bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and properties of Na‐magadiite dependent on temperature
Authors: Brandt Astrid , Schwieger Wilhelm , Bergk Karl‐Heinz , Grabner Paul , Porsch Martin 
Published: January 2007

AbstractThe mechanism of the thermal behaviour of Na‐magadiite at a temperature range from 293–573 K was developed based on X‐ray diffraction, DTA, DTL, Q‐TG, and gravimetric measurements. A structure model (BRANDT et al.) previously proposed was additionally used.It is possible to show that there probably is a connection between the typical modifications of basal spacing and significant shiftings of silicate sheets. Different steps of dehydration, decrystallization and structure variations can be ascribed to the several thermal transitions. The results depend on sample treatment such as the existent or not existent solid‐water vapour interaction and the establishment of equilibrium. It seems that there is a predominance of the first mentioned influence.
The development of a nematic two frequency addressing mixture
Authors: Stettin H. , Kresse H. , Schäfer W. 
Published: January 2007

AbstractAn example is given for the development of a nematic two frequency addressing mixture based on the equations for the threshold voltages, the switching times, and the dielectric relaxation. New substances have been synthesized with relaxation frequencies in the kHz range and big values of the static dielectric anisotropy at room temperature. The isotropy frequency and the relation between the high and low frequency dielectric anisotropy, respectively, are adjustable by adding of substances without a relaxation mechanism in the kHz range and with a big negative static dielectric anisotropy. The produced mixture was dielectrically investigated. Calculated and experimentally found data are in a good agreement.
The coloration effect in KCl: Eu2+ crystals γ‐irradiated at 200 K
Authors: Opyrchal H. , Macalik B. , Nierzewski K. D. 
Published: January 2007

AbstractThe formation of colour centers at 200 K in γ‐irradiated KCl crystals doped with Eu2+ ions in a wide concentration range is studied by optical absorption, EPR, and ITC method. The EPR and ITC measurements reveal the drastic decrease of concentration of isolated europium dipoles induced by irradiation at 200 K. Moreover, no correlation between concentration changes of colour centers and Eu2+ dipoles induced by irradiation and postirradiated annealing has been found. The results obtained are explained by radiation stimulated aggregation of Eu2+ dipoles into small clusters at 200 K.
Preparation of some lanthanide violurate complexes
Authors: Farag I. S. Ahmed , Awadallah R. M. , Gad A. A. M. 
Published: January 2007

AbstractViolurate complexes of Ce3+, Pr3+, Pr4+, Nd3+, Sm3+, Eu3+, Gd3+, Dy3+, Ho3+, Er3+, and Yb3+ were prepared. The prepared complexes are freely soluble in hot water and dilute mineral acids. Thermal analysis (DTA, DTG, and TGA) show that the solid complexes are characterized by endo‐ and exothermic bands, indicating that they are degradated at different temperature stages. The IR spectra of the ligand and its metal complexes reveal that bonding takes place through coordination bonds between the central metal ion and the oxygen atom of the oximino (C = NO) group and the oxygen of the phenolic (ketonic group . All the isomorphous complexes, detected by the X‐ray diffraction patterns, have similar IR spectra.
Liquid phase epitaxial growth of undoped gallium arsenide from bismuth and gallium melts
Authors: Yakusheva N. A. , Zhuravlev K. S. , Chikichev S. I. , Shegaj O. A. 
Published: January 2007

AbstractElectrical properties of undoped GaAs layers grown from Ga and Bi melts under identical conditions are compared as a function of growth temperature and pregrowth baking time. Identification of residual shallow donors and acceptors is performed by means of laser photoelectrical magnetic spectroscopy and low temperature photoluminescence. It is shown that a change of solvent metal results in complete alteration of major background impurities in grown epilayers due, mainly, to changes of distribution coefficients of these impurities. High purity, low compensation n‐GaAs layers can be grown from Bi melt (epilayers with the Hall mobility of electrons μ77K ≈ 150000 cm2/V · sat n = 2.5 · 1014 cm−3 has been grown).
Crystal growth and dislocation structure of gallium antimonide
Authors: Moravec F. , Šestáková V. , Štěpánek B. , Charvát V. 
Published: January 2007

AbstractSingle crystals of GaSb have been grown by the Czochralski method under reducing conditions. Crystals were grown in the 〈100〉, 〈111〉, and 〈112〉 directions. The 〈111〉 growth direction was found to be the most suitable for the successful and reliable crystal growth. Dislocation densities in 〈111〉 oriented crystals were examined by chemical etching. The etch pits density in these crystals didn't exceed the value of 1 × 102 cm−2.
On the preparation and electrical properties of thallium selenide monocrystals
Authors: Hussein S. A. , Nagat A. T. 
Published: January 2007

AbstractThallium Selenide single crystals were prepared by a special design using Bridgmantechnique constructed by the authors. An investigation was made on the influence of temperature on the electrical conductivity and Hall effect in two crystallographic directions. The anisotropic properties were checked, and the anisotropic factor was observed to increase with temperature decrease. The energy gap as well as the ionization energy was calculated. The conductivity throughout the entire temperature range was found to be of p‐type. The Hall mobilities derived from these measurements at room temperature were of the order μH⟂ = 42.66 cm2/vs and μH∥ = 112.2 cm2/vs.
Force constant scaling and interatomic potential in tetrahedral semiconductors
Authors: Neumann H. 
Published: January 2007

AbstractThe force constants of tetrahedral semiconductors derived from lattice vibration data are analysed in terms of a generalized Morse potential and of a potential with power laws of the interatomic distance for the repulsive and attractive term. It is found that the Morse potential is an appropriate model for describing the dependence of the force constants on the bond length in the elemental, AIIIBV, AIIBVI and AIBIIIC semiconductors.
InGaAsP quaternary layers on InP (100) substrate analysed by ion backscattering and channeling
Authors: Flagmeyer R. , Gottschalch V. 
Published: January 2007

AbstractIn1−xGaxAsyP1−y layers LPE grown on InP(001) substrates are analysed by the Rutherford backscattering and channeling techniques. In addition to the layer thicknesses the compositions are determined from the random spectra and compared with the PL and XRD results.The high dechanneling rate of the He+ ions for [100] incidence is attributed to the displaced atoms in the distorted crystal lattice of these otherwise high‐quality epitaxial layers. We find a characteristic value of Δχdist(0.1) = 2.3 ± 0.3% which must be taken into account for estimations of crystalline quality.
Isomorphic substitutions in the CeO2La2O3 system at 850° C
Authors: Minkova N. , Aslanian S. 
Published: January 2007

AbstractIt was proved that there are two isomorphic series of mixed crystals in the CeO2La2O3 systems from 0 to 14 mol% CeO2‐mixed crystals based on the La2O3 structure and from 32 to 100 mol% CeO2‐mixed crystals based on the CeO2 structure. The oxides were obtained by co‐precipitation of oxalates, followed by heating at 850 °C. The changes of the parameters of the lattice with the changes of the composition were investigated. Also the solubility of the mixed crystals in 25% HCl was determined.
Vapour transport of CdCr2S4 and HgCr2Se4: Chemical equilibrium and crystal growth
Authors: Belyaev V. K. , Nikiforov K. G. , Radautsan S. I. , Bazakutsa V. A. 
Published: January 2007

AbstractTheoretical and experimental studies of the CdCr2S4(HgCr2Se4): CrCl3 systems have been performed for the crystal composition control in the chemical transport growth. The balance partial pressures of the components have been calculated in a wide temperature range. It is shown that the CdCr2S4 composition control can take place with the powerful change of the transport agent quantity. Such control for the HgCr2Se4: CrCl3 system is more difficult. The calculated vapour phase composition is in good agreement with the determined one based on the measurements of the sound speed and transport rate.
Comparative infrared lattice vibration study of LiGaO2 and LiInO2 (I) experimental results
Authors: Sobotta H. , Kühn G. , Neumann H. , Riede V. 
Published: January 2007

AbstractInfrared reflectivity spectra of LiGaO2 and LiInO2 samples pressed from powdered material are measured at room temperature in the wavenumber range from 180 to 4000 cm−1. The optical mode frequencies found for LiGaO2 agree with measurements on single crystals. In LiInO2 four vibrational modes are found. Comparing the results for LiGaO2 some conclusions are made with regard to the LiO bond related vibrational modes.
Crystallization of potassium sulphate from glaserite
Authors: Mazzarotta B. 
Published: January 2007

AbstractThe crystallization of K2SO4 from aqueous solutions of glaserite (a double salt of sodium and potassium sulphate) was investigated in an MSMPR cooling apparatus at 35 °C. The precipitation of K2SO4 at an average purity of 93 wt.% was obtained and the crystallization kinetics were derived from the experimental data. The nucleation and growth rates here obtained were, respectively, remarkably higher and slightly lower than those relevant to pure K2SO4: this behaviour may be explained by a faster nucleation and a slower growth of crystals containing also Na2SO4. The effect of small (0.05%) calcium additions to the feed was also tested, which caused an increase of supersaturation and a depression of the growth kinetics, whereas the nucleation one was not appreciably modified.
Growth of manganese tartrate trihydrate in silica gel
Authors: Ramakrishnan V. 
Published: January 2007

AbstractGrowth of manganese tartrate trihydrate crystals in silica gel media with manganese chloride and manganese sulphate as the reactant is attempted. The reason for the occurrence of platelets along with dendrites in the case of manganese sulphate is discussed. IR, X‐ray, atomic absorption and thermogravimetric techniques are employed to characterize the grown crystals and the results are discussed.
An X‐ray diffraction refinement of the crystal structure of natural tetragonal analcime (NaAlSi2O6. H2O)
Authors: Pechar F. 
Published: January 2007

AbstractAn X‐ray diffraction analysis was performed on a single crystal of natural tetragonal analcime: (Na0.99K0.01)/(Al1.05Si2.02) O6/0.99 H2O, space group I 41/acd, a = 13.726(2) Å, c = 13.684(1) Å, V = 2578.1 Å3, Z = 16, Dobs = 2.26. Refinement of 260 independent reflections yields R = 0.028 (Rw = 0.033). The mean Si(Al)O distance is 1.636 Å and tetrahedral angle is 109.35°. The framework of tetragonal analcime is topologically the same as the cubic modification.
Estimation of point defect parameters of solids on the basis of a defect formation model of melting (III). Formation entropy and concentration of schottky defects (vacancies)
Authors: Uvarov N. F. , Bollmann W. , Hairetdinov E. F. 
Published: January 2007

AbstractThe formation entropy of Schottky defects (vacancies) is calculated from the entropy of fusion and the concentration xL = 0.125 of vacancies within the melt at melting point Tm. The formation of vacancies is connected with a decrease of the vibrational frequency of those lattice forming particles (atoms, ions, molecules) being neighbours of the vacancies. Theoretical values of the vacancy concentrations xs agree with those xs obtained with the help of experimentally determined free formation enthalpies of the defects.
Vickers indentation hardness of Hg1−xCdxTe
Authors: Fissel A. , Schenk M. , Engel A. 
Published: January 2007

AbstractThe Vickers indentation hardness of Hg1−xCdxTe has been measured as a function of composition x using monocrystalline samples of Bridgman and THM crystals and polycrystalline starting material at room temperature. The microhardness varied between 220 MPa (x=0) and 440 MPa (x=1), showing a maximum of 850 MPa at x ∼ 0.75, and was different between monocrystalline and polycrystalline samples. The “hardening rate” dH/dx is strongly dependent on the composition range and is discussed in context with solid solution hardening due to elastic interactions of solute atoms with gliding dislocations and ordering effects.
Interatomic force constants in AIIBIVCV2 chalcopyrite compounds
Authors: Neumann H. 
Published: January 2007

AbstractForce constants of the AIICV and BIVCV bonds in the AIIBIVCV2 compounds with chalcopyrite structure are estimated from experimental lattice vibration data using a simplified version of the Keating model. It is shown that the force constants depend exponentially on the bond length. The parameters of this relation are practically the same as those found for the AIVAIV, AIIIBV and AIIBVI bonds in the elemental semiconductors and binary compounds and for the BIIICVI bond in the AIBIIICVI2 semiconductors.
Electrical conductivity and thermal dehydration studies of hydrated barium oxalate and barium cadmium oxalate crystals
Authors: Dharmaprakash S. M. , Rao P. Mohan 
Published: January 2007

AbstractThe measurement of electrical conductivity for the investigation of the number of water molecules present in the hydrated barium oxalate, and barium cadmium oxalate lattice have been carried out in the temperature range 30 to 415 °C. The dehydration temperature and the number of water molecules jettisoned out of the structure at a particular temperature is estimated from the sharp increase in conductivity at these points. The almost abrupt increase of conductivity is attributed to the increase in the number of mobile charge carriers viz., H+ and OH− ions generated from the escaping water molecules. Samples in the form of pellets with and without silver paste applied, showed different behaviour with respect to conductivity of the material upto the completion of dehydration. The study of electrical conductivity in association with the thermal behaviour has been used to understand the mechanism of conduction.
Technological properties of CSK‐1 crystallizer for material research in space
Authors: Barta Č. , Kuhl R. , Trnka J. , Tříska A. , Regel L. L. 
Published: January 2007

AbstractThe crystallizer CSK‐1 is based on a tubular furnace with five heating elements. The crystallizer operates in an automatic mode, i.e., the setting up of the temperature fields, setting of the sample position in the tube and of the rate and direction of their movement are controlled by a microprocessor running according to a program stored on a magnetic tape. The crystallizer is placed on the Soviet Orbital Laboratory “MIR”.Basic technological properties of the crystallizer were studied by means of an standard probe connected with a computer and of the special ARP device, respectively. The topic of the study was especially the creation of various types of axial temperature fields and of various temperature gradients, the rate of heating and spontaneous cooling of the furnace, the temperature stability, and so on.
RHEED investigations of unusual crystalline states in amorphous SiO2 films
Authors: Peneva S. K. , Popova L. I. , Tcukeva E. A. , Atanassova E. D. 
Published: January 2007

AbstractMicrocrystalline regions of silicon dioxide with structures unobserved in the macro‐state are studied by Reflection High Energy Electron Diffraction (RHEED). Their formation can be understood by considering the existence of several possible relatively stable crystalline states of SiO2, with free energies higher than those of the known silicon oxides. SiO2 with structures and lattices identical to the structures and the lattices of the CaF2‐, of the rutile‐type GeO2, and of α‐PbO2 have been identified. Considerations for the state of silicon in some of these structures are also included.
Phase transition studies in 50CB and 80CB
Authors: Venkatacharyulu P. , Gupta A. V. N. , Rao J. V. , Prasad K. S. R. , Prasad N. V. L. N. 
Published: January 2007

AbstractInvestigations on the temperature variation of specific volume and ultrasonic velocity are carried out to study the phase transitions in the liquid crystals 4′‐n‐Pentyloxy‐4‐Cyanobiphenyl (50CB) and 4′‐n‐Octyloxy‐4‐Cyanobiphenyl (80CB). From these studies various parameters like the adiabatic compressibility (βad), molar sound velocity or Rao number (Rn), molar compressibility (B), Van der Waals constant (b) and the intermolecular free lengths (L) are estimated as a function of temperature in the isotropic as well as in the mesophases. Finally the variation of the order parameter with temperature in the nematic phase is studied and the results are discussed.
On cluster kinetics and MBE growth
Authors: Wolf B. , Gantz DP T. , Zehe A. 
Published: January 2007

AbstractBased on the model of a so‐called Near Surface Transition Layer (NSTL) proposed by HERMAN and ANDERSSON we discuss the possible role of clusters during MBE growth. Moreover, intentional use of small clusters instead of single atoms as beam constituents may contribute to improvements in crystal quality even at low substrate temperature and high growth rate.
Wetting of InP by indium‐ and indium‐tin melts
Authors: Mareck DC U. , Gottschalch V. , Butter E. 
Published: January 2007

AbstractOrientation dependent wetting of InP substrates by In‐ and InxSn1−x melts saturated with InP was studied using the sessile drop method. The contact angle was found to depend on the substrate orientation as follows:

It is shown that a tin admixture to the indium melt improves the wetting behaviour. Additional to the dependence on substrate orientation it was found an anisotropic wetting on all investigated faces.
Coefficient of volume expansivity and thermoacoustic parameters in certain alkoxybenzylidene butylanilines‐IA
Authors: Venkatachuryulu P. , Prasad K. S. R. , Prasad N. V. L. N. , Rao J. V. 
Published: January 2007

AbstractA number of thermoacoustic parameters including the Sharma constant So are evaluated in the homologous series of alkoxybenzylidene butylanilines with m = 4 to 7, to understand whether these parameters can be used to understand the anomalous behaviour at the phase transition temperatures and pretransitional effects on either side of the transition. The Sharma constant which was shown to be a constant in a number of non‐mesomorphic systems is also found to be a constant for the mesogens belonging to this series both in their liquid crystalline as well as isotropic state. It is observed that almost all these parameters exhibit anomalous behaviour at the transition and pretransitional effects on either side of the transition. The results are discussed.
The crystallisation of alkaline‐earth metal phosphates from alkaline‐metal halide and alkali metal phosphate melts: Some preliminary solubility‐temperature phase diagram studies
Authors: Packter A. , Doherty W. O. S. 
Published: January 2007

AbstractThe solubility v temperature phase diagrams, for magnesium and calcium meta‐, pyroand orthophosphate solutions in the alkalineearth metal halide melts and in different alkali metal phosphate melts, have been analysed: these are the pseudo‐binary sections of the ternary P2O5MOMX2 and P2O5MONa(K)2O systems at MO/P2O5= 1, 2, and 3, respectively.The temperature ranges and yields for crystallisations of alkalineearth, metal phosphates from these melt solutions are discussed.
The twisting of LiNbO3 single crystals grown by the Czochralski method
Authors: Erdei S. , Gabrieljan V. T. 
Published: January 2007

AbstractAs a result of our experimental work of mainly practical importance we established that for LiNbO3 single crystals the Mg and Fe dopants promote spirality whereas decreasing of the pulling velocity strongly reduces the propensity of the system to produce spiralshaped crystals.
Thermoluminescence and radiation‐induced volume changes in CaF2 (Mn, RE) materials
Authors: Zlateva E. , Levy S. , Gutzow I. 
Published: January 2007

AbstractThe thermoluminescence properties of various CaF2 materials (natural fluorite, CaF2‐glass ceramics and enamels) doped with RE oxides and Mn are investigated in details. Volumetric measurements show that γ‐irradiation leads to a change in the volume density of powder samples of these materials. Depending on the character of the sample, positive (increased volume) or negative dilatation (decreased volume) can be observed during irradiation with doses within the range 1 C/kg–9 C/kg. As time elapses, the radiation‐induced alteration of the sample volume is relaxed and after 2–3 months reaches again the initial volume density of the sample. The unexpected result of radiation‐induced volume changes are discussed in details accounting for supplementary X‐ray, electron microscopy and EPR studies.
Comparing investigation of the smectic C and A phases of the di‐n‐alkyl 4,4′‐azoxycinnamates (II) X‐ray studies
Authors: Diele S. , Schiller P. , Wiegeleben A. , Demus D. 
Published: January 2007

AbstractThe paper continues the investigation of the smectic C and A phases of the title compounds which has been done in Part I by DSC calorimetry. Here the layer spacings in the SC and SA phases are presented which exhibit a remarkable different temperature dependence in the SC phases within the homologous series. A tendency of a change from a second order SC/SA transition to a first order transition has been found. The layer spacings of the SA phase show a chain length dependent difference to the lengths of the molecules which may be explained by an increasing amount of gauche conformations in the higher homologues.
Morphology of TiN whiskers
Authors: Wokulski Z. 
Published: January 2007

AbstractCrystallization of titanium nitride was conducted by the CVD method in a temperature range from 950 to 1450 °C using a TiCl4 + N2 + H2 gas mixture. The influence of type of substrate used on the growth on TiN whiskers was studied. It was ascertained that the growth of TiN whiskers took place at a substrate temperature T ≧ 1200 °C. On the basis of optical microscope and SEM observations and also of X‐ray examination and measurement of angles using an optical reflection goniometer, a detailed description was made of the observed TiN whiskers growth forms. It was found that [111], [110] and [001] whiskers exhibit tip shapes that are characteristic of the given orientation. From the Hartman PBC theory the nature of the faces occurring was determined. It was also shown that the most important is the {111} F face. The stoichiometric composition of the TiN whiskers obtained was estimated and it was ascertained that these whiskers have a composition from Ti0.98 to TiN0.993.
Effect of vibration frequency and sample composition on acoustic properties of YBaCuO high‐Tc superconductors
Authors: Pal‐Val P. P. , Natsik V. D. , Engert J. , Kaufmann H.‐J. , Rudolph K. , Matz W. 
Published: January 2007

AbstractTemperature dependences of absorption and velocity of longitudinal ultrasound in high‐Tc ceramics YBaCuO with different Y and Ba content at frequencies 100 kHz and 7.5 MHz are studied in the temperature range 6 to 300 K. For 100 kHz three peaks at 60, 140, and 230 K are observed in the temperature dependences of decrement. Temperature dependences of sound velocity show a broad hysteresis for thermocycling. The temperature boundaries of hysteresis and peak locations are almost independent of sample composition. Sizes of hysteresis and peak heights are very different in samples of various composition. For 7.5 MHz, a peak was found at 210 K in the temperature dependences of ultrasound absorption increment. It is shown that the acoustic anomalies are due to a structural phase transition of martensitic type. Thermoactivation parameters of the main microscopic mechanism responsible for the phase transition are estimated.