigation of thermal expansion and atomic thermal vibrations of tin, indium, and their alloys
Authors: Wołcyrz M. , Kubiak R. , Maciejewski S. 
Published: July 2007

AbstractThermal expansion and anisotropic thermal vibrations are investigated for pure tin, indium, and their intermetallic compounds : In3Sn and InSn4, below and above room temperature. Measurements are performed with spherically shaped single crystals. The dependences of the lattice parameters on temperature are measured by using the high precision Bond‐type diffractometer. Sets of reflection intensities are taken and anisotropic temperature factors were calculated in the structure refinement process. An analysis of the formula concerning the bonding energy of the crystals discussed is carried out. The theoretical thermal expansion coefficients are compared with experimental ones.
Recombination processes in 3 to 5 μm HgCdTe
Authors: Calas J. , Allègre J. , Fau C. 
Published: July 2007

AbstractAn analysis of the decay of the excess majority carriers created by a photon beam with an energy higher than the energy gap is given. The recombination processes as well as the radiative process and also the Auger process are studied for Hg1−xCdxTe when x is nearly equal to 0.30, and their range of validity versus temperature is defined. From the continuity equations, the change of ne versus time is deduced when the recombination takes place in deep levels for a given injectpion rate ne0. The capture cross section NRτn0 of a given level at weak injection rate and at low temperature is obtained from the slope of In(ne(t)). At higher temperature, the population of the re‐ combination level and the ionisation enefgy with respect to the valence band are determined from the slope of ne(t) at high injection rate and from the slope of In(ne(t)) at weak injection.
Excitation induced renormalization effects of the excitonic polariton dispersion in CdS
Authors: Kempf K. , Schmieder G. , Kurtze G. , Klingshirn C. 
Published: July 2007

AbstractThe investigation of the excitonic polariton dispersion curve of highly excited CdS platelets reveals some modifications of the dielectric function ϵ˜(ω, k). Considering the real part of ϵ˜(ω, k), the renormalization effects introduced by an intense laser can be qualitatively described by adding to ϵ˜ appropriate resonance terms. These additional resonances are partly situated at the spectral position of the incident laser, partly their position is correlated to the energy of the biexciton. Furthermore, a weak shift is observed of the excitonic eigenenergy at high excitation. The techniques used to investigate the above‐mentioned anomalies are two‐photon Raman scattering and the study of Fabry‐Perot interferences.
Masse effective des électrons et Eg(x) dans la solution solide CdIn2 (Se1−xTex)4
Authors: Chizhikov V. I. , Panyutin V. L. , Ponedelnikov B. E. , Rozenson A. E. 
Published: July 2007

AbstractPar la méthode du pseudopotentiel empirique, nous avons effecté un calcul de l'évolution de la bande interdite et de la masse effective des électrons en fonction de la composition de la, solution solide CdIn2(Se1−x,Tex)4. L'accord obtenu avec les résultats expérimentaux est satisfaisant.
Study of optical second harmonic generation in ferroelectric liquid crystal
Authors: Vtyurin A. N. , Ermaeov V. P. , Ostrovskii B. I. , Shabanov V. F. 
Published: July 2007

AbstractSecond harmonic generation in the ferroelectric smectic C phase of i‐amyl‐4‐[4‐decyloxybenzylideneamino]‐cinnamate (DOBAMBC) is studied. Its dependences on temperature and external electric field are measured. A considerable effect of orientational fluctuations is pointed out.
Optical measurements of the surface plasmon of copper
Authors: Robusto P. F. , Braunstein R. 
Published: July 2007

AbstractThe optical properties of the noble metal copper are determined by computer fitting the experimentally obtained attenuated total internal reflection (ATR) spectra of its surface plasmon in the visible spectral region (0.42 to 0.63 μm). The dispersion curves of the surface plasmon resonance of copper are determined; they show that the resonance exists on the steep absorption edge of ϵ2 at 2.16 eV. This absorption edge, which is due to the d‐band to Fermi level transition, causes the large shift in the location of the surface plasmon excitation from ϵ1(ωs) = −1 to ϵ1(ωs) = −4.7 and causes the true resonance to occur in the complex frequency plane.
Luminescent analysis of an impurity in the near‐surface layer of thermally evaporated silicon
Authors: Safronov L. N. , Aleksandrov L. N. , Lovyagin R. N. 
Published: July 2007

AbstractA low‐temperature (T = 6 K) photoluminescence of surface silicon layers undergoing thermal evaporation in a high vacuum at 1300 to 1350 °C has been studied. It is found that irrespective of the impurity concentration of the initial samples the bands are observed in the luminescence spectra of the surface region of thermally treated plates, which are due to annihilation of excitons bound with: 1) single non‐ionized boron atoms in substitutional positions of the silicon lattice; 2 ) pairs and clusters of substitutional boron atoms in a layer about 1 μm thick. The processes resulting in the formation of a narrow concentration profile of boron atoms near the surface of a silicon plate are discussed. Boron is accumulated due to a considerable difference (by a factor of about 102) between the rates of evaporation of boron and silicon atoms under non‐steady‐state diffusion.
The model of the phase transition in squaric acid
Authors: Schneider V. E. , Tornau E. E. 
Published: July 2007

AbstractA statistical model of phase transition in squaric acid (C4H2O4 and C4D2O4) crystals is proposed. The thermodynamical properties of the transition are investigated by a five‐particle cluster approximation not taking into account the tunneling motion of protons. It is shown that the phase transition in the analysed model can be of both first and second order. A comparison with recent experimental data is carried out.
Band calculation of copper by an interpolation scheme based on recent pseudopotential methods
Authors: Yamada Y. 
Published: July 2007

AbstractThe interpolation scheme for f.c.c. copper, which is based on the empirical or model‐pseudo‐potential method, is formulated without using Slater‐Koster matrix elements. It is based on the fact that the pseudopotential is separable into the local and nonlocal parts. Consequently, in contrast to the previous methods, the parameters in the d‐d matrix elements do not depend upon the crystal structure and their number is small. The present scheme is applicable to other crystal structures. It is devised so as to give the same condition in the expansion of the Bloch function in terms of plane waves over the first Brillouin zone. The calculated band structures are compared with those obtained by other methods.
On the influence of fluctuations on the Peierls transition of the quasi‐one‐dimensional Fröhlich model with a nearly half‐filled band
Authors: Puff H. 
Published: July 2007

AbstractThe influence of fluctuations on the Peierls transition of the quasi‐one‐dimensional Fröhlich model with a nearly half‐filled band is investigated within a renormalized random phase approximation. In the limit of weak interchain coupling, the stability limit of the normal phase with respect to the formation of a commensurate charge‐density wave is calculated.