bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of shallow strain distributions in silicon single crystals with X‐ray bragg reflection
Authors: Zaumseil P. , Winter U. 
Published: January 2007

AbstractThe use of X‐ray double crystal diffractometry in Bragg case reflection for the determination of shallow strain distributions is investigated. Based on the theory of Takagi‐Taupin theoretical calculations of reflection curves of silicon crystals with diffusion induced strain profiles are carried out for different wave lengths and reflections. Possibilities for an optimal choise of reflections are discussed and the limits of detectibility are estimated. Experimental results of boron diffused silicon crystals confirm the theoretical results. Triple crystal diffractometry of (+n, –n, +n) setting is discussed as one possibility to increase the sensibility.
Polarization optics for X‐rays
Authors: Brümmer O. , Eisenschmidt Ch. , Höche H. R. 
Published: January 2007

AbstractAn experimental arrangement for X‐rays is described which is analogous to the optical bench for polarization investigations. Using this arrangement elliptically polarized X‐rays should be generated and proved. Although the dynamical theory of X‐ray diffraction is needed for X‐ray optics the polarization phenomena can be phenomenologically interpreted in analogy to visible light optics. The experimental results showed that with a wedge‐shaped crystal used as the phase shifter any polarization state of X‐rays can be generated.
Morphogenetic aspects of the LPE heterostructure growth: Time evolution of configuration entropy
Authors: Šrobár F. 
Published: January 2007

AbstractThe concept of the configuration entropy ΔSconf, introduced originally in the context of heterojunction superlattices, is extended to cover general one‐dimensional concentration profiles. Changes in ΔSconf as well as in its production rate Pconf = d ΔSconf/dt accompanying the growth of single and double AlxGa1–xAs based heterostructures are evaluated for a suitable set of relevant parameters. — ΔSconf is shown to increase monotonously during the growth process, while the — Pconf vs t dependences may exhibit sharp maxima and discontinuities in response to movements of the LPE apparatus slide. Given the fact that ΔSconf measures departure of the atomic population from the homogeneous (macroscopically structureless) equilibrium condition, such studies in effect monitor time distribution of the morphogenetic activity by the LPE growth processes.
On the influence of impurity additions and quenching temperature on the course of the microhardness (HV) during a two‐step ageing treatment of an Al‐2.0 at.%Zn‐1.3 at.%Mg Alloy
Authors: Gerlach R. , Löffler H. 
Published: January 2007

AbstractA pure as well as the analogous technical alloy were directly quenched from Tq = 400 °C or 490 °C to Ta, preaged at Ta (ranging between 50 °C and 160 °C) various times (ta), and subsequently postaged at R.T. up to tpost = 42 d.— Ageing the samples below the upper limit temperature of the homogeneous formation of G.P. zones (Thn) no essential difference in the course of the HV‐number attained after one‐ as well as two‐step ageing in dependence on the addition of impurity atoms and Tq could be found.— Contrary to this behaviour after pre‐ageing at Ta > Thn and postageing at R.T. a variation of both Tq and the content of impurity atoms shows a considerable effect. The reason is the difference in the density of nucleation sites for heterogeneous formation of precipitates of the η′‐ and/or η‐phase in dependence of Tq and impurity content.
”︁Four‐fold„ refringence in quartz
Authors: Semenchenko † V. K. , Bodnar I. T. , Isupov V. A. 
Published: January 2007

AbstractAn attempt is made to interprete the simultaneous existence of four refractive indexes (two ordinary and two extraordinary) near the α—β phase transition in quartz from the optical point of view. The theory of thermodynamical stability predicts the appearance of fluctuation areas of the α‐ and β‐phases in the vicinity of the α—β transition. On the basis of this theory the formation of infinite clusters, consisting of the merged fluctuation ranges, is assumed.
Crystal destruction of zeolite NaA during ion exchange with magnesium and calcium ions
Authors: Lutz W. , Fahlke B. , Lohse U. , Bülow M. , Richter‐Mendau J. 
Published: January 2007

AbstractExtreme conditions of ion exchange like, for instance, highly concentrated solution, high temperature and a long time of exchange can cause destructions of crystals. Zeolites NaMgA are structurally degraded much more than zeolites NaCaA. Reason for the reduced stability of crystals in presence of alkaline earth ions is the proton concentration increased beyond the dissociation equilibrium of water owing to the formation of weakly dissociated alkaline earth ion hydroxides. The zeolite lattice is destroyed hydrolytically by the influence of protons.
Studies on induced smectic phases (III). Fourier transform infrared and laser‐raman spectral differences between isotropic and induced smectic phase of binary mixtures of nematogens with contrasting dielectric anisotropies
Authors: Szabon J. , Pilz W. , Koswig H. D. 
Published: January 2007

AbstractThe SE, SB, SA induced phase sequence was detected in binary mixtures of two nematogens, 4,4′‐di‐n‐heptyl azobenzene (7AB) with 4‐n‐pentyl‐4′‐cyano biphenyl (5CB). The mixtures as well as the single components were studied by Fourier transform IR and laser‐Raman spectroscopy at different temperatures. Charge redistribution of 5CB is demonstrated by the spectral differences found by the ratio‐recorded IR spectra and also by integrating the intensities of some Raman lines. The spectra of the different phases of the 7AB—5CB mixture, built up from components of different length, indicate a population increase of the gauche conformers of 7AB in the smectic A phase.
The precipitation of alkaline‐earth metal polymetaphosphate hydrate powders from aqueous solution. Nucleation and crystal growth processes, final precipitate compositions and crystal sizes
Authors: Packter A. , Doherty W. O. S. 
Published: January 2007

AbstractThe precipitation of barium, strontium, calcium and magnesium polymetaphosphate hydrates was studied from aqueous solutions of initial metal salt concentrations from 0.001 to 3 M at 20 °C; equivalent sodium polymetaphosphate solutions were added to the alkaline‐earth metal chloride solutions. Precipitate compositions were determined by chemical analysis, paper chromatography, potentiometric analysis, thermogravimetric and differential thermal analysis and infra‐red spectrophotometry; final crystallite morphologies and sizes were studied by scanning electron microscopy and X‐ray powder diffraction.Nucleation rates and nucleus numbers (at the end of the induction periods) were very high; crystal numbers varied from 1014 to 1015 at the critical concentrations to above 1017 per 1. solution.Crystal growth rates were also very high and varied as the fourth power of the initial metal salt concentration. High molecular‐weight metal polymetaphosphate hydrates were precipitated from the more dilute solutions (0.001 to 0.025 M) while increasing amounts of the more soluble intermediate and low molecular‐weight products were precipitated from the more concentrated solutions. Washing with cold water removed the tri‐ and tetralinear and cyclic phosphate products. The magnesium salts were not precipitated even from 3 M aqueous solutions.The precipitates from aqueous (NaPO3(I))n (n = 12) solutions had the compositions (BaP2O6 · 2.5 H2O)6, (SrP2O6 · 3 H2O)n and (CaP2O6 · 4 H2O)n while the magnesium salt precipitate from 20 percent aqueous acetone solution had the composition (MgP2O6 · 4 H2O)n, the precipitate n values varied from 19 to 13. The precipitates from aqueous (NaPO3(II))n (n = 20) solutions contained 0.5n to n additional adsorbed water molecules; these precipitate n values varied in turn from 40 to 26.The final precipitate powders consisted of ‘spherules’ of highly microcrystalline or amorphous polymer glass; the spherule diameters were about 0.2 μm at the critical concentrations and decreased to below 0.05 μm with increasing solution concentrations.
Structural phase transitions in the LaMnO3+λ system
Authors: Bogush A. K. , Pavlov V. I. , Balyko L. V. 
Published: January 2007

AbstractStructural phase transitions in the LaMnO3+λ system are studied at various temperatures and with different Mn4+ ion concentrations. Two structural phase transitions are established. The O′‐orthorhombic – O‐orthorhombic transition (O′O transition) is due to removing the cooperative Jahn‐Teller distortions and occurs in the Mn4+ concentration range from 10 to 14% at room temperature. The temperature of this transition varies from 710 K for the stoichiometric LaMnO3 to room temperature for LaMnO3.07. The O‐orthorhombic – rhombohedral transition (OR transition) is due to the change of the rotation axis of the undistorted MnO6 octahedra from [100] and [110] to [111]. The temperature of this transition varies from 1010 K for LaMnO3 to 230 K for LaMnO3.135. The structural phase diagram of temperature vs composition is plotted, indicating the existence of regions of the phase with different structures.
Crack temperature rise due to crack propagation in visco‐plastic materials
Authors: Michel B. , Gründemann H. 
Published: January 2007

AbstractAn attempt is made to simulate the temperature field connected with a propagating crack in a visco‐plastic material. The authors apply modern continuum thermodynamics of strain‐rate sensitive work‐hardening materials to describe heat dissipation, convection, and conduction phenomena connected with the temperature development in the near‐crack region. The powerful finite element technique has been used to solve the coupled thermomechanical system of field equations being highly non‐linear. The results are in a better agreement with experiments than those obtained by the classic uncoupled methods.
Temperature dependence of the tetragonal distortion in I–III–VI2 compounds
Authors: Neumann H. 
Published: January 2007

AbstractOn the basis of free energy considerations with anharmonic contributions included a model is developed for the temperature dependence of the tetragonal distortion Δ of the I–III–VI2 compounds. Agreement with experimental data can be only achieved if compounds with Δ < 0.05 and Δ > 0.05 are considered separately. It is suggested that this result is related to the structural order‐disorder behaviour of the I–III–VI2 compounds.
Thermoluminescence studies in KBrxI1–x mixed crystals
Authors: Veeresham P. , Rao U. V. Subba , Babu V. Hari 
Published: January 2007

AbstractThermoluminescence (TL) studies have been carried out in KBr, KI, and in different compositions of KBrxI1–x mixed crystals as a function of X‐irradiation time. The TL glow peaks have been analysed and the trap depths and frequency factors have been calculated for different compositions. The complex TL peaks observed in these crystals were isolated by using thermal cleaning technique. The various glow peaks observed in these crystals were attributed to native impurities, first stage and second stage colour centers and the results have been discussed.
Metallurgically grown Schottky junction in directionally solidified eutectic Ag–Si alloys
Authors: Arnold Michael , Frühauf Joachim , Schneider Helmut Günther 
Published: January 2007

AbstractMetallurgically grown M(metal)–S(semiconductor) phase boundaries in directionally solidified AgSi alloys were investigated relative to their behaviour as Schottky junctions. By the aid of point contacts I/V characteristics have been measured which correspond to these ones of Schottky diodes. The Si crystallites were proved to be n‐doped. Reverse breakdown voltages of 8 … 24 V are not incompatible with the purity of the used materials. In forward direction the value of diode factor n = 1.1 … 5 shows the existence of several current flow mechanisms. In order to be able to interpret the characteristics it is necessary to have exact information on the specific resistivity of the Si crystallites and on the content of grain boundaries and dislocations in silicon. Beyond that the complicated shape of Si crystallites prevents the necessary determination of the interface size.
AlxGa1–xAs/GaAs thin window concentrator solar cells by LPE plus vapour phase diffusion
Authors: Romero R. , Sulima O. V. 
Published: January 2007

AbstractZinc diffusion from the vapour phase on a previously grown LPE nAlxGa1–xAs/nGaAs sample is discussed for thin window concentrator solar cell manufacture. A high cell shunt resistance and a low series resistance are achieved together with improved optical parameters via an impressed electric field in the emitter. Dark current components are rather low and 21.8% conversion efficiency is measured at AM 1.3. When the photogenerated short circuit current density is 8 A · cm−2, the fill factor is 0.77 and open circuit voltage is 1140 mv.
Preparation and characterization of strontium formate dihydrate
Authors: Prieto A. C. , Gonzalez A. , Hernandez E. , Rull F. , de Saja J. A. 
Published: January 2007

AbstractLarge single crystals of strontium formate dihidrate of high opticalquality have been grown from aqueous solutions by slow cooling from 50 °C to 20 °C. A thermogravimetric study is carried out in order to study the kinetic parameters and associated mechanism of the dehydration process. Raman vibrational assignments and a qualitative description of the normal modes are proposed. Two non‐equivalent formate and water arrangements with different degrees of vibrational distortion are established.
Growth and dissolution of BaFCl crystals
Authors: Somaiah K. 
Published: January 2007

AbstractSingle crystals of BaFCl have been growth by flux technique using BaF2 and BaCl2. Etching with formic acid revealed dislocation etch pits on (001) cleavage faces of the crystals, at room temperature. The influence of etching parameters such as undersaturation, temperature and concentration of poison in the etchant is studied. Decreasing the undersaturation of formic acid by reducing the percentage of water and increasing the temperature of the etchant were found not to have any effect on the morphology of etch pits. However, as the CdCl2 poison concentration is gradually increased, the orientation of the pits change from 〈100〉 to 〈110〉 at high concentration.
Growth and selective etching studies on NaBrO3 crystals
Authors: Rao K. Kishan , Sirdeshmukh D. B. 
Published: January 2007

AbstractSurface studies on (111) faces of sodium bromate crystals grown from aqueous solution show the presence of growth steps. A new etchant consisting of a mixture of 8 parts of glacial acetic acid and 2 parts of formic acid, to which 3 mg/cc of cupric nitrate is added, reveals the dislocation sites on (111) faces of these crystals. The etching action on (111) and (111) faces is different. Different microhardness values are recorded on (111) and (111) faces of these crystals. The difference in etching action as well as in microhardness values on (111) and (111) faces is discussed.
Mechanical behaviour of magnesium oxide single crystals at temperatures from 196 to 2400 °C
Authors: Berezhkova G. V. , Perstnev P. P. , Turaeva N. R. , Batrakov N. A. 
Published: January 2007

AbstractThe stress — strain characteristics of MgO single crystals in compression are investigated in the temperature range from –196 °C to 2400 °C on samples of the same shape and size. It is shown that the stress — strain curves may be subdivided into three basic types, each of them corresponding to the definite temperature range. The work hardening rate at stage I is temperature independent and at stage II lineary decreases with temperature increase in overall temperature range where work hardening is observed. The high temperature maximum in the temperature dependence on the proportional limit is found which is not due to the effects of impurities. The effect of geometrical form of specimens on stress‐strain parameters and the local true strain distribution in compressed specimens have been studied.
Dendritic structures in gel grown Gypsum
Authors: Raju K. S. 
Published: January 2007

AbstractSparingly water soluble Calcium Sulphate dihydrate (Gypsum) single crystals are grown by gel method, derived from the highly soluble reactants, Calcium Chloride and ammonium sulphate. By the diffusion of 1M Calcium Chloride solution into Sodium metasilicate gel (Sp.gr: 1.06 gm Cm–3, pH ∼ 7.5), imbedded before setting, with varied amounts of weak acid (acetic acid) and 20 ml of 1M ammonium sulphate solution, dendritic structures are commonly observed in the gel at the interface, at a particular concentration of the acid. The needle shaped tabular crystals are also observed to grow at the greater depths in the gel.Dendrites are studied by optical, X‐ray diffraction and Infra‐red studies. It has been established that the dendrites are Calcium Sulphate dihydrate crystals formed probably due to the influence of soluble impurities (like calcium acetate, in the present case), when the rate of diffusion is fairly high and the twinning mechanism favoured. The implications are discussed.
Investigations on the HCl gas‐phase etching of differently doped and oriented gaas crystals
Authors: Dorshchand S. , Däweritz L. , Berger H. 
Published: January 2007

AbstractThe influence of the orientation and dopant on the dissolution of GaAs surfaces in H2–HCl gas mixtures has been investigated. For this purpose the etch rates, temperature regions of different etching behaviour and the corresponding activation energies were determined for temperatures ranging from 540 °C to 945 °C. The etch rate anisotropy is correlated with the three existing temperature regions of different dissolution mechanisms. The orientation‐dependent transition temperatures are influenced by the dopant and can be related to the thermodynamic data of the dopant.
Radiation hardening studies in KBr‐KI mixed crystals
Authors: Rao U. V. Subba , Veeresham P. , Babu V. Hari 
Published: January 2007

AbstractRadiation hardening studies have been made in KBr, KI and in different compositions of KBr‐KI mixed crystals, grown from melt by Kyropoulos technique. The irradiation hardness in mixed crystals is found to vary non‐linearly with composition, attaining a minimum value at intermediate compositions. Dislocation density measurements have shown a high concentration of dislocations and grain boundaries in mixed crystals as compared to end crystals. The results obtained on radiation hardening of mixed crystals were explained in terms of dislocations present in them.
Thermoluminescence and optical absorption studies of KBr crystals doped with ca2+
Authors: Veeresham P. , Reddy K. Narasimha , Rao U. V. Subba , Babu V. Hari 
Published: January 2007

AbstractThermoluminescence studies of KBr crystals doped with 0.5 mole % of Ca2+ both in the ‘as‐grown’ state and after quenching them from various elevated temperatures indicate that the position of the glow peak which has been assigned to F‐centers is found to depend upon the state of dispersion of impurity. Bleaching of the X‐irradiated samples result in an additional peak and this has been attributed to Z1‐centers. Optical absorption measurements also confirm the formation of Z1‐centers in Ca2+ doped KBr crystals.
Effect of change of state of aggregation of impurity on tl and microhardness of KClxBr1–x mixed crystals doped with Ca2+
Authors: Rao U. V. Subba , Veeresham P. , Reddy K. Narasimha , Babu V. Hari 
Published: January 2007

AbstractMicrohardness and Thermoluminescence (TL) measurements have been made in KClxBr1–x mixed crystals doped with Ca2+ impurity. The variation of hardness in undoped and Ca2+ doped KClxBr1–x crystals with quenching temperature is investigated. TL studied of KClxBr1–x crystals doped with Ca2+, both in as‐grown state and after quenching them from various elevated temperatures indicate that the positions of the glow peak which has been attributed to F‐centers is found to depend upon the state of dispersion of impurity.
Doping process control in silicon epitaxy (II). Calculation of optimum control
Authors: Valkó P. , Kósza G. , Richter F. 
Published: January 2007

AbstractA procedure is developed to obtain desired dopant profile in epitaxial layer growth. Based an the results of system identification, linear‐quadratic optimal control theory is used to determine the optimal input PH3 concentration as a function of time. In the performance index an auxiliary weighting coefficient must be incorporated. It is discussed how to select this weighting coefficient.
Effect of oxygen impurities on recombination luminiscence in some alkali halide crystals
Authors: Cywińaski R. , Damm J. Z. 
Published: January 2007

AbstractThe low‐energy emission spectra of nominally pure NaCl, KCl, KBr, and KI crystals are examined at different electron beam densities and at temperatures between 80 and 300 K. The results obtained for the crystals of the same chemical formula but with different OH− contents, or subjected to the action of the air atmosphere, show that the emission bands considered are related with the presence of oxygen ions formed during radiolysis of such impurities like OH− or H2O. The decay of pertinent emission observed at higher radiation doses is explained by the transformation of simple oxygen ions into the neutral, inactive O2‐molecules.
Low temperature TL glow curves in KBrxI1‐x mixed crystals
Authors: Veeresham P. , Subba Rao U. V. , Hari Babu V. 
Published: January 2007

AbstractThermoluminescence (TL) glow curves were recorded in KBr, KI and in different compositions of KBrxI1‐x mixed crystals at LNT. For this a cryostat has been designed and fabricated. The glow peaks observed in these crystals have been attributed to differnent colour centers.
Low‐temperature anomalies in the plastic response of crystalline materials
Authors: Feltham P. , Butt M. Z. 
Published: January 2007

AbstractThe non‐uniform, wavy, temperature‐dependence of the yield‐stress and of the rate of logarithmic creep frequently observed in metals, alloys and non‐metallic crystalline solids at low temperature, is shown to be largely a consequence of the progressive inhibition of dynamic recovery processes as T → 0 K. Plastic deformation becomes increasingly localised, resulting in high stress‐concentrations. On allowing for this increase in the usual equations of the deformation kineties, the anomalies are very well accounted for.
Concentration dependence of the critical resolved shear stress of Cd‐Zn single crystals in the temperature interval 1.5 K—50 K
Authors: Navrátil V. , Hamerský M. 
Published: January 2007

AbstractCd—Zn single crystals were deformed in creep at temperatures between 1.5 K and 50 K. The from the creep experiments established critical resolved shear stress (CRSS) increases with cn where c is the atomic concentration of zinc as solute. The exponent n was found to be close to 2/3, i.e. the concentration dependence of the CRSS can be explained according to the theory of LABUSCH.
A new Iodide method for the preparation of II‐VI and IV‐VI compounds
Authors: Karagiozov L. , Trifonova E. P. 
Published: January 2007

AbstractA low‐temperature method for II‐VI and IV‐VI chalcogenides is proposed, based on the reaction of the iodide of group IIB or IVA element with the element of group VIA, in a flow reactor. The dependence of the electrical parameters of PbTe on technology conditions is investigated.
Study of the vibrational spectra of Natural Skolecite
Authors: Pechar F. 
Published: January 2007

AbstractThe vibrational spectra of the natural zeolite skolecite (locality Teigarhorn, Island) were measured in the infrared (200–4000 cm−1) and the far‐infrared (40–400 cm−1) regions; the infrared reflectance (200–1400 cm−1) and Raman scattering (50–4000 cm−1) spectra of the polycrystalline material were also measured. The KKK‐1 program (KROUPA, PELZELT) was used to calculate the dispersion curves of the optical constants. The bands in the spectra can be assigned to the vibrations of the individual bonds and structural groups of the skolecite on the basis of the literature data.