bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deformation‐induced After‐Glow in [(C2H5)4N]2MnBr4 Crystals
Authors: Chandra B. P. , Deshmukh N. G. , Sahu R. B. , Verma A. K. 
Published: January 2007

AbstractThe mechanoluminescence appears in [(C2H5)4N]2MnBr4 crystals even after their mechanical deformation. During the excitation of mechanoluminescence by the impact of a piston on to the crystals, the peak corresponding to the mechanoluminescence intensity versus time curve and the total intensity of mechanoluminescence increase with the impact velocity and decrease with the temperature of the crystals. It seems that the electric field produced during the inpact of the piston on to the crystal may perturb the ground and excited states of the molecules comprising the crystals. Thus the mechanoluminescence may follow the rate of compression during the deformation of the crystal and it may decay with the decay rate of phosphorescence after the compression. The mechanoluminescence and high pressure photoluminescence spectra are also reported.
The distribution coefficient of zinc during the crystallization of GaP from nonstoichiometric gallium melts
Authors: Koi H. , Buhrig E. , Hein K. 
Published: January 2007

AbstractExperiments were carried out to calculate by defining equations the distribution coefficient of zinc during the crystallization of GaP from the nonstoichiometric gallium melt. The TGS technique was applied to grow the crystals. Zinc detection was performed by the use of the radionuclide Zn65 as a tracer. The distribution coefficient being of the order of 0.1 is dependent upon temperature and concentration. These relations are demonstrated by plots and discussed with special respect to the literature data.
Growth of NaA zeolites in the presence of triethanolamine (TEA). The influence of water, TEA and Al contents
Authors: Schmitz W. , Kornatowski J. , Finger G. 
Published: January 2007

AbstractIn order to obtain larger NaA zeolite crystals, the influence of starting materials and preparation conditions on the crystal growth has been studied. It is shown that the growth of NaA is most sensitive to changes in the gel composition. The crystal sizes are limited by subsequent nucleation occurring during the crystallization process. At the optimum gel composition, it is possible to grow crystals up to 75 μm in 100–400 ml reactants.
Liquid phase epitaxy of SiC in the system TbSiSiC by temperature gradient zone melting (III). Epitaxial layer properties
Authors: Peev N. S. , Tairov Yu. M. , Smirnova N. A. , Kalnin A. A. 
Published: January 2007

AbstractIn the present work the electrophysical and structural properties of the SiC epitaxial layers grown by the temperature gradient zone melting method in vacuum conditions is considered. Some correlations between the epitaxial layer properties and the process conditions are observed. It is shown that the performence of the growth process in vacuum leads to a significant improvement of the layer quality, if one observes some requirements – how to decrease significantly the number of the second phase inclusions and how to improve the structural perfection of the layers.
Growth kinetics, structure and surface morphology of AlN/α‐Al2O3 epitaxial layers
Authors: Bugge F. , Efimov A. N. , Pichugin I. G. , Tsaregorodtsev A. M. , Chernov M. A. 
Published: January 2007

AbstractThe gas‐phase epitaxy of AlN on saphire substrates in the system AlHClNH3–Ar was investigated. The uniformity and structural perfection of the layers were shown to be determined by gas dynamics in the growth zone. The growth rate of AlN‐layer is proportional to AlCl concentration in the growth zone and does not depend on NH3 partial pressure. This is in accordance with the law of diffusional stoichiometry.The morphology of AlN‐layers was shown to be dependent on the growth rate and the substrate orientation. Smooth mirror‐like layers were prepared on the sapphire planes (0001) and (1120) at low growth rates.X‐ray microanalysis showed the oxygen impurity content at the level 1 — 5 · 1021 cm−3. Other impurities were not available.
Electrical conductivity and crystal structure of pure and SrCO3‐doped Na2CO3
Authors: Guth U. , Barwisch F. , Wulff H. , Schmidt P. , Möbius H.‐H. 
Published: January 2007

AbstractThe electrical conductivity of pure and SrCO3‐doped sodium carbonate has been measured in the temperature range 310–800 °C in air using a dc technique. Its concentration dependency is similar to that of the K2CO3–SrCO3 system described recently (GUTH et al. 1986). The maximum conductivity could be observed at ≈ 20 mol.% SrCO3. At temperatures > 440 °C, the conductivity of Na2CO3–SrCO3 mixtures containing up to 80 mol.% SrCO3 is larger than that of pure Na2CO3. X‐ray investigations of slowly cooled samples show the mixtures to be heterogeneous. X‐ray diffraction patterns of quenched mixtures containing 10 mol.% SrCO3 show reflexes of a high temperature compound. SrCO3, however, could not be detected. The lattice constants of this hexagonal compound Na2Sr4(CO3)5 which is isotyp with Na2Ca2Sr2(CO3)5 described by CHEN and CHAO are a0 = (1066.1 ± 0.4) pm and c0 = (653.2 ± 0.2) pm.
High‐temperature annealing stages in irradiated imperfect crystals
Authors: Larikov L. N. , Borimskaya S. T. 
Published: January 2007

AbstractThe effect of neutron irradiation on the structure of crystals with different dislocation densities and types of crystal lattice and on subsequent high‐temperature annealing is studied. The extent of this effect is determined by the substructure of irradiated material. The processes responsible for stage V and VI annealing of radiation‐induced defects are investigated by quantitative X‐ray diffraction topography and two‐crystal spectrometer technique. A retarding effect of neutron irradiation on all the stages of recrystallization is established enabling the temperature range of application of hardened metal and alloys to be shifted to higher temperatures.
Kinetics of crystallization of potassium chloride from aqueous solutions at 30 °C
Authors: König Ax. , Emons H.‐H. 
Published: January 2007

AbstractThe aim of this work is to use a diffusion layer model for the determination of individual rate constants of reaction and diffusion step of KCl at 30 °C. Crystal growth rate was measured by travelling microscope technique. From the measured values of the mean linear growth rate the resulting individual rate constants and the effectiveness factors (GARSIDE) are evaluated as a function of the driving force and of the flow velocity of solution. The significance of diffusional and surface reaction resistances against mass transfer is discussed in relation to the experimental conditions used.
Tracing of dislocations in ammonium hydrogen tartrate single crystals
Authors: Desai C. C. , Hanchinal A. N. 
Published: January 2007

AbstractSparingly soluble ammonium hydrogen tartrate (AHT) crystals are grown by the gel method, derived from the diffusion of ammonium chloride into the set gel containing tartaric acid. Crystals up to 23 × 5 × 3 mm3 in size are grown at room temperature. AHT crystals are cleaved along (010) planes and the cleavage surfaces are studied by using multiple beam interferometry. The interferograms have revealed that the cleavages are quite flat. An attempt is made to trace the trajectory of dislocations of isolated as well as matched pairs of (010) cleavages of AHT when etched in a mixture of formic acid and methyl alcohol (2:1) and 1.0 M SrCl2 solutions. Optical and transmission electron micrographs of dislocations show oblique, parallel and continuous line characteristics. Rows of equally spaced dislocation pits are observed and the implications of this are discussed.
Probability analysis of the azimuthal distribution of glide traces on the surface of plastically deformed polycrystalline metals
Authors: Preuss Heinz H. W. 
Published: January 2007

AbstractWith the simple assumption of an isotropic distribution of grain‐orientation (absence of texture) and independent plastic deformation of the grains, when by increasing load some constant limit of the resolved shear stress is reached for any slip system within the grain, one can find the azimutal distribution of glide traces on the free surface of the material by crystallgeometrical probability analysis. The azimutal distribution is independent on crystal symmetry and is characterised by a gap symmetrically arranged around the stress direction and by a flat minimum perpendicular to the stress direction. The height of the minimum does not depend upon the level of stress but is nearly a linear function of the real local plastic deformation as a consequence of developing texture.
The crystal structure of nematogenic 2‐bromo‐1,4‐phenylenediyl bis(trans‐4‐n‐propylcyclohexanoate) — a special kind of disorder
Authors: Hartung H. , Winter G. 
Published: January 2007

AbstractThe title compound with the formula C3H7–C6H10–COO–C6H3BrOOCC6H10C3H7 (BPBPC) crystallizes in a triclinic unit cell with dimensions a = 5.822(2), b = 8.732(3), c = 13.016(5) Å, α = 94.42(3)°, β = 93.47(3)°, γ = 104.85(2)° containing one molecule. The structure has been solved by heavy atom method and refined to R = 0.083.The BPBPC molecules adopt an optimum stretched form and exhibit pseudo‐centrosymmetry in consequence of a special kind of disorder within the crystal lattice.
Microhardness of tetrahedrally bonded elemental and binary semiconductors
Authors: Neumann H. 
Published: January 2007

AbstractAn analysis of experimental microhardness data shows that the microhardness at room temperature of the diamond, zincblende and wurtzite structure compounds follows the simple relation H = hoa−xTm(1 –gofi) where a is the lattice parameter Tm the melting temperature, fi the spectroscopically defined bond ionicity and ho, x, and go are constants having the same values for all compounds. The close relation between microhardness and bulk modulus is discussed.
The influence of natural convection on the mass transfer kinetics in LPE growth
Authors: Nghi Nguyen Thanh , Khang Dao Duc , Tuan Duong Anh , Nghia Nguyen Xuan , Hai Nguyen Thi Qui 
Published: January 2007

AbstractThe simplified scheme has been suggested for quantitative estimation of the effect of natural convection on the LPE layers thickness while growing from a finite solution with parallel horizontal and vertical substrates. The convective‐diffusive mass transfer model is being developed on the base of boundary layer approximation. In the case of horizontal growth the layer thickness is determined by effective solution thickness which is distinguished for an upper and lower substrate and depends on convection intensity. For the vertical growth system the expression describing the variation of layer thickness along the substrate has been obtained and the vertical temperature gradient necessary for eliminating a wedge shaped growth in this case is calculated.The experimental investigations of LPE growth of GaP layers from finite solution with horizontal and vertical substrates are carried out. The thickness and shape of LPE layers obtained in both cases coincide well with results of calculation.
Continuous magnesium hydroxide precipitation
Authors: Dobrescu V. , Păraşcu E. , Pincovschi E. 
Published: January 2007

AbstractThe main kinetic parameters of the precipitation process of magnesium hydroxide from magnesium nitrate have been determined. By using gaseous ammonia as precipitation agent in a 20% stoichiometric excess and in a reactor residence period of 30–60 min we determined the total kinetic order of the process, which is 2.67. For a 50 min residence time, we determined the filtration and washing parameters for the magnesium hydroxide obtained from the beginning of the precipitation process till a stationary state was reached.
The precipitation of iron (II) and nickel oxalates with alkaline‐earth metal oxalates: Induction periods, nucleation rates and mechanisms
Authors: Packter A. , Chauhan P. , Omomo A. 
Published: January 2007

AbstractThe coprecipitations of magnesium (and barium) iron(II) and nickel oxalate dihydrates were studied from excess magnesium and barium oxalate solutions. Nucleation rates were estimated from the induction periods for the coprecipitations. The nucleation rates in excess magnesium oxalate solutions first decreased with increasing excess oxalate anion concentration to minimum values and then increased with increasing magnesium cation concentration. At low to intermediate Mg/Fe(II) (and Mg/Ni) ratios the main nuclei were FeOx (and NiOx); at intermediate Mg/Fe(II) (and Mg/Ni) ratios the main nuclei were probably MgOxFeOx (and MgOxNiOx) mixtures and/or solid solutions of compositions MgαFe1αOx (and MgαNi1αOx); at high Mg/Fe(II) (and Mg/Ni) ratios the main nuclei were MgOx.The nucleation rates in excess barium oxalate solutions were similar to those for the precipitation of barium oxalate from supersaturated equivalent solutions. The main nuclei in most systems were BaOx.
An analysis of the applicability of the Scheil equation in the determination of segregation in monocrystals of the manganese‐zinc ferrites Mn1xZnxFe2O4
Authors: Wołczyński W. , Guzik E. 
Published: January 2007

AbstractTheoretical assumptions concerning the segregation phenomenon of alloying components during formation of monocrystals of the manganese‐zinc ferrite Mn1xZnxFe2O4 have been presented. Taking into account the case of the unidirectional solidification of the above ferrite by means of the Bridgman furnace, which is working in:

Closed system.
Open system, with adding of the pure component (melting at an elevated temperature).
Open system, with adding of ferrite of a nominal composition.
The method for calculation of alloying components segregation has been analysed. A possibility of modelling the segregation by means of the choice of the size of the melting zone has been considered for a given monocrystal.
The crystal and molecular structure of 2,6,11‐tribromo‐14‐oxabicyclo[8.3.1]tetradec‐6(E)‐ene – A transannular O‐heterocyclization product of a thirteen membered triene
Authors: Sieler J. , Richter R. , Haufe G. , Faure R. 
Published: January 2007

AbstractThe crystal structure of the title compound has been determined from single‐crystal X‐ray diffractometer data collected with a CAD‐4 diffractometer. C13H19OBr3 crystallizes in space group Pbca with a = 24.005(6) Å, b = 12.038(4) Å, c = 10.397(2) Å and Z = 8. Leastsquares refinement gave an R value of R = 0.057 for 1072 observed reflections I > 3σ(I). The investigated product is a bicyclic tetrahydropyran compound with a vinylic bromine atom.
Molecular geometry and tautomerism of 2‐carboxymethylamido‐3(4H)‐quinoxalone
Authors: Pfeiffer D. , Scharfenberg P. , Reck G. 
Published: January 2007

Abstract2‐Carboxymethylamido‐3(4H)‐quinoxalone cyrstallizes in the triclinic space group P1 with four molecules per unit cell (a = 8.797, b = 11.240, c = 11.099 Å, α = 85.62, β = 67.75, γ = 67.35°). The structure was solved by direct methods and refined by fullmatrix least squares calculations to the final R‐value of 0.042.The tautomeric equilibrium of the compound is discussed in connection with the molecular conformation and the ability to form intramolecular hydrogen bonds. Evidence is given that the oxo form of 2‐hydroxyquinoxalines largely dominates and that 5‐membered intramolecular chelates involving H‐bonds of the type (N, O)H…(N, O) are so weak that they usually do not govern conformational equilibria.
The properties of application of the electron probe X‐ray microanalysis in the high‐temperature range particularly for the study of diffusion processes and phase formations
Authors: Däbritz S. , Ullrich H.‐J. , Kleinstück K. 
Published: January 2007

AbstractIn this study the efficiency of a manufactored heating stage for the electron probe microanalyzer is presented and a methodology (High‐Temperature Electron Probe X‐Ray Micro Analysis, HT‐EPXMA seldom used till now for the determination of diffusion coefficients and activation energies, for the discovery, observation and characterization of phases in the heating‐up process as well as for the investigation of crystallographic parameters of phase transformations is obtained.
Electrooptic behaviour of a nematic MBBA layer with a thick interfacial surfactant layer
Authors: Hinov H. P. 
Published: January 2007

AbstractThe electro‐optic behaviour of MBBA nematic layers with various surfactants added of anionic, cationic, zwitterionic and non‐ionic character and a considerable amount (2wt% to 8 wt%) was studied. The formation of surface‐induced flexoelectric domains in all cases clearly showed that the anchoring of the liquid crystal layers has been weak. Such a weak anchoring can be explained with the formation of a perioidc (in the most simple case sinusoidal) MBBA‐surfactant interface boundary with a mutual penetration of the liquid crystal and surfactant molecules with some gradient.
On the position of the upper limit temperature of homogeneous nucleation of precipitates in low concentrated AlZn alloys
Authors: Wendrock G. , Löffler H. , Raphelt I. , Truong Chu Thien 
Published: January 2007

AbstractThe upper limit temperature Thn of the onset of homogeneous nucleation of Guinier‐Preston (GP) zones was determined for three AlZn alloys with xZn = 4.5, 6.0 and 8.0 at.% by SAXS investigations (cooling from the range of homogeneity to various temperatures Ta and ageing at Ta). The results are Thn = (95 ± 3) °C for xZn = 4.5 at.%, (118 ± 3) °C (6.0 at.%) and (154 ± 3) °C (8.0 at.%), respectively. The obtained results fit well the data known for the alloys with higher contents of Zn.It is stressed that one has to distinguish between Thn, determined by isothermal measurements after a direct quench or cooling to the respective Ta, and the upper limit temperature Trhn of the onset of the rapid homogeneous nucleation of GP zones (continuous cooling).
Deformation stages in a stabilized loading cycle of fatigued FCC metals(II). Discussion and conclusions
Authors: Holste C. , Kleinert W. , Fischer W. 
Published: January 2007

AbstractConsidering the experimental results presented in Part I of this work and taking into account the nature of the deformation mechanisms during cycling, four deformation stages are assumed to exist in a stabilized loading cycle. The mechanical behaviour in the stages is discussed on different structure levels. In particular, it is shown that the heterogeneous plastic deformation caused by different local yield stresses in the dislocation‐dense and dislocation‐poor regions of the material seems to be limited to a relatively small interval of plastic strain εp (10−4 ≦ εp ≦ 10−3).
Computer simulation of the pyramidal and prismatic growth of KDP‐type crystals
Authors: Bernhardt Hj. 
Published: January 2007

AbstractThe growth of KDP crystals dependent on the applied physical parameters as seed sizes pH‐value of the solution, rate of the temperature decrease and initial supersaturation has been investigated. The prismatic and pyramidal growth components have been investigated separately. A pragmatic model which is hold as simple as possible simulates numerically different shapes of the growth habit, which are caused to the variation of aforementioned parameters. The results are plotted quasigraphically. The observed shapes of the simulated habit enable us to understand some growth striations in real crystals. The time dependent behaviour of the growth velocity may be simulated, additionally.
Measurement of optical biaxiality and tilt angle in A smectic c liquid crystal
Authors: Schmiedel H. , Frieser A. 
Published: January 2007

AbstractWe present a new method of measuring the tilt angle and the optical biaxiality in liquid crystals (LCs). The method uses a fitting procedure of the optical path difference in specially prepared LC cells. Measurements are performed in the SC phase of 4‐n‐hexyloxyphenyl‐4n‐decyloxybenzoate (HOPDOB) by means of microscopic observations in a rotary heating stage.
Measurement of particle size and internal strain in doped tungsten powder by X‐ray methods
Authors: Salewski W. 
Published: January 2007

AbstractIn the powder metallurgical process of tungsten wire fabrication for incandescent lamps the stepwise reduction of tungsten oxides (WO3 or W20O58) plays an important role in respect to the efficiency of doping elements (especially potassium) for the formation of the non sag structure of tungsten wires. The influence of temperature and time in the reduction steps has been investigated by means of the X‐ray method for determination of particle size and internal strain described by KOCHENDOERFER. It has been founded a close relationship between the internal structure of metal powder (especially internal strain) and the potassium content as well as the sintering behaviour of these powders. – The KOCHENDOERFER method is a usefull tool for the improvement of reduction parameters in regard to the sintering behaviour.
Characterization of chemical perfection of YAG:Nd crystals with absorption spectroscopic methods
Authors: Bernhardt Hj. , Rauch R. , Toepfer K. , Wehrhan G. 
Published: January 2007

AbstractThe absorption constants of Neodymium in YAG are determined at the absorption lines 434.4 nm; 588.6 nm; 868 nm and compared with literature data. The influence of measuring parameters is discussed. The calibration of the concentration is made absorptionspectrophotometrically by comparison of chemically decomposed solutions of YAG crystals with solutions of mixtures Y2O3/Al2O3/Nd2O3.The measurement of the near‐edge absorption is shown to be a practical method for characterization of stoichiometric composition of Nd: YAG crystals.
Sensivity of the thermal gradient flotation method
Authors: Andreev G. A. , Hartmanová M. 
Published: January 2007

AbstractThe theoretical sensitivity of the flotation method of density determination has been estimated. The natural pressure gradient is found to be a limiting factor and the maximum sensitivity is 3 × 10−9. In practice, the accuracy of the flotation measurements is controlled by the sample error. The main sources of sample errors have been analysed.
Phase transition studies in the liquid crystal p‐cyanophenyl trans‐4‐propylcyclohexane carboxylate
Authors: Venkatacharyulu P. , Gupta A. V. N. , Rao L. V. 
Published: January 2007

AbstractThe specific volume and ultrasonic velocity measurements (at four different fixed frequencies) are carried out in the liquid crystal p‐cyanophenyl trans‐4‐propylcyclohexane carboxylate. From these studies various physical parameters like adiabatic compressibility, molar sound velocity, molar compressibility, Van der Waals' constant and intermolecular free lengths are derived. The variation of the order parameter with temperature at the four fixed frequencies is also studied. The results are discussed.
The current understanding of epitaxial CVD silicon doping in the light of modelling and theory development (III). The law of epitaxial layer doping and its limitation
Authors: Kühne H. 
Published: January 2007

AbstractVarious doping mechanisms discussed in recent literature are applied to the theoretical concept derived in the previously published Part II of the paper, whereby a variety of hypothetical laws of dopant incorporation is revealed. Those laws cannot be distinguished from each other by doping experiments, but are testable, at least in principle. When substituting three doping‐process‐relevant empirical constants, all of them might be changed into that single empirical, but theory‐aided model equation, which enables apitaxial layer doping to be described as a result of intended variations of the main process parameters: partial pressure of the dopant source, layer growth rate, total pressure, and deposition temperature.
On the origin of the (1216)‐orientation in epitaxial AIN layers on R‐plane sapphire
Authors: Georgi Ch. 
Published: January 2007

AbstractEpitaxial AIN grown by MOCVD on (0112)Al2O3 substrates usually is (1210)‐oriented. Here for the first time (1216)AIN was found in MOCVD layers. This AIN orientation is known from other growth techniques, its origin is generally not understood. An explanation is given based on twinning in the early growth stages which is also applicable to the growth of (1216)ZnO on (0112)Al2O3.