bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vacancy defects in as‐grown and nº‐irradiated GaP and GaAs1−xPx Studied by Positrons
Authors: Dlubek G. , Brümmer O. , Polity A. 
Published: January 2007

AbstractMeasurements of positron lifetime τ and of the shape parameter S of the Doppler‐broadened annihilation line are used to study bulk and defect properties in GaP and GaAs1−xPx. τ and S decrease linearly with the composition x of GaAs1−xPx layers. A second lifetime component (τ2 = 290 ps) observed in as‐grown GaP is attributed to stoichiometric P vacancies. After neutron irradiation of GaP and GaAs0.13P0.87 positrons are trapped by Ga vacancies (τ2 = 250 ps). These vacancies anneal out in two stages at 200–550 °C and 550–800 °C.
Electrical properties of GaAs induced by the metastability of EL2 defect
Authors: Walczak J. P. , Kaminska M. , Baranowski J. M. 
Published: January 2007

AbstractMetastable properties of EL2 defect in undoped semiinsulating GaAs have been studied using photocurrent and thermally stimulated current techniques (TSC). The experimental data suggest that light induced defect reaction takes place when EL2 is transferred to its metastable state.
Crystallization kinetics of MgSO4 · 7 H2O in presence of tenside
Authors: König An. , Emons H.‐H. 
Published: January 2007

AbstractThe effect of sodium dodecyl sulfate (SDS) on crystallization kinetics and crystal habit of MgSO4 · 7 H2O from aqueous solutions at 25 °C was investigated in batch experiments. It highly depends on the supersaturation level. Both increasing supersaturation and rising concentration of the tenside promote the production of needle‐like crystals but the influence of the driving force is much more pronounced. SDS increases the crystallization rate and the linear crystal growth rate in length direction of the crystals. To a high degree it also influences properties of the crystallizing solution such as surface tension and viscosity.
Ultrasonic relaxation studies across N‐I transition in the liquid crystal p‐cyanophenyl trans‐4‐pentyl cyclohexane carboxylate
Authors: Venkatacharyulu P. , Gupta A. V. N. , Rao J. V. 
Published: January 2007

AbstractThe variation of ultrasonic velocity with temperature in the liquid crystal p‐cyanophenyl trans‐4‐pentyl cyclohexane carboxylate at four different fixed frequencies is studied. From the observed data relaxation parameters like adiabatic relaxation time, velocity at infinite frequency and velocity at zero frequency, in the vicinity of isotropic‐nematic transition are sutied. The relaxation mechanism is discussed.
Orthorhombic — tetragonal phase transition and oxygen index of YBa2Cu3O6+δ
Authors: Pietraszko A. , Wolcyrz M. , Horyń R. , Bukowski Z. , Lukaszewicz K. , Klamut J. 
Published: January 2007

AbstractThe orthorhombic — tetragonal phase transition of YBa2Cu3O6+δ has been investigated by X‐ray powder diffraction methods. The transition is of the second order or very close to second order and no coexistence of tetragonal and orthorhombic phases has been observed. The transition strongly depends on the oxygen index δ which changes with temperature. Typical patterns of the triplet 006, 020, and 002 obtained by precise X‐ray powder diffraction measurements have been presented and shown to be useful for identification of YBa2Cu3O6+δ and estimation of oxygen index δ.
Optical properties of helium implanted inp single crystals
Authors: Hörig W. , Orlenko V. F. , Neumann H. , Ascheron C. 
Published: January 2007

AbstractOptical absorption spectra of helium implanted InP single crystals are measured in the photon energy range from 0.9 to 1.3 eV. It is found that helium implantation gives rise to exponential absorption tails below the fundamental edge. The absorption coefficients as well as the characteristic tailing energy increase with increasing fluence.
X‐Ray topographic characterization of α‐Fe2O3 single crystals obtained by chemical transport with TeCl4
Authors: Vassilev I. S. , Toshev A. , Peshev P. , Botev P. A. 
Published: January 2007

AbstractThe method of Lang is used to study the defect structure of „as‐grown”︁ hematite crystals obtained by chemical transport with TeCl4. The presence of twin boundaries, dislocations and crystallites built in the platelet matrices is established. Considerable differences in density and distribution of the crystal disturbances are observed with samples grown under the same experimental conditions. In some cases the real structure is found to be nearly perfect.
Combined investigations of NiAl alloys by means of X‐ray photoelectron spectroscopy, compton gamma scattering and positron annihilation
Authors: Hoppe W. , Marx U. , Dlubek G. , Brümmer O. 
Published: January 2007

AbstractThe results of measurements of Compton profiles, photoelectron spectra, positron annihilation curves, and lifetime spectra of several NiAl alloys are discussed in terms of bonding and stability in transition metal aluminides.The interpretation of experimental Compton profiles suggests a transfer of nearly‐free electrons from Al sites to more localized d‐like states on Ni‐sites. The transfer increases with Al contents up to 50 atomic percent. From X‐ray photoelectron spectra in the case of Al‐rich alloys a different behaviour follows. The results support a model established by Wenger. Following this in the composition range above 50 percent Al no further charge is transferred to Ni cells. The Ni d states seem to be occupied in the Al‐rich alloys. A preferential annihilation of positrons in Ni cells is though to have its origin in the enhanced negative charge of these cells caused by charge transfer.
Thermally activated de‐excitation of the EL2 metastable state in GaAs
Authors: Trautman P. , Kamińska M. , Baranowski J. M. 
Published: January 2007

AbstractMeasurements of absorption in the near infrared have been performed on n‐type and undoped semi‐insulating GaAs containing EL2 the main native defect in GaAs. The whole band of absorption related to EL2 disappeared after 1 μm light illumination when the crystal was cooled to helium temperatures. Measurements of the thermally activated recovery of EL2 absorption have been made. The rate of the de‐excitation is well described by the formula:r = 1.7 · 1012 · exp (−0.36 eV/kT) + 1.6 · 10−9 · n · exp (−0.085 eV/kT) s−1 where n [cm−3] is the concentration of free electrons.
Positron annihilation study in Ca2+ and Sr2+‐doped KCl
Authors: Nancheva N. M. , Terzijski K. I. , Mishev P. L. 
Published: January 2007

AbstractPositron lifetime and three photon annihilation measurements are reported in KCl:Ca2+ and KCl:Sr2+. The present results clearly demonstrate that the positron essentially depends on the kind of Me2+ and impurity concentration in these crystals.
Dependence of ortho‐positronium pick‐off annihilation lifetime on free volume in water‐methanol mixtures, and positronium bubble formation
Authors: Jerie K. 
Published: January 2007

AbstractSizes of free volume were quantitatively calculated for water‐methanol mixtures by means of the Kincaid and Eyring method. The results were discussed in relation to the pick‐off annihilation lifetime of ortho‐positronium in these mixtures. The existence of two ranges of methanol METH concentration in water was observed, within which the dependences of lifetime of o‐Ps annihilating by the pick‐off process τ2 on the calculated free volume size are quite different. The problem that the calculated free volume was too small for the existence of o‐Ps could be eliminated by the equilibristic formation of a bubble around o‐Ps. Correlation was shown between the free volume radii and bubble radii. The obtained results testify to the existence of the strong dependence of τ2 on the free volume radii. The peculiar shape of this dependence confirms the existence of the clathrate structure in METH‐H2O mixture.
Positron camera with high‐density avalanche chambers
Authors: Manfrass P. , Enghardt W. , Fromm W. D. , Wohlfarth D. , Hennig K. 
Published: January 2007

AbstractThe results of an extensive investigation of the properties of high‐density avalanche chambers (HIDAC) are presented. This study has been performed in order to optimize the layout of HIDAC dectetors, since they are intended to be applied as position sensitive detectors for annihilation radiation in a positron emission tomograph being under construction.
Wachstumsmorphologie von LiNbO3‐einkristallen bei der züchtung nach dem czochralski‐verfahren unter der einwirkung eines elektrischen feldes
Authors: Reiche P. , Bohm J. , Hermoneit B. , Rudolph P. , Schultze D. 
Published: January 2007

AbstractDie Wachstumsmorphologie von Lithiumniobat‐Einkristallen, die nach der Czochralski‐Methode gezüchtet wurden, wird als Ergebnis des Wechselspiels von atomar rauhen und atomar glatten (Facetten‐) Flächen beschrieben. An glatten Flächen ist die Grenzflächenspannung zwischen Kristall und Schmelze merklich größer als an rauhen Flächen, was bei bestimmten Orientierungen der Facetten zu einer kapillaren Depression des Meniskus führen kann. Daraus resultierende hydrostatische Instabilitäten werden als Ursache für die spontane Keimbildung und Entstehung von Polykristallen angesehen.Durch Anlegen eines elektrischen Feldes zwischen Kristall und Schmelze wird die Grenzflächenspannung verringert. Das führt unter anderem zu verbesserter Benetzung der Facetten durch die Schmelze, die Entstehung der Polykristalle wird unterdrückt.
Calculation of temperature fields in a cylindrical heater system
Authors: Deus P. , John M. , Krause H. , Sauermann H. 
Published: January 2007

AbstractA model for calculation of time dependent temperature fields in a cylindrical furnace used for crystal growth experiments is described. The comparison of the calculated and the experimental temperature profiles shows good agreement in the stationary case and the suitability of the model for the prediction of static temperature fields on the basis of given heating power distributions, and vice versa.
Transient regimes in the growth of large‐diameter crystals
Authors: Nalbandyan G. H. , Nemenov V. A. 
Published: January 2007

AbstractThe behaviour of crystallization rate and interface position under the change of Czochralski growth system parameters is theoretically and experimentally investigated for the case of large diameter crystals growth. It is shown that the large value of crystal diameter leads to the inertia and nonmonotonic character of system relaxation after the perturbation. The possibility of hesitative nonstability is discussed. The transient regimes in the growth of 30 cm diameter KCl single crystals are investigated experimentally. The behaviour of crystallization rate differs from the case of small diameter crystals and corresponds to the results of theoretical analysis.
On the morphological instability of growing crystals (I) morphological peculiarities of the transition shapes of crystals in diffusion‐controlled regime of growth
Authors: Nanev Christo N. 
Published: January 2007

AbstractThe shape and size of the gross morphological defect which occurs (in the form of a depression) as a result of the diffusion inhomogeneity in the matter supply on the growing crystal face with supercritical dimensions are investigated. The transition shapes of similar skeletal crystal faces are determined by considering the configuration of the steps which are moving (and accumulating) from the edge toward the centre of the crystal face. The basic parameter which is evaluated, is the width of the macroscopically flat periphery which grows around the depression and its alteration when the crystal is enlarged. The theoretical analysis is carried out by presuming that no transportation of crystallizing material occurs parallel to the crystal face. The calculations are based on the different thicknesses of the Nernst diffusion layer, a magnitude which can be easily determined experimentally by some interferometric technique, over the various regions of the growing face.
Bridgman‐stockbarger growth and spectral characteristics of Al2O3:Ti3+ single crystals
Authors: Peshev P. , Delineshev S. , Petrov V. , Manuilov N. , Yankov P. , Bachvarov I. 
Published: January 2007

AbstractSingle crystals of Al2O3:Ti3+ (Ti ranging from 0.1–1.5 at.%) are grown by the Bridgman‐Stockbarger method from a mixture of Al2O3 and Ti2O3 in a medium of 90% Ar and 10% H2. The radial distribution of Ti3+ in the crystals is determined by measuring the optical transmission. The absorption spectra of the crystals and the luminescence spectra of Ti3+ in the Al2O3 matrix are obtained and the crystals fluorescence lifetime is determined. The optical characteristics of the crystals have shown good agreement with the corresponding characteristics of Al2O3:Ti3+ crystals grown by other methods.
Structure refinement of paranatrolite by X‐ray diffraction
Authors: Pechar F. 
Published: January 2007

AbstractParanatrolite, Na2Al2Si3O10·3H2O, monoclinic (space group Cc), but described here the pseudo‐orthorhombic setting of Fd, with a = 18.998(3) Å, b = 19.018(3) Å, c = 6.579(2) Å, β = 90.37°(1) in analogy to scolecite. 225 parameters, including hydrogen atoms, were refined anisotropically from 1400 X‐ray diffraction reflections, the final conventional R‐value being 0.036. Tetrahedral arrangement of Si and Al are of O—D character as well as the Na+ ions. Hydrogen bonding is discussed.
Structural energetics of the intermetallic compounds CaMg2 and CaAl2
Authors: Radwan A. M. 
Published: January 2007

AbstractThe structures of the Laves phases CaMg2 and CaAl2 are investigated using the optimized model potential. Charge transfer, which is taken into account in an approximate and simple way, plays an important role in the determination of the stable crystal structures of both CaMg2 and CaAl2.
Radial distortions of the fermi surfaces of rubidium and cesium
Authors: Radwan A. M. 
Published: January 2007

AbstractThe radial distortions of the Fermi surfaces of Rb and Cs are calculated in the three principal directions 100, 110 and 111. The calculations are carried out using different values of the model potential parameters and the effective charge. Our results are compared with available experimental and theoretical ones.
Crystal structure of 4,5‐dihydro‐6‐(2‐thienyl)‐3(2H) pyridazinone azine, (C16H16N16S2)
Authors: Farag I. S. Ahmed , Kordy M. A. El , Will G. 
Published: January 2007

AbstractMr = 484, monoclinic, P 21/c, a = 5.567(1), b = 7.857(2), c = 19.194(10) Å, β = 99.97(3)°, V = 826.9 Å3, Z′ = 2, Dx = 1.43 g · cm−3, F(000) = 372, MoKα, λ = 0.71069 Å, μ = 0.328 mm−1, final R = 0.055 for 889 observed reflections, T = 293 K. The compound was prepared from a direct unusual reaction of 6‐(2‐thienyl)‐2,3,4,5‐tetrahydropyridazine‐3‐one with hydrazine hydrate. The structure was solved by direct methods and refined by full‐matrix least squares. The molecule in the solid state consists of a dimer with its two equivalent halves related by a center of symmetry at the middle of the NN bond. Each molecular fragment is nearly planar and the NN bond between the two halves is 1.296(5) Å indicating that it is a partial double bond.
The effect of temperature on the raman spectra of strontium formate dihydrate single crystals
Authors: Prieto A. C. , Rull F. , Gonzalez A. , Martin F. 
Published: January 2007

AbstractThe temperature dependence of the polarized Raman Spectra (3000 cm−1 – 10 cm−1, between 293 K and 10 K) of Sr(HCOO)2 · 2H2O(2D2O) and partially deuterated samples is reported. From the analysis of the internal and external modes associated with water molecules and formate ions a phase transition is deduced. This is interpreted on the basis of the positional disorder of the hydrogen atoms, situated in non‐equivalent lattice positions at low temperature.
Influence of view angle of radiation and heat of fusion on the GaAs bridgman crystal growth
Authors: Frühauf J. 
Published: January 2007

AbstractThe paper is concerned with the numerical simulation of temperature distributions within the ingot. The effective field of view of heat exchange by radiation depending on the difference in the radii of the ingot and furnace wall flats the axial temperature gradient in the ingot and influences the position of the solid‐liquid interface. In the vicinity of this interface the heat of fusion flats and increases the temperature gradient in the liquid and the solid respectively. Thereby the curvature of isotherms is changed, too.
Crystal and molecular structure of 14‐desoxy‐14ß‐azido‐digitoxigenin‐3‐acetate
Authors: Scharfenberg‐Pfeiffer D. , Höhne E. , Megges R. , Schmidt H.‐J. 
Published: January 2007

AbstractThe crystal and molecular structure of 14‐desoxy‐14ß‐azido‐digitoxigenin‐3‐acetate was determined by X‐ray analysis. The compound crystallizes in the orthorhombic space group P 212121 with four molecules C25H35N3O4 in the unit cell. The lattice parameters are a = 8.975, b = 13.698, and c = 18.958 Å. The structure was solved by direct methods and refined by least‐squares procedures up to the discrepancy factor R = 0.041.
Twinning of crystals and crystal moduli conception
Authors: Lemeshko V. V. , Obukhovsky V. V. , Rez J. S. 
Published: January 2007

AbstractAn idea of crystal moduli (CM) as minimum aggregates for constructing of complex crystal lattices is introduced. CM arrangement in crystals is described by means of packing groups Ĝ. Twin structure constructions are demonstrated on the base of CM conception for LiNbO3, ZnS and KTiOPO4 crystals. There are next advantages of CM conception: a) Physically not verified versions of twinning appearing in other theories (Klassen‐Nekludova; Blistanov et al. 1975, 1976a) are automatically excluded; b) CM method allows to describe crystal twinning when transition strata between twin blocks appear. The connection between CM conception and crystal growth mechanism is discussed.
An effect of oxygen pressure on the process of monocrystallization of the MnaZnbFe2O4 manganese‐zinc ferrites
Authors: Guzik E. , Fitzner K. 
Published: January 2007

AbstractThe present paper relates theoretical assumptions concerning the pressure of oxygen required for the process of monocrystallization of the MnaZnbFe2O4 manganese‐zinc ferrites.A general analysis of the equilibrium diagram ZnMnFeO was carried out, taking into account the pseudobinary ZnFe2O4MnFe2O4 system for the case of the formation of the above mentioned ferrite. At the same time, it was assumed that the base material (a polycrystal) for the unidirectional solidification in a Bridgman system would be formed of two compounds, i.e.f. ZnFe2O4 and MnFe2O4.It was stated that the monocrystallization of manganese‐zinc ferrites should be carried out in the working chamber of a furnace at a pressure of oxygen amounting to from several tenth to several megapascals, the values of these pressures depending on the composition of the crystalline phase (the values of X2, MnFe2O4 and X1, Fe2O4 used in Equation (12)).
Microstrain and lattice parameter of pure and Li2O‐doped nickel oxide solid
Authors: El‐Shabiny A. M. , El‐Shobaky G. A. , Hewaidy I. F. , Ramadan A. A. 
Published: January 2007

AbstractPure and Li2O‐doped NiO were prepared by thermal decomposition of pure and LiOH‐treated Ni(OH)2 at temperatures between 500 and 800 °C. The lattice parameter, residual microstrain and crystallite size were determined using X‐ray diffraction analyses.
Modelling of mechanism of agglomeration of KCl crystallization
Authors: Schmok K. 
Published: January 2007

AbstractThe article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.
On the effect of an Si3N4 barrier layer over GaAs1−xPx during Zn diffusin: A photoluminescence analysis
Authors: Vigil E. , Zehe A. , Gracia M. , Martinez M. G. 
Published: January 2007

AbstractAn Si3N4 barrier layer on top of a GaAs1−xPx layer is applied to diminish the out‐diffusion of matrix atoms during the formation of p‐n junctions by Zn diffusion. An extended photoluminescence analysis of protected and nude but otherwise identical samples is carried out in order to compare the effects introduced by the barrier layers. Samples obtained from two different diffusion processes establishing the p region of a low and high impurity concentration, are studied. Spectra evolution with temperature is obtained from 10 to 300 K. Differences between spectra corresponding to samples diffused with and without an Si3N4 barrier layer indicate that nonradiative center concentrations are lowered in the presence of the barrier layer.
The influence of the terminal alkyl chain on the orientational order of solute molecules dissolved in a nematic matrix
Authors: Pelzl G. , Isenberg A. , Demus D. 
Published: January 2007

AbstractThe orientational order of five homologous 4‐n‐butyl 4‐n‐alkyloxyazobenzenes in the same nematic matrix has been measured. It was found that the orientational order of the solute molecules increases with increasing length of the terminal alkyl chain.
Dielectric studies on Ba(NO3)2
Authors: Srinivas M. , Sirdeshmukh Lalitha 
Published: January 2007

AbstractSingle crystals of Ba(NO3)2 were grown by slow evaporation of aqueous solution. The dielectric constant (ϵ) and loss (tan δ) have been measured in the frequency range of 100 Hz to 100 KHz at temperatures ranging from room temperature to 400 °C. A.c. conductivity (σ) is calculated from the data on ϵ and tan δ. ϵ, tan δ, and σ were found to show anomalies around 270 °C. The results are discussed in the light of order‐disorder phase transition.
The dependence of the surface energy of regular clusters and small crystallites on the particle size
Authors: Müller E. , Vogelsberger W. , Fritsche H.‐G. 
Published: January 2007

AbstractWhereas in the case of liquids the theories on the dependence of the surface energy on the particle size are uniform in general, describing a decrease of σ with decreasing particle size, in the case of small solid particles also a dependence with the inverse sign has been assumed in the literature.Equations of the size dependence of σ and γ are derived for icosahedral and cuboctahedral clusters of noble gases considering interactions only with next neighbours. It will be shown that the character of the size dependence is dominated by the choice of the position of the dividing surface. Compared to that, such equations are derived also for ion crystallites. The resulting differences can be explained by the differences in structure and bonding.
Oxygen potentials, stoichiometry, superconducting, and magnetic properties in the YBaCuO system
Authors: Krabbes G. , Auerswald G. , Bartl A. , Eschrig H. , Lippold B. , Ritschel M. , Vinzelberg H. , Wolf E. , Wiesner U. 
Published: January 2007

AbstractThe relationship between stoichiometry in YBa2Cu3Ox and oxygen potential was investigated by barometry and compared with in‐situ X‐ray diffraction experiments between 300 and 1000 °C (6 < x < 7). The physical properties are influenced even by small deviations in x. Y2BaCuO5 was included in the investigations and found to be antiferromagnetic with TN ≈ 30 K.
Investigations of curved graphite crystals for the use as X‐ray monochromators
Authors: Arnhold R. , Kauter S. 
Published: January 2007

AbstractX‐ray investigations on curved graphite crystals for focusing monochromators for X‐ray powder diffractometers are performed. The reflection power, avertences of crystal blocks, and radius of curvature of these crystals were determined by measuring rocking curves in dependence on the crystal position. The favourable application of curved graphite crystals as monochromators is shown by comparative X‐ray measurements of selected reflexes.