bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Dependence of the Infrared Absorption Spectrum of P4S3
Authors: Chattopadhyay T. , Von Schnering H. G.
Published: July 2007

The temperature dependence of the infrared absorption spectrum of P4S3 is investigated from 10 to 360 K. The internal mode frequencies have negligible temperature dependence whereas the external mode frequencies show a relatively strong temperature dependence which is almost linear. At the phase transition temperature 314 K the sharp absorption peaks due to the low‐frequency external mode disappear leaving relatively flat features characteristic of the plastic phase.
The Crystal Field in the Hexagonal Compound PrCu5
Authors: Andreeff A. , Goremychicin E. A. , Griesswn H. , Kaun L. P. , Lippold B. , Matz W. , Chistyaeov O. D. , Savitskii E. M. , Ivanitskii P. G.
Published: July 2007

Crystal field effects on inelastic neutron scattering, specific heat, and susceptibility are studied in PrCu5. From the neutron scattering experiment the following crystal field parameters are determined: B02 = 0.48 meV, B04 = −8,5 × 10−4 meV, and B06 = 49 × 10−6meV B66 = 14 × 10−4meV. The ground level is a P1 singlet. Using these Bml the specific heat, the susceptibility, and the thermal conductivity of PrCu, are computed and compared with experimental results.
Conversion of F‐HA Pairs into α‐IA Pairs in KBr:Li and KBr:Na X‐Rayed at 80 K
Authors: Dauletbekova A. , Elango A.
Published: July 2007

An optical method is used to investigate the dependence of the number of defects, created by X‐irradiation at 80K (F, α, HA, V4, V4A, and IA, centres), on the impurity concentration in KBr:Li and KBr:Na. It is revealed that the amount of α‐IA pairs in the total anion defect number increases (approximately up to 90%) and the amount of F‐HA pairs decreases with the increase of the impurity concentration. As a reason the tunnel recharge of neutral primary F‐HA pairs into charged α‐IA pairs is considered, the probability of which increases with the decrease of the distance between the partners (i.e. with the enhancement of the impurity concentration).
An Extended Interionic Potential for Alkali Halides
Authors: Murti Y. V. G. S. , Selvarajan T. V.
Published: July 2007

A ten‐parameter interionic potential is developed for the alkali halide crystals of rocksalt structure within the framework of the shell model for ionic crystals. This potential is an extension of the traditional Born‐Meyer form and takes into account the additional coupling between the repulsive overlap force and dispersion force. The analytical form of the proposed short‐range interaction potential is suggested by the coupled Drude oscillator model: Φii(r) = Bii exp (−r/σii) + Aii[(1/σii)2 − 2/σiir] Bii exp (−r/σii) − Cii/r6 for like ion pairs and Φij(r) = Bij exp (−r/σij) for unlike ion pairs. The four like ion parameters (Bii, σii) are determined by recourse to the Thomas‐Fermi electron gas model. The unlike ion repulsion parameters (Bij, σij) are fixed by the requirement of consistency with the equilibrium lattice constant as well as with the dielectric data as in the shell model. The van der Waals coefficients Cii and the coupling parameters Aii are treated to be crystal‐independent. A common set of these parameters is deduced by fitting to the elastic constants over the family of sixteen crystals. The resulting van der Waals coefficients are found to be generally large for both, cations and anions. The effect of input data on the constructed potentials is studied.
Phase Transition and Spatial Correlation of Localized States in the Falicov‐Ramírez‐Kimball Model
Authors: Lazo E. , Röessler J. , Moraga L. A.
Published: July 2007

The Falicov‐Ramirez‐Kimball model is solved by means of the two‐atom cluster Caron‐Pratt approximation. Metallic and insulating phases according to the value of an order parameter Δ are obtained, and both second‐ and first‐order phase transitions between them. Two kinds of insulating solutions (ordinary and mixed valence) and a variety of metallic states with different inter‐ionic degrees of correlation are obtained. These results are found to be inqualitative accord both with experiments and former theoretical treatments.
Dynamics of Two‐Spin Cluster in Spin Glass: I. Simple Model Calculation for Remanent Magnetization
Authors: Nara S. , Freudenhammer A. , Heber G.
Published: July 2007

The dynamics of a two‐spin system in a magnetic field is investigated. This system can be regarded as the most dominant two‐spin clusters in some spin glass in the first approximation of cluster expansion theory. Two Heisenberg spins are considered with one‐ion anisotropy in a magnetic field. The spin quantum number is taken as S1 = S2 = 1. The field may be regarded as the superposition of external field and molecular field created by the other clusters. The result of quantum version is briefly compared with the previous work of classical treatment. Assuming that the two spin clusters are in some metastable state due to frustration effects of spin glass, a possible interpretation of an experimental fact is presented — the field dependance of remanent magnetization, which indicates one common dynamical property for several kinds of spin glasses.
Self‐Trapped Exciton Luminescence after Tunnelling of Vk and Nao Centers in CsI:Na Crystals
Authors: Imanaka K. , Kayal A. ‐H. , Mezger A. C. , Rossel J.
Published: July 2007

Tunnelling recombination luminescence in CsI :Na crystals is studied by means of linear polarization, magnetic circular polarization, and optical detection of ESR either under or after X‐ray irradiation. Results are well interpreted in terms of a self‐trapped exciton (STE) scheme as the final emitting state of tunnelling recombination; here, in the present case with tunnelling, the population for each STE sublevel is derived from the thermal equilibrium spin populations of trapped electrons (NaO) and holes (Vk) instead of the usual creation rate in UV light excitation case.
Simple Spectral Density Approach to the Problem of Mixed Valency
Authors: Nolting W. , Olés A. M.
Published: July 2007

A simple spectral density approach is proposed for the extended Falicov‐Kimball model to describe the phenomenon of mixed valency observed in 4f‐compounds. The general influences of typical model parameters, as for instance the Coulomb interaction g between localized f‐ and itinerant s‐electrons or the s‐f hybridization V, on characteristic properties of intermediate valence compounds are calculated and discussed. Depending on the parameters g and V the theory predicts both first‐and second‐order transitions as found for the Sm chalcogenides.
Critical Anomaly of the Electron Spin‐Lattice Relaxation in X‐Irradiated Rochelle Salt
Authors: Völkel G. , Müller H.‐E. , Flohrer W.
Published: July 2007

Using the electron spin‐echo technique the spin‐lattice relaxation time T1 of a free radical in X‐irradiated Rochelle salt and in the solid solution NaK0.985(NH4)0.015C4H4O6 · 4 H2O are determined in the temperature range from 90 to 300K. In the close vicinity of the upper and lower phase transitions of both crystals a critical behaviour of the longitudinal relaxation can be detected. Several ways of analysing this behaviour are discussed. They all reveal a critical increase of T1. Measurements of crystals irradiated with different X‐ray doses show that the anomaly in T1 is shifted simultaneously with the phase transition temperatures. The observed anomaly is explained by the influence of an increasing phonon damping at the ferroelectric phase transition on the spin‐lattice relaxation time.
On the Luminescence of Sm3+, Gd3+, and Dy3+ in Yttrium Aluminium Borate
Authors: Kellendonk P. , Blasse G.
Published: July 2007

Concentration quenching of the luminescence in Y1−xRExAl3B4O12 (RE = Sm, Gd, Dy;0 < x ≦ 1) is examined. In the case of gadolinium compound the quenching is due to energy migration among the Gd3+ ions to quenching centres. From the decay curve of GdAl3B4O12 a lower limit for the diffusion constant at 300 K is derived. The quenching of the Sm3+ and Dy3+ ion emission can be ascribed to resonant cross‐relaxation. The interaction between the ions is probably of the electric dipole‐dipole type. The critical concentrations for the transfer processes are given.
Effect of Magnetic Field on the Susceptibility and the Specific Heat of Spin Glasses
Authors: Das S. K. , Joshi S. K. , Tripathi R. S.
Published: July 2007

The susceptibility and the specific heat of spin glasses in the presence of an external magnetic field are calculated within the frame of Edwards' and Andersons theory. The quantum Heisenberg Hamiltonian is used with exchange interactions distributed randomly about a positive mean. The field dependence of the susceptibility and the specific heat are compared with the experimental data near the spin glass transition temperature.
Effect of Size Quantization on the Einstein Relation in Ultrathin Films of n‐Cd3As2
Authors: Chakravarti A. N. , Ghatak K. P. , Ghosh K. K. , Ghosh S. , Mukherjee H. M.
Published: July 2007

An attempt is made to investigate the effects of size quantization on the Einstein relation for the diffusivity‐mobility ratio in ultrathin films of n‐Cd3As2. It is found that the ratio increases, at a given electron concentration, with decreasing film thickness and also increases with increasing electron concentration corresponding to a given film thickness. For extremely thin films, the influence of size quantization becomes increasingly prominent with decreasing values of the electron concentration.
Semiempirical Calculations of Defect Properties in LiF Crystal
Authors: Shluger A. L. , Kotomin E. A.
Published: July 2007

To obtain the electronic structure of both, perfect and imperfect ionic crystals the standard calculation scheme of the INDO semiempirical method is modified in order to consider the interaction of valence electrons with ionic cores more accurately than it has been done so far. The INDO parameters are optimized to reproduce a number of experimentally observed properties of a perfect LiF crystal. The parameters derived permit to reproduce quite well the distinctive properties of free F02, F−2, LiF molecules which is necessary for reliable calculations of the properties of intrinsic hole defects.
Evidence of the Conduction–Valence Band Overlap Induced by a Magnetic Field in Zero‐Gap Hg1–xMnxTe
Authors: Sandauer A. M. , Byszewski P.
Published: July 2007

Experimental evidence and theoretical results are given of the conduction–valence bands overlap induced by an exchange interaction in zero‐gap Hg1–xMnxTe. The Fermi level as well as the concentration of electrons and holes strongly depend on the magnetic field in the region where the overlap exists.
The Vibrational Entropy Change Associated with the Disordering of a Two‐Dimensional Binary Alloy Using a Model of Nearest‐ and Next‐Nearest‐Neighbour Interactions
Authors: Bakker H.
Published: July 2007

In a model of harmonic central forces, acting between nearest and next‐nearest neighbours the change of vibrational entropy due to disordering of a completely ordered binary alloy is calculated numerically. The crystal structure is the two‐dimensional square lattice. The temperature is well above the Debye temperature. A comparison is made with results obtained previously using a different model. It turned out that the values of the entropy change are not too much model dependent in the examples investigated. Again it appears that the change of the vibrational entropy is of a similar magnitude as that of the configurational entropy.
On the Susceptibility of the Periodic Anderson Model
Authors: Elk K.
Published: July 2007

The periodic Anderson model is studied as a simple model describing intermediate valence compounds. In this model a strong electron–electron correlation is taken into account. The correlation term is decoupled using the alloy analogy approximation, which yields a two‐peak structure of the density of states of the f‐electrons. Then the isothermal longitudinal susceptibility χ can be obtained by means of the Green function technique. Restricting the effective coherent potential to the atomic limit the temperature dependence of χ is computed. It is found that caused by the strong correlation χ diverges atT→ 0, in contrast to the Pauli behaviour observed experimentally in intermediate valence compounds. On the other hand, the strong dependence of χ on the electron densityncan be explained.
Investigation of Superhyperfine Interactions of Mn2+ in α‐LiIO3 and Evaluation of Lithium Quadrupolar Interactions
Authors: Daraselia D. M. , Bräer A.
Published: July 2007

The models of two types of paramagnetic centres in manganese‐doped LiIO3 are determined by means of the radiofrequency discrete saturation method (RFDS) and ENDOR, which measure the superhyperfine interactions of the centres with the neighbouring 7Li nuclei. Manganese is arranged at lithium sites and charge compensation results from a vacancy at a lithium site. The measured quadrupolar splitting parameters of the 7Li nuclei are calculated with good agreement in point charge approximation on the basis of the models determined.
Kr and Xe Guest Atoms in Ar Matrix: Emission Spectra, Excitation Spectra, and Lifetimes
Authors: Hahn U. , Haensel R. , Schwentner N.
Published: July 2007

Emission bands of isolated Kr and Xe atoms in solid Ar matrices are assigned to atomic 3P1 and 1P1 states on the basis of excitation and emission spectra. The temperature and concentration dependence of these spectra is used to sort out emission from distorted sites. The dependence of the lifetimes on temperature reflects the competition between radiative and nonradiative decay.
Investigation of EPR and Thermoluminescence Glow‐Curves of X‐Irradiated KCl:CrO, Ca2+ Crystals
Authors: Alybakov A. A. , Toichiev N. , Akchalov Sh.
Published: July 2007

KCl crystals doped with CrO and Ca2+ are studied. It is shown that in these crystals there are impurity centres being the complexes CrO with anion vacancy and CrO with Ca2+. As a result of X‐irradiation, the Cr6+ ions in these centres turn into the paramagnetic pentavalent state and show EPR spectra of two types lettered A1 and A2. The A1 spectrum is interpreted as to be due to Cr5+ ions generated in the complexes with anion vacancy; the A2 spectrum is assigned to the Cr+5 ions generated in the complexes with Ca2+. A comparison with the results of thermoluminescence study shows, that heating results in the destruction of paramagnetic centres. A thermoluminescence peak at 436 K corresponds to the A1 centre destruction and a peak at 486 K corresponds to the A2 centre destruction.
Transport Properties of PrNi5 at Low Temperatures
Authors: Reiffers M. , Flachbart K. , Jáoš Š. , Beznosov A. B. , Eska G.
Published: July 2007

The temperature dependence of the electrical resistivity and thermal conductivity of PrNi5 is investigated. In the electrical resistivity at temperature around 10 K a slight anomaly indicating the crystal‐field effect on the resistivity is observed. The thermal conductivity shows a linear temperature dependence in the temperature range 0.5 to 20 K.
Luminescence Accompanying the Recombination of Electrons with VF Centres in KCl Crystals
Authors: Egemberdiev Zh. , Zazubovich S. , Seeman V. , Nagirnyi V.
Published: July 2007

Processes of an optical production of VF centres (holes localized near cation vacancy) are investigated by absorption, ESR, and thermoluminescence methods. It is established that VF centres are most effectively produced in KCl: PbCl,2 crystals X‐irradiated at 80 K and subsequently heated up to 270 K, at the recombination of optically released electrons with V2z(Pb2+) centres (molecular Cl ions associated with Pb2+ ions). After an optical production of VF centres, the stimulation in the electronic absorption bands (K or L2) results in the appearance of luminescence with a peak at 3 eV and band half‐width equal to 0.75 eV. If VF centres are previously oriented by polarized light, the 3 eV emission becomes polarized in the directions perpendicular to the molecular axis of the oriented VF centres. The 3 eV emission quenches rapidly at 237 K and its depolarization occurs at 111 K. The same emission is observed in undoped KCl crystal. It is concluded that the 3 eV emission is caused by the recombination of electrons with VF centres. The same spectrum must have the triplet emission of a self‐trapped exciton perturbed by a cation vacancy.
Electron Paramagnetic Resonance of Gold in Silicon. II. Cluster Centres
Authors: Höhne M.
Published: July 2007

The interpretation of the EPR spectrum suggests two alternative models: five gold atoms or three gold atoms with two boron atoms, respectively, form a cluster occupying lattice sites and adjacent interstitial sites. This cluster tends to further precipitation. Both of the paramagnetic gold‐related centres – that with one gold atom and the cluster – are assumed to belong to the group of acceptor levels in Si:Au.
Optical and Electrical Investigations of the Anisotropy of Sb2Te3 Single Crystals
Authors: Langhammer H. T. , Stordeur M. , Sobotta H. , Riede V.
Published: July 2007

On Sb2Te3 single crystals with conductivities between 3700 and 7000 Ω−1 cm−1 the anisotropy of the reflectivity of polarized infrared light, the anisotropy of conductivity and of the Seebeck and Hall coefficients are investigated. In addition to the excitation of free carriers in the reflection spectra of donor doped crystals also interband excitations are observed. In terms of a six‐valley band model with anisotropic scattering the contribution of the free carriers to the susceptibility is calculated, and the anisotropy ratio of the effective susceptibility masses magnified image is given. It is found that the anisotropy decreases with increasing conductivity. A comparison of magnified image with the anisotropy of conductivity σ ⊥c/σ‖c shows that for Sb2Te3 single crystals with σ‖σ ⊥c < < 5000 Ω−1 cm−1 the carrier scattering is anisotropic.
Theory of Interatomic Forces in Rare Gas Crystals
Authors: Shanker J. , Rajauria A. K.
Published: July 2007

The theory of interatomic forces in rare gas crystals is used to calculate the cohesive energy, the third‐order elastic constants, and the pressure derivatives of the second‐order elastic constants for Ne, Ar, Kr, and Xe. The method of Lehri and Verma based on the three‐body force model is revised. The results obtained are compared with the corresponding values determined by Zucker and Paik from a different model based on long‐range three‐body interaction terms. The cohesive energies calculated in the paper present good agreement with experimental data.
The CNDO/BW Study of Lithium Clusters II. B.C.C. Clusters
Authors: Skála L.
Published: July 2007

The CNDO/BW method is used for a detailed study of b.c.c. lithium clusters. The equilibrium distances between atoms, binding energies, one‐electron energies, charges at atoms, bond orders, and dipole moments are investigated for 13 clusters with 5 to 35 atoms. For greater clusters, an extrapolation of the results is used and discussed.
Nuclear Quadrupole Effect and Phase Transition in the Quasi‐One‐Dimensional Conductor β‐Na0.33 V2O5
Authors: Onoda M. , Takahashi T. , Nagasawa H.
Published: July 2007

The angular dependence of the main NMR resonance lines of the 51V nuclei in β‐Na0.33V2O5 is measured above and below the first‐order structural phase transition temperature in the frequency range between 10 and 20 MHz. The nuclear quadrupole interaction parameters of the broad resonance line are determined, and the principal axes of the electric field gradient tensor are found to coincide with those of the crystalline field around the vanadium atoms in site I.
On the Theory of Longitudinal Magnetoresistance of Metallic Films and Wires
Authors: Kogan E. M. , Ustinov V. V.
Published: July 2007

The quasiclassical kinetic equation for the conduction electrons distribution function and boundary conditions for this equation are written in “action‐angle” variables. It allows to obtain a relation between the boundary condition parameters and the quantum surface collision integral for conduction electrons with an arbitrary dispersion law. The use of the “action‐angle” variables is found to be very convenient for the conductivity calculation in films and wires in a longitudinal magnetic field. With their help general formulas for the longitudinal magnetoresistance both of films and wires with an arbitrary conduction electron dispersion law and an arbitrary surface scattering are obtained.
Calculation of the Electronic Density of States in Disordered Metallic Systems
Authors: Lai S. K. , Wang S.
Published: July 2007

The use of N(E) = NFEk(∂E(k)/∂k)−1 as the electronic density of states for disordered metallic systems is critically examined. The present examination shows that its use is reasonable and that the applicability of the nearly‐free‐electron theory to the binary alloys of simple metals becomes worse and worse in going from the case of small charge transfer to the case of large charge transfer.
Luminescence and Optical Investigation of NaF:Ce3+ Single Crystals
Authors: Bhan S.
Published: July 2007

It is observed that undoped NaF samples exhibit four glow peaks at 73, 120, 143, and 223 °C and NaF doped with Ce3+ samples exhibit an additional peak at 183 °C. The 73 °C peak is attributed to F'‐centres and the remaining peaks to F‐centres. Involvement of Ce3+ impurity is suggested in the origin of the 183 °C peak. Ce3+ impurity does not change its valence state on irradiation. It acts as an activator during luminescent process.
Method of Invariants Applied to Indirect Gap Absorption
Authors: Bednarek S. , Rössler U.
Published: July 2007

The phonon assisted optical transitions at the fundamental (indirect) absorption edge in Si and GaP are described using the invariant method. In contrast to earlier work the spin degeneracy of the electron states is considered. Transitions are found which become allowed due to spin–orbit coupling.
The Impact‐Parameter Dependence of Energy Losses in Proton Scattering by Gold Atoms
Authors: Iferov G. A. , Zhukova Yu. N.
Published: July 2007

The energy losses of protons scattered by atoms of gold are measured in the impact‐parameter range of 0.4 ≦ ϱ/αTF ≦ 4.0 where αTF is the Thomas‐Fermi radius. If the penetration depth of a proton into the electronic shell of an atom increases, there occurs a peculiar saturation of the stopping power at ϱ/αTF ≧ 1 at the levels (0.35 ± 0.05), (0.45 ± 0.05), and (0.52 ± 0.05) keV/ atom for incident beam energies of 100, 200, and 400 keV, respectively.
Third‐Order Elastic Constants and Pressure Derivatives of Second‐Order Elastic Constants of Fluorite‐Structure Crystals
Authors: Shanker J. , Singh J. P.
Published: July 2007

An analysis of interionic potentials is performed in CaF2, SrF2, BaF2, PbF2, Sr(NO3)2, Ba(NO3)2 crystals with fluorite‐structure. Lundqvist's three body interactions and the van der Waals dipole‐dipole interaction along with short‐range overlap repulsive interactions are taken into account in order to evaluate the third order elastic constants and pressure derivatives of second order elastic constants for the crystals under study. The results obtained are compared with those calculated from the shell model and two body potentials and also with experimental values.
Perturbation Expansion for the Asymmetric Anderson Hamiltonian II. General Asymmetry
Authors: Horvatić B. , Zlatic V.
Published: July 2007

The asymmetric single‐orbital Anderson model is studied by the rapidly convergent perturbation method of Yosida and Yamada. Low‐temperature specific heat, resistivity, thermoelectric power, and renormalized position of the virtual bound state are evaluated to the second order in Coulomb correlation for arbitrary asymmetry. The effect of asymmetry on the properties of the model is discussed. It is found that the correlation effects are most pronounced in the case of electron–hole symmetry and are strongly reduced with the increase of asymmetry.
Photosensitive EPR of Ge3+ and Sn3+ in Twinned Cubic Zinc Sulfide
Authors: Backs D. , Freyer H. J.
Published: July 2007

Germanium‐and tin‐doped cubic ZnS single crystals are investigated by EPR and optical excitation and quenching spectra of EPR. In the case of tin‐doped cubic ZnS a different g‐factor is observed than for haxagonal ZnS. The hyperfine intersaction with Sn115 in ZnS is observed for the first time. From the excitation and quenching spectra a simple level scheme is proposed to explain the electornic transitions. Charge exchange is obnserved in the quenching process of Ge‐doped ZnS between germanium and iron, and between tin and chromium for tin‐doped ZnS. From this it is concluded that Ge and Sn are incorporated into the host lattice on cation site and in a divalent charge state.
Exciton and Electron‐‐Hole Liquid Luminescence of Germanium in an Electric Field
Authors: Ganser M. , Seelmann‐Eggebert M. , Huebener R. P.
Published: July 2007

Measurements of the exciton and the electrron–hole liquid (EHL) luminescence of optically pumped germanium are reported for the temperature range of 2.1 to 4.2 K in the presence of an electric field. Simultaneously with the luminescence the electrical conductivity behaviour is studied. At an electric field near 3.0 V/cm the EHL luminescence sharply drops to zero. With increasing field the drop of the free‐exciton luminescence is less sharp than that of the EHL luminescence and sets in as soon as the EHL luminescence vanishes. This field dependence together with the conductivity results can be explained by impact ionization of the free excitons. Apparently during this process the EHL acts as a buffer for the free‐exciton system.
Collective Phenomena in Edge Emission of ZnTe and ZnSe Crystals
Authors: Baltramieyunas R. , Kuokshtis E.
Published: July 2007

The radiative recombination of highly excited ZnTe and ZnSe single crystals in their self‐absorption region is studied. The new L‐ and P‐bands are observed in the emission spectra of the crystals under investigation. It is established on the basis of experimental and theoretical analysis of the spontaneous luminescence and optical gain spectra shapes, their dependence upon the excitation intensity and temperature, as well as shallow impurities, that radiative transitions in electronhole drops (EHD) predominate in luminescence at low temperature (4.2 K) in the most pure ZnTe and ZnSe crystals and are responsible for the L‐band. The P‐band caused by radiative processes in dense partly ionized exciton gas appears in the luminescence spectra in the defective crystals or at high temperature. The question is discussed of the competition of the radiative recombination in EHD and in exciton gas, as well as in homogeneous electron‐hole plasma forming near the surface of the crystal or under the thermal splitting of excitons.
Iteration Method in the Theory of Nonhomogeneous Dielectrics
Authors: Fokin A. G.
Published: July 2007

The problem of finding the relationship between an unknown field E and the field Ec, which is the solution of a similar boundary value problem for an auxiliary medium, is solved for an arbitrary (in the sense of the distribution of the nonhomogeneities and their dielectric properties) nonhomogeneous medium of volume V. The Poisson equation for the nonhomogeneous medium corresponds to the integral equation for the field E. Methods of functional analysis are used to show that the solution of the equation can be represented in the form of the Neumann series, which in general satisfies the conditions of uniform convergence. Certain limitations on the dielectric permittivities of the auxiliary medium are derived as sufficient conditions for the convergence of the series.
Level Ordering in II3‐‐V2 Semiconducting Compounds
Authors: Cisowski J.
Published: July 2007

The quasicubic model as well as the known value of the crystal field splitting of Cd3As2 are used to calculate this splitting in other II3–V2 compounds. The ordering of p‐like levels at the Γ‐point is determined and compared with recently available experimental data.
Polariton and Spatial Dispersion Effects in Exciton Spectra of Xenon Cryocrystals
Authors: Fugol I. Ya. , Grigorashchenko O. N. , Savchenko E. V.
Published: July 2007

Transmission and luminescence spectra of Xe cryocrystals are studied experimentally in the region of the n = 1, Γ(3/2)‐resonant transition at 5 to 80 K. On the basis of the polariton theory and with allowance for spatial dispersion, the optical characteristics of solid Xe are calculated and show good agreement with experiment. The effects of the Raman scattering of polaritons, two‐phonon process contributions, and the existence of temperature barriers in scattering are discussed.
Properties of Exciton Polaritons Studied in a One‐Dimensional Model
Authors: Balslev I. , Stahl A.
Published: July 2007

Exciton polaritons are traditionally considered as composite particles formed from bare excitons and photons. In a recently developed alternative approach one starts from polariton theory in configuration space and finds excitons as resonances in the polariton system. The relation between the two methods is explored in the present paper. Using a simplified one‐dimensional model the configuration space system is solved exactly for bulk and halfspace geometry, partly by numerical methods. The solutions are in good agreement with experimental reflection spectra. In order to rederive the results of traditional theory one has to apply aproximations: The “rigid‐exciton approximation” for bulk solutions and the adiabatic approximation for halfspace geometry. The influence of these approximations is discussed.
Transport Properties and Plasma Resonance of Bismuth Selenide Crystals Doped with Cadmium
Authors: Horäk J. , Koudelka L. , Klikorka J. , Šiška L.
Published: July 2007

Electrical conductivity, Seebeck coefficient, Hall constant, and plasma resonance frequency are determined for samples of Bi2Se3 crystals, pure and doped with Cd. The concentration of the free carriers is determined from the measured transport parameters and compared with the concentration of cadmium atoms as determined by atomic absorption technique. It is found that each Cd atom built into the crystal lattice removes approximately one conduction electron. On the basis of this finding and using the ideas about the bonding conditions in the lattice, the nature of the point defects brought about by introducing Cd atoms into the Bi2Se3 crystals is describecd. The Cd atoms occupy the sites of Bi atoms, which results in Cd′Bi defects of acceptor nature. Finally, a comparison of the properties of the impurities from the group 2b of the periodic system is made.
Model of Self‐Consistency Simulation in Constructing a Non‐Self‐Consistent MT Potential for Metals
Authors: Stepanyuk V. S. , Evdokimenko O. A. , Katsnelson A. A. , Shpotin I. S. , Yastrebov L. I.
Published: July 2007

It is shown that the use of the Friedel sum rule in constructing the “muffin‐tin” potential for metals can be considered as the procedure of self‐consistency simulation. Energy band structure calculations of V and Cr are made both with the use of the Friedel sum rule and without it. Comparison of the results with the self‐consistent calculations which were made earlier show good agreement when the Friedel sum rule is used. The change of the energy band structure in the process of lattice dilatation is investigated.
Dielectric Relaxation in Polar Liquid Crystals
Authors: Buka A. , Leyvraz F.
Published: July 2007

A model is suggested for interpreting the experimental dielectric dispersion data in nematic liquid crystals. The high‐frequency dispersion is observed in both, parallel and perpendicular alignment of substances with only a molecular dipole moment parallel to the long axis of the molecule. In the absence of a perpendicular dipole moment component these high‐frequency absorptions cannot be associated with rotation about the molecular axis. The model is based on Kubo's linear response theory and describes the dipole relaxation processes in frames of rotational diffusion. Results are compared with experimental data obtained on 4‐cyano‐4′‐octylbiphenyl.
Vacancies in α‐Zirconium
Authors: Ong C. K.
Published: July 2007

A Lennard‐Jones potential is used to calculate the formation and binding energies for a monovacancy, divacancy, and trivacancy in α‐Zr. Stable divacancy and trivacancy configurations are found. The displacement fields, dipole force tensors, and relaxed volumes of the vacancy clusters are also calculated.
Nonequivalence of De Launay and Clark, Gazis, and Wallis Angular Force Models
Authors: Ramamurthy V.
Published: July 2007

The angular force models of De Launay and Clark, Gazis, and Wallis are analysed by resolving the atomic displacements along three mutually perpendicular directions. It is shown that the CGW model which neglects a two‐body force component perpendicular to the plane of the triangle is not equivalent to the DAF model which neglects the three‐body forces confined to the plane, for any crystal structure and all the earlier claims regarding their equivalence are therefore spurious. The equivalence between the angular force constants of these models, the relations between these and other force constant models as well as the role played by the axially symmetric forces, in the case of b.c.c. and f.c.c. structures are discussed.
Investigation of Transport Coefficients in Semimetals by the Variational Method I. General Solution of the Problem
Authors: Gitsu D. V. , Golban I. M. , Kantser V. G.
Published: July 2007

A variational procedure for the solution of the Boltzmann equation with an arbitrary number of variational parameters is developed. In the frame of the method it is possible to carry out the optimization of trial function, as well as to check the convergence of the solution. It is shown that in semimetals the probability matrix of charge carrier scattering on acoustic phonons entering the expression for the collision operator has a non‐diagonal form in the coordinate system of the effective mass tensor. General expressions are obtained for the transport coefficients allowing to determine their numerical values.
Interband Magnetoreflectivity at Pb1−xSnxSe Single Crystals
Authors: Bange K. , Liebegall A. , Lorentz B.
Published: July 2007

For Pb1‐xSnxSe single crystals with x = 0.035, 0.045, and 0.070 the interband magnetooptical reflectivity (IMOR) is studied using a CO2 laser emitting between 10.1 and 10.7 μm and variable magnetic fields up to 5.5 T. The spectra are obtained with the samples in Faraday configuration for left circularly, right circularly, and linearly polarized (lcp, rcp, and lp) radiation. The experimentally determined transition energies lead to band parameters calculated with a six‐band model, which are discussed in terms of their dependence on alloy composition.
Bulk Photovoltaic Effect in a Ferroelectric Crystal A Model Calculation
Authors: Presting H. , Von Baltz R.
Published: July 2007

A numerical investigation of the bulk photovoltaic tensor for a ferroelectric crystal is presented. The studies are based on a simple two‐dimensional LCAO model which preferably can be treated analytically. In contrast to previous studies, however, the complete band structure and wave vector dependence of the transition matrix elements are taken into account. This paper also reports the first numerical application of the R‐vector concept which is recently developed for the intrinsic bulk photovoltaic effect.
EPR Investigation of Manganese–Boron Pairs in Silicon
Authors: Kreissl J. , Gehlhoff W.
Published: July 2007

After manganese doping of low‐resistivity B‐doped p‐silicon an EPR centre is detected, which could be identified in accordance with Ludwig and Woodbury as a manganese‐boron pair, where a interstitially incorporated Mn2+ ion is located in the immediate vicinity of a B− ion on a substitutional site. It is shown, that compared to the main direction H ∥ C3 and H τ C3 the much more complex spectra observed for arbitrary directions of the magnetic field are caused by the simultaneous appearance of “allowed” and “forbidden” hyperfine transitions owing to the comparable magnitudes of the Zeeman splitting and fine structure splitting in the X‐band. Additionally a weak dependence of the magnitude of the local trigonal crystal‐field distortion at the manganese site on the associated boron isotope 10B/11B is proved (isotope effect in the fine structure).
Role of Zero‐Point Motion and Three‐Body Effects in the Study of Crystal Properties of Rare Gas Solids
Authors: Singh R. K. , Neb D. K.
Published: July 2007

The role of zero‐point motion and three‐body interactions (TBI) is investigated in describing the numerous crystal properties of rare gas solids (RGS). The model used is made less parametric in nature by incorporating the effect of TBI via overlap integrals evaluated by Hafemeister. Remarkably good agreement is achieved between theoretical and experimental results on cohesive, harmonic, and anharmonic elastic and thermophysical properties of RGS.
Ion Implantation in Alkaline Earth Oxides
Authors: Henderson B. , Garrison A. H.
Published: July 2007

Spectroscopic investigations of defects are made in alkaline earth oxides implanted with 400 keV Li+ or Na+ ions. Detailed comparisons of ESR, optical absorption, and luminescence spectra confirm that the predominant point defect is the F+ centre. Smaller concentrations of F2 and F centres are also produced. V− centres and isolated anion vacancy centres are not produced by irradiation. Annealing studies demonstrate that colloid centres grow during annealing above 500 K.
Absorption and Stress‐Induced Linear Dichroism of Pb++ Centres in KCl and RbCl
Authors: Schmitt K.
Published: July 2007

The optical absorption and the stress‐induced linear dichroism (SLD) of Pb++‐centres in KCl and RbCl are investigated in the temperature range 4 to 200 K. Using moments analysis the energy parameters of the systems, the effective electron‐phonon‐coupling constants of the |A> state, and the effective frequencies of the A1g, E2g, and T2g interaction modes are determined. The temperature dependence of the B‐band and the splitting of the C‐band give additional information about the dynamical properties of the systems. The results imply that in either case the electronlattice interactions of the 3T1u state and of the 1T1u state are of comparable strength.
Anharmonic Coupling of Phonon Modes in Mixed ZnxCd1−xSe Crystals
Authors: Valakh M. Ya. , Lisitsa M. P. , Pekar G. S. , Polysskii G. N. , Sidorenko V. I. , Yaremko A. M.
Published: July 2007

The vibrational properties of ZnxCd1–xSe phonons are studied using Raman scattering. The change of the LO‐phonon spectrum versus crystal composition is found to be of the one‐mode type. The TO‐phonon behaviour is much more complicated. It exhibits rather anomalous features in the line shape and TO‐mode frequency versus crystal composition as well as temperature. The above phenomena are interpreted in terms of the anharmonic coupling between TO‐mode and two‐ phonon states. This coupling is well described by the theory developed.
Analysis of Crystal Binding and Grüneisen Parameter in Cesium Halides, silver Halides, and Alkaline Earth Oxides
Authors: Shanker J. , Singh K.
Published: July 2007

An analysis of the crystal binding energies and the Grüneisen parameter γ is performed in CsCl, CsBr, CsI, AgCl, AgBr, MgO, CaO, SrO, and BaO crystals. Values of cohesive energy, the Grüneisen parameter, and its volume derivative are calculated for all the crystals under study. Different theories of γ are used and compared with each other. Various potential functions for the repulsive energy are used in the calculations. The van der Waals interactions are also taken into account. The potential parameters for the repulsive energy are determined using input data on interionic separation and bulk modulus. The Born‐Landé inverse power and the Born‐Mayer exponential forms are adopted for repulsive interactions upto second neighbours. The results obtained are compared with available experimental data.
Low temperature conductivity and optical transitions of a two‐dimensional disordered semiconductor under weak localization conditions
Authors: Bonch‐Bruevich V. L. , Nguyet To Thi Bich
Published: July 2007

Two problems are considered of the theory of two‐dimensional disordered semiconductors. The first one is that of a temperature dependence of the static conductivity when the Fermi level lies in the weak localization region. The second one concerns the frequency dependence of the light absorption coefficient due to electron transitions between the strongly (exponentially) and weakly localized states. It is shown that the latter experiments might reveal the form of the density of states in a weakly localization region.
Effective interatomic forces from one‐particle crystal field parameters
Authors: Adam S. , Adam Gh. , Corciovei A.
Published: July 2007

Theoretical results are obtained for the crystal field coefficients which enable us to develop an approach to the use of the crystal field data for the derivation of information on the effective interatomic forces in crystals. The method is applied to the magnetic Sm3+ ion in SmCo5, and it is shown to provide valuable results both for the effective interatomic potential and for the consistency of various sets of crystal field parameters previously proposed in the literature.
Curie temperature and short‐range atomic order in amorphous ferromagnets
Authors: Maksymowicz A. Z.
Published: July 2007

A simple description of amorphous AcB1–c alloys with different coordination numbers of the components of the alloy, ZA = ZB, is discussed. Curie temperature is calculated and mean field approximation results are compared with those obtained by a Green function technique for the Ising model with S = 1/2. The chemical short range order is accounted for and its parameter is calculated for the equilibrium state at temperature T. Fluctuations of coordination numbers and exchange integrals are not considered to get a more clear picture on how the Curie temperature is affected by ZA ≠ ZB. For a diluted ferromagnet with ZB of nonmagnetic atoms smaller than ZA, the Curie temperature increases and the critical concentration for magnetic solution is shifted to lower values. Short range atomic order, which favours A–B pairs, shows opposite tendency.
On the coexistence of superconductivity and itinerant ferromagnetism
Authors: Kolley E. , Kolley W.
Published: July 2007

The interplay of superconductivity and ferromagnetism in an itinerant electron system is described by attractive contact and repulsive Hubbard interactions within a substitutionally disordered tight‐binding model. Functional integral formalism at nonzero temperatures is employed in going over from Grassmann variables to collective Bose fields to derive microscopically the quadratic and quartic terms in the loop expansion of the effective action. The configurational averaging is performed on the mean field level to find out a Landau‐type theory for two biquadratically coupled coherent order parameters. It is proved that the coexistence region for the superconducting and ferromagnetic phases cannot be reached in the percolation limit of AxB1–x alloys. For testing the present method the results of the itinerant and localized spin models are compared.
On the theory of time‐resolved band‐tail luminescence in amorphous semiconductors
Authors: Esser B.
Published: July 2007

The time‐dependent moments of a luminescence band due to radiative recombination within electron‐hole pairs localized in band tail states are calculated. Besides the radiative process a competing non‐radiative process by tunneling of the excited electrons (or holes) to defect centres is assumed. The time dependence of the centre of the band ωc(t) and the linewidth σ(t) are shown to be determined by the time evolution of the tail region from which the electrons effectively recombine at t as well as from the time‐dependent electron‐hole separation in the Coulomb interaction. These two mechanisms act in an opposite way and as a result a non‐monotonous behaviour in both ωc(t) and σ(t) observed experimentally is obtained.
On the diamagnetism of deep impurities in quantized semiconductor films
Authors: Imamov E. Z. , Krevchik V. D.
Published: July 2007

The diamagnetic susceptibility (DS) of one‐electron deep impurity centres (DIC) in quantized semiconductor films is calculated. For electrons in bound DIC states Lucovsky's model with the wave function meeting the boundary conditions on the film surface is taken. For certain values of the impurity centre coordinates the DS dependence on film thickness L with fixed zero range potential capacity is studied. The results of Lucovsky's model for massive semiconductors in the limiting case L → ∞ are obtained.
Study of lattice statics and allied properties of zincblende‐type compound semiconductors
Authors: Singh R. K. , Singh R. D.
Published: July 2007

An interionic potential model is developed which incorporates the effects due to the long‐range Coulomb and three‐body interactions and the short—range overlap repulsion operative up to the second‐neighbour ions, and van der Waals dipole‐dipole and dipole—quadrupole attractions. The use of this potential for comprehensive calculations yields satisfactory prediction of the lattice statics and allied properties of zincblende‐type compound semiconductors. These successes reveal the importance of van der Waals and three‐body interactions in these semiconductors.
Analysis of interionic potentials in alkali chalcogenide crystals
Authors: Jain V. K. , Shanker J.
Published: July 2007

An analysis of the interionic potentials is performed in 14 alkali chalcogenide crystals. New values of the van der Waals potentials are used. Different values of repulsive hardness parameters are introduced for different nearest‐neighbour and next nearest‐neighbour pair interactions. Cohesive energies, bulk modulus and its pressure derivative are calculated for the entire family of crystals under study.
On a ferromagnet coupled to the paramagnetic system: Fluctuations and spin reorientation
Authors: Loos J.
Published: July 2007

The Stratonovich‐Hubbard functional integration method is applied to the isotropic ferromagnet coupled by an antiferromagnetic exchange to a paramagnetic system. Such system represents a simple model e.g. for rare earth iron garnets, The general correspondence between the quantum statistics and the classical description leading to the effective classical Hamiltonian of the fluctuations is outlined. This formalism is applied to the spin‐reorientational phase transition.
Simple results for one‐dimensional periodic potentials
Authors: Pacheco MÓNica , Claro F.
Published: July 2007

A simple solution is derived for an arbitrary one‐dimensional potential in terms of basis functions in a unit cell and Chebyshev polynomials. The effect on the allowed energy bands of a commensurate disturbance is also discussed.
Optimization of tosi‐fumi ionic radii for F.C.C. alkali halide crystals
Authors: Damm J. Z. , Chvoj Z.
Published: July 2007

On the basis of several empirical relations between a property (mostly connected with the presence of some point defects) on the one hand and the radii ratio (pj) of the lattice ions and interionic distance (cj) on the other, it is possible to raise the accuracy of Tosi‐Fumi ionic radii values. Pertinent calculations are performed for nine alkali halides (chlorides, bromides, and iodides of sodium, potassium, and rubidium). Using above empirical relations in which accurate cj and pj values (the latter obtained in this work) are introduced, in most instances a very good agreement is ascertained between calculated and experimental values related with appropriate properties.
The band structure of Cd3P2 in the presence of a magnetic field
Authors: Singh M. , Cisowski J. , Wallace P. R. , Portal J. C. , Broto J. M.
Published: July 2007

The band structure of Cd3P2 is presented on the basis of Bodnar's model which is extended by Wallace in presence of magnetic field. The oscillations of the Fermi level with magnetic field are calculated and it is found that the amplitude of the oscillations in Cd3P2 is larger than in Cd3As2. The effect of the so‐called free‐electron term is included in the calculation of the g‐factor and cyclotron effective mass. The correction due to the free‐electron term in the g‐factor is smaller (gf ≪ 2) than anticipated and depends on energy. Another interesting result of the calculation is that there is linear relationship between cyclotron effective mass and energy.