bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermoluminescence and optical absorption studies in γ‐irradiated KClxBr1–x mixed crystals
Authors: Veeresham P. , Reddy K. Narasimha , Rao U. V. Subba , Babu V. Hari 
Published: January 2007

AbstractThermoluminescence (TL) and optical absorption measurements have been carried in γ‐irradiated KCl, KBr and various compositions of KClxBr1–x mixed crystals as a function of irradiation time and composition. The position of the main glow peak (high temperature peak) and F‐band position are found to vary non‐linearly with composition, showing a correlation between colour centers and TL. The TL peaks have been analysed by numerical fitting and the trap depths and frequency factors have been calculated for different compositions of the mixed crystals. The thermal ionisation energy of F‐centers has been calculated for the mixed crystals and it is found to vary non‐linearly with composition. The results obtained in mixed crystals have been discussed in terms of high disorder present in them.
Phase fronts at the NaNbO3P‐⇌ NaNbO3 R phase transition
Authors: Dec J. 
Published: January 2007

AbstractThe structural phase transition between phase P and phase R in NaNbO3 single crystals was studied by an optical method. It was found that this transition is similar to the martensitic transformation and that the phase fronts are formed by crystallographic planes having indices close to {0.2.11}. Behind the simple phase front a monodomain state arises. The polydomain state is the resultant of complex phase fronts.
Growth, intensity and probabilities of f‐f transitions of Nd3+ ions in KNd(PO3)4 single crystals
Authors: Mazurak Z. , Jeżowska‐Trzebiatkowska B. , Schultze D. , Waligora C. 
Published: January 2007

AbstractFrom a study of the melting diagram KPO3—KNdP4O12 optimum conditions are derived for the growth of KNd(PO3)4 single crystals by the flux method. The absorption spectrum of KNd(PO3)4 was measured between 320 and 1000 nm at room temperature. The three JUDD‐OFELT parameters Ωλ were determined by numcerical methods and compared to the data for NdP5O14. A correlation has been attempted between the Ω2 parameter and the site symmetry of Nd3+ in Nd‐containing laser crystals. The calculated fluorescence branching coefficients from the 4F3/2 level are in good agreement with the epxerimental data.
Structure of fault stackings of molecular layers X—M—X in CdI2 polytypic crystals
Authors: Pałosz B. , Przedmojski J. 
Published: January 2007

AbstractThe arrangements of molecular layers I—Cd—I, which may be regarded as “faulted” for CdI2 polytypic crystals, are analyzed. Tentative classification of faults into those which are intermediate structure between the basic polytypes 2H and 4H and faults occurring between different blocks of pure structure 4H is proposed. The connection between some growth parameters and the structure of faults in CdI2 crystals grown from solutions is discussed. It is shown that the geometrical classification of stacking faults used for layered inorganic crystals is not appropriate for the description of the faults existing in polytypic crystals of MX2 type. The effect of weak external electric and magnetic fields on the polytypic structure of CdI2 is analyzed. The experiments performed for several hundred of polytypes of CdI2 showed that the external fields may, in some conditions, affect the organization of the polytypic structure of crystals very strongly. In particular, it was found that the external fields may change the period of polytype cells and that the relative number of hexagonal and rhombohedral polytypes differ very strongly for crystals grown in the absence and in the presence of external electric and magnetic fields.
X‐Ray study of the defect structure of PbTe single crystals
Authors: Berger H. , Mizera E. , Auleytner J. 
Published: January 2007

AbstractPbTe single crystals grown by different methods were thinned electrolytically and examined by X‐ray transmission topography. The transmission topographs, first obtained of this material, reveal substructure, slip lines and single dislocations. The samples exhibit different structural perfection in dependence on the growth method. In crystals of relatively high perfection, slip lines are the striking feature of defect structure, caused by surface damage during mechanical preparation. The most perfect sample has a dislocation density of 102 to 2 ṁ 103 cm−2. No slip occurs, probably due to small dopant contents.
Thermotropic liquid crystalline compounds with lateral long‐chain substituents (II).: Synthesis and liquid crystalline properties of 1,4‐Bis [4‐substituted‐benzoyloxy]‐2‐n‐alkylbenzenes
Authors: Weissflog W. , Demus D. 
Published: January 2007

AbstractWe synthesized 102 new 1,4‐bis‐[4‐subst.‐benzoyloxy]‐2‐n‐alkylbenzenes of the general formulamagnified imagewith R = alkyl, alkyloxy, alkanoyloxy, alkyloxycarbonyloxy and n = 0 to 16. Surprisingly all of the new compounds are liquid crystalline nematic. Thus it is proved that lateral long chain substituents are compatible with liquid crystalline properties.
Dielectric relaxation investigations of the isotropic and nematic phases of 4‐n‐Butyloxyphenyl‐4‐n‐hexylbenzoate (BOHB)
Authors: Kresse H. , Demus D. , Moscicki J. K. , Wrobel S. 
Published: January 2007

AbstractExperimental values of the complex dielectric permittivity in a wide frequency range are analized for the isotropic and nematic phase of BOHB. The results are discussed from the point of view of different of molecular reorientation mechanisms which are related to the structure of the molecule. It can be concluded that the molecules in the nematic phase exhibit a stronger tendency to reorient as “rigid bodies”.
The comparative study of mosaic structure of ZnO crystals by γ‐ray diffraction and conoscopic methods
Authors: Loshmanov A. A. , Chernysheva M. A. , Trunov V. A. , Kurbakov A. I. , Shaldin Yu. V. , Sizova N. L. , Kuzmina I. P. , Regel V. R. 
Published: January 2007

AbstractIt has been carried out the investigation of the mosaic structure of ZnO crystals by two methods providing the information on mosaic structure and inner stresses (γ‐ray diffraction and conoscopic method). It has been observed a certain correlation between the results obtained by the two methods.
Influence of the graduated composition region on the properties of GaInAs epitaxial layers grown on GaAs substrates
Authors: Popov A. , Ivanov I. 
Published: January 2007

AbstractThe electrical properties of Ga1‐xInxAs layers (0 < x < 0.3) are investigated. The layers are grown on <111> oriented GaAs substrates. A transition layer is grown with an increasing indium content to decrease the mismatch of the lattice parameters of the substrate and the final layer. A special many‐section crucible is used. In dependence on composition the decrease both of mobility and carrier concentration with the increase of compensation is observed. These facts are connected with the introducing of additional acceptors without donor concentration changes.
Correlation between different parameters of plastic deformation in doped NaCl crystals
Authors: Boyarskaya Yu. S. , Zhitaru R. P. , Linte M. A. 
Published: January 2007

AbstractThe yield stress (τy), the microhardness (H) and the dislocation mobility in the stress field of a concentrated load (γ) were measured in NaCl: Ca and NaCl: Pb single crystals within the temperature interval 77–673 K. It was shown that there was a good correlation between the concentration changes of τy, H and γ for NaCl:Ca crystals. Such clear results were absent for NaCl:Pb single crystals. An anomaly of τy at 77 K was revealed for these crystals; it was not followed by the H anomaly. In conclusion it was stated that the impurity hardening was connected with the increasing of dislocation mobility but such a parameter did not determine the temperature hardening.
Investigation on low temperature thermoluminescence centres in Quartz
Authors: Bernhardt Hj. 
Published: January 2007

AbstractThe present paper will help to understand the often investigated process of thermoluminescence of quartz which is of high complexity. A lot of traps exist in quartz crystals which compete with each other with respect to the trapping of charge carriers during the X‐ray treatment. That is why a variety of processes takes place after X‐irradiation at liquid nitrogen temperature (LNT) of quartz which complicate the phenomenology of low temperature thermoluminescence. This competition in the trapping process leads to the socalled “sensibilization” or “desensibilization” effects of thermoluminescence, respectively, which are described in this paper for the first time. This effect means the dependence of the LNT thermoluminescence intensity on a pre‐irradiation dose applied at room temperature (RT). The influence of this pre‐irradiation is understood assuming the saturation of competitive traps. This favours an enhanced trapping of charge carriers at LNT‐(shallow) traps instead of the preferential trapping on the deep traps in the case of X‐ray treatment of the as‐grown crystal at LNT. To get the afore mentioned model we take into account not only thermoluminescence but also coloration, ir‐ and vuv‐absorption measurements.
Chemical kinetics of dissolution of BaMoO4 crystals
Authors: Arora S. K. , Trivikrama Rao G. S. , Batra N. M. 
Published: January 2007

AbstractAn etchant capable of revealing the sites of dislocations in the flux‐grown crystals of BaMoO4 has been established. Using this etchant (HNO3), effect of etching time, acid concentration and temperature on the selective etch rate is demonstrated. It is established that the process of dissolution in unstirred HNO2 solutions is one of the diffusion rate controlled; an empirical equation governing the kinetics has been suggested.
Comparison of luminescence characteristics of Doped Molecular crystals grown by various methods
Authors: Kurnosov I. V. , Levitski I. A. , Naboikin Yu. V. 
Published: January 2007

AbstractThe effect of growth conditions on the line broadening in low temperature luminescence spectra of pyrene‐doped biphenyl single crystals in investigated. It has been shown that the crystals, grown by plate sublimation technique, possess the minimal linewidth. Various possible mechanisms of line broadening are discussed.
Auger electron spectroscopy studies of impurity effects on the hot deformability of AISI M2 high speed steel
Authors: Szilvásy Cs. , Menyhárd M. , Gergely G. 
Published: January 2007

AbstractThe effects of various materials parameters on hot deformability f of AISI M2 high speed steel are studied in a complex way. These studies revealed beside other parameters (e.g. carbides) a strong correlation between some impurities (S, Sn) and f, determined by hot deformability tests. The correlation between f and the P content prooved to be weaker. The paper is devoted to impurity effects. The composition and impurities of the samples and their isolated carbide phases have been determined by chemical analysis. In situ AES fractography and SEM were applied to study the fracture surfaces. The main results are: The S concentration of the fracture surfaces exhibits a correlation with the bulk content. Strong enrichment of S and P within a thin (1–3 nm) surface layer was revealed by AES in‐depth profiling, showing also carbide phases. In the temperature range ‐150°C — +250°C no grain boundary fracture was observed, fracture was ductile and void type. The fracture path is determined by carbides, being the sites of S and P enrichment.
Theoretical description of the external electroluminescence around a single dislocation oriented perpendicular to the surface
Authors: Pasemann L. , Hergert W. 
Published: January 2007

AbstractUnder the assumption that a dislocation decorated by impurities can be described as a macroscopic inhomogeneity the radial distribution of the flux of photons around a dislocation is calculated, where the internal absorption of the luminescence is taken into account in addition to the effect of the surface. The theoretical results are used to compute simulated images for different values of the radiative lifetime inside the dislocation region.
Dislocation generation around cylindrical pores
Authors: Friedrich E. , Boiko Ju. I. , Schatt W. 
Published: January 2007

AbstractThe formation of dislocation arrays reflecting the crystallographie symmetry of the surface pores formed by a mechanism of pitting corrosion was observed. The hypotheses developed in connection with the origination of dislocations around cylindrical pores by the effect of capillary forces led to process parameters whose estimated values agree well with those experimentally obtained. It is pointed to the importance of this process for the shrinkage during sintering.
Influence of lateral branches on the properties of liquid crystalline 1,4‐Bis‐[4‐n‐hexylbenzoyloxy]‐2‐subst.‐benzenes (II): connection between molecular structure and physical properties
Authors: Demus D. , Hauser A. , Selbmann Ch. , Weissflog W. 
Published: January 2007

AbstractIn 8 1,4‐bis‐[4‐n‐hexylbenzoyloxy]‐2‐subst.‐benzenes and one analogous hexylcyclohexanoyloxy compound the clearing temperatures, enthalpies, entropies, volumina and order parameters are considered with respect to the molecular structure and compared with predictions of molecular statistical theories. The results are in qualitative agreement with theoretical predictions and show the predominant role of the steric repulsive forces in stabilizing the nematic state.
Forest intersection of dislocations in HCP structures
Authors: Püschl W. , Schoeck G. 
Published: January 2007

AbstractThe contribution to flow stress by junction reactions in hep metals is computed using a virtual displacement method. Basal glide by 0°, 30°, 60° and 90° dislocations and trees with Burgers vector length a, c and |c + a| are considered. Conceptual shortcomings of previous treatments are discussed.
Precision measurements of plastic deformation of β‐CuZn at helium temperatures
Authors: Takeuchi S. , Hashimoto T. , Maeda K. 
Published: January 2007

AbstractBy attaching condenser plates directly to the tensile specimen, creep rates of β‐CuZn single crystals have been measured by the capacitance change in the strain‐rate range of 10−7to 10−5s−1and at temperatures between 0.7 and 17 K using a3He cryostat. Slope of the temperature variation of the stress to give a constant strain‐rate decreases below 5 K and seems to level off at 0 K. The strain‐rate sensitivity becomes almost constant below 2 K. The conventional activation analysis showed that an ARRHENIUStype strain‐rate equation breaks down drastically below 5 K. For an effective temperatureT*which gives 2 K at 0 K and asympototically coincides with the testing temperature at 5 K, the experimental results can be fitted to the ARRHENIUSstrain‐rate equation with an activation enthalpy ΔH(τ) for the PEIERLSmechanism. The above result is interpreted in terms of the quantum‐mechanical oscillation of the dislocations.
Deformation mechanism and dislocation structure of high‐purity molybdenum single crystals at low temperatures
Authors: Kaufmann H.‐J. , Luft A. , Schulze D. 
Published: January 2007

AbstractHigh purity molybdenum single crystals were deformed in tension and compression along the symmetric double slip orientation [110] in the temperature range from 300 K down to 0.5 K with strain rates between 10−3 and 10−5 s−1. The activation volume was measured by stress relaxation tests. The dislocation structure of the deformed crystals (T → 1.85 K) was examined by high voltage electron microscopy. It was established that the low temperature increase of the critical shear stress exhibits three distinct temperature regimes with different temperature dependences. These non‐uniformities are discussed in terms of recently developed theories of kink‐pair formation and kink‐kink interactions on screw dislocations in bcc metals. The HVEM observations suggest that the mobility of screw dislocations at very low temperatures should be determined by the combined effects of the PEIERLS barriers and the jog dragging.
Slip band growth and dislocation velocities in thin flat crystals of n‐irradiated Cu and Cu‐30% Zn
Authors: Godon H. , Potthoff H.‐H. , Neuhäuser H. 
Published: January 2007

AbstractExtending earlier work (POTTHOFF) the dependence of the arrangement and development of slip bands on the thickness of thin flat single crystals of neutron‐irradiated copper and Cu‐30% Zn orientated for singe glide is studied at room temperature. Distinct differences in the behaviour of thin (20 … 200 μm thickness) and thick (≧ 500 μm thickness) crystals are found. Partly they are connected with the bending stresses in the region of the Lüders band front. The velocities of dislocation groups in the first stages of slip band growth are estimated. The deformation kinetics is discussed in the concepts of viscous glide and nucleation rate of dislocations for both materials.
Strain history effects at low temperature deformation
Authors: Wielke B. , Mikulowski B. 
Published: January 2007

AbstractThe work hardening coefficient of hep metals like Zn or Cd depends on the temperature even at very low temperatures. Additional information of the processes involved can be derived from specially designed annealing experiments. If deformed single crystals of Zn, Zn + 0.2 at.% Ga and Zn + 0.2 at.% Ag are annealed the work hardening increases. The amount of increase depends on deformation temperature and annealing time. The effects observed suggest that the work hardening is determined at least partly by the mobility of points defects.
On the strengthening of Magnesium Single Crystals by Cadmium
Authors: Lukáč P. 
Published: January 2007

AbstractSolid solution hardening in single crystals of magnesium containing cadmium (up to 2.4 at.%) has been investigated in the temperature range 77 K to 295 K. A strong temperature dependence of the critical resolved shear stress, τ0, is observed below 230 K, while above this temperature τ0 is temperature independent. At all temperatures τ0 is found to increase linearly with c2/3, where c is the concentration (in atomic fractions) of cadmium as solute. The concentration dependence of τ0 can be explained by the theory of LABUSCH.
Acoustic emission analysis of the brittle fracture behaviour of intermetallic layers in multifilametary cu‐ga/v superconductors
Authors: Fischer G. , Krumphold R. , Pompe W. 
Published: January 2007

AbstractCombinding mechanical acoustic and SEM investigations, the influence of various heat treatment on the mechanical stability of the intermetallic phase V3Ga of multifilamentary Cu—Ga/V composites is analyzed. The destruction process of the boundary phase consists in cumulative microcracking perpendicular to the fibre orientation. Depending on the mean strength of the boundary layer as well as on the position of the elastic‐plastic transition of the fibre of the boundary layer as well as on the position of the elastic‐plastic transition of th efibre of the matrix, different types of acoustic emission rates are observed. A theoretical model of this behaviour is derived. Under optimum conditions the microcracking of the intermetallic boundary phase can be suppressed nearly completely up to a strain of about 0.8%
Crystal growth of β‐Phthalocyanines from the vapour phase in closed ampoules
Authors: Simonyan M. V. , Grigoryan L. S. , Gasparyan A. G. , Sharoyan E. G. 
Published: January 2007

AbstractAn influence of temperature gradient, inert gas pressure and pulling rate on the growth parameters of β‐phthalocyanine single crystals grown in the closed ampoules is investigated. The morphology and structure — sensitive properties of β‐CuPc crystals grown under different conditions are compared.
Precipitation of Strontium Sulphate
Authors: Sühnel Otakar , Handlířová Marie 
Published: January 2007

AbstractPrecipitation of unseeded supersaturated aqueous solutions of SrSO4 and growth of SrSO4 crystals at the size of approximately 20 μm were studied. Within the examined range of supersaturations, i.e. Sa < 16, the nucleation in aqueous solutions is controlled by the heterogeneous nucleation mechanism. The induction period of precipitation depends on the rates of both the nucleation and growth of the formed nuclei. The growth of SrSO4 crystals in supersaturated solutions at S ⪅ 5.6 is of the 2nd order with respect to the concentration and at temperatures 25 ÷ 45°C the process is controlled by the surface reaction mechanism. The number of crystals in the precipitated slurry is decreasing rapidly as a result of the Ostwald maturing.
Investigations on the homogeneity of single crystals of materials with variable composition grown by chemical transport reactions
Authors: Krabbes G. , Klosowski J. , Oppermann H. , Mai H. 
Published: January 2007

AbstractTo investigate the problem of homogeneity in crystals grown by chemical transport reactions (CTR) solid solutions Fe1‐yCoyS, Fe1‐yNiyS, and Zn1‐yCoyO were choosen as model substances. Relative concentration profiles of Co and Ni, respectively, were measured by electron‐probe microanalysis and light absorption (in Zn1‐yCoyO only). No significant deviations from homogeneity were found for Fe1‐yMeyS, whereas in Zn1‐yCoyO the Co contents increase in the growth direction. A qualitative explanation due to different diffusivities in the solids can be given.
A positron study on the effect of As, Sb, W, and Ti on the annealing of defects in cold‐rolled Ni
Authors: Meyendorf N. , Dlubek G. , Brümmer O. , Baranowski A. , Rozenfeld B. 
Published: January 2007

AbstractThe peak height of the 2γ‐angular correlation curve is measured as a function of the sample temperature during time linear heating of cold‐rolled Ni dilute alloyed with Sb, As, W or Ti (0.03 to 1.4 at.%). The effect of these foreign elements on the annealing of defects is very different. In Ni alloyed with As or Sb the formation of a large number of three‐dimensional vacancy clusters is observed indicated by a strong increase of the peak height. Obviously As and Sb atoms act as nucleation centres for the vacancy clustering. The addition of W to Ni leads to a shift of the vacancy annealing to higher temperatures. In Ni alloyed with Ti relative smooth peak height recovery curves are observed. Positron lifetime measurements show that no vacancy clusters are formed. The effect of the impurities on the vacancy annealing correlates with their binding enthalpy for vacancies in Ni.
Thermoluminescence studies of Al2O3 crystals doped with Cobalt impurity
Authors: Pandaraiah N. , Narasimha Reddy K. , Subba Rao U. V. , Wanklyan B. M. 
Published: January 2007

AbstractThermoluminescence (TL) studies of cobalt‐doped Al2O3 crystals irradiated with X‐rays have shown that the TL glow curve consists of three peaks at 105, 195 and 260°C. Bleaching, annealing and quanching studies have been performed in order to understand the nature of colour centers responsible for the formation of the three peaks. The values of the fundamental parameters like trap depth and frequency factor are estimated from TL data and the results obtained are discussed.
Disclinations and ovals in the Smectic B and E phases
Authors: Demus D. , Schiller P. , Sharma N. K. 
Published: January 2007

AbstractNear to the clearing temperature the formation of the texture of a B phase was investigated. The growth of the B phase is beginning with germs, in shape similar to 2π‐disclinations whic some tenths of a degree below the clearing temperature dissociate to a system of two π‐disclinations. At further lowering the temperature, the latter change to the ovals which contain a set of wedge like material with plane smectic layers. By a competition of surface free energy and elastic free energy the sequence of textures can be explained theoretically.
Liquid crystalline swallow‐tailed compounds I
Authors: Weissflog W. , Wiegeleben A. , Diele S. , Demus D. 
Published: January 2007

AbstractBy reaction of di‐n‐alkyl 4‐hydroxybenzylidene‐malonates with different acid chlorides three homologous series of swallow‐tailed compounds were synthesized. The products were characterized by microscopic and calorimetric investigations and show nematic and smectic behaviour. As X ray studies prove the relatively broad molecules are statistically antiparallel arranged within the smectic monolayers.