Structural Characterization of Y2Pd14B5

Y₂Pd₁₄B₅ is the major phase in as‐cast and annealed multiphase alloys with nominal compositions near YPd₅B₃C_0.3. Its crystal structure determined the first time here by single crystal X‐ray diffraction is body‐centered tetragonal (space group I4₁/amd). Transmission electron microscopy (TEM) reveals that in as‐cast specimens the tetragonal phase has a modulated structure and is oriented intergrown with a face‐centered cubic phase of similar composition, namely YPd₇B₂. According to Rietveld analyses of the multiphase system the structure of this phase can be well‐described by space group Fm m. Annealing the sample for 150 hrs at 973 K results in a coarsening and enrichment of the tetragonal phase as well as a disappearance of the modulations allowing a detailed structure analysis by single crystal diffractometry.     

X-ray Studies on the Liquid Crystalline Phases of the 4-[4-n-Heptyloxy-Benzylidene-Amino]4'-cyanobiphenyl

By means of X-ray diffraction studies of oriented and non-oriented samples the lattice parameters of the orthorhombic cell of the S_E phase as well as of the hexagonal cell of the S_B phase were determined. By packing considerations a bimolecular building unit with oppositely arranged cyano-groups was assumed in the case of the S_E phase. The S_B phase is characterized by an ABAB sequence of the smectic layers in which the molecules are hexagonal arranged. The increasing mobility of the molecules at increasing temperature offers the possibility for a part of the molecules to slide in a more stable dimerized form. In the N_R and S_A phase the existence of monomers as well as of dimers is assumed. In this way a conception of the phase transitions S_E → S_B → N_R → S_A is given on the base of a decrease by steps of the dipole-dipole repulsion.     

Interplay between phase formation mechanisms and magnetism in the Sr2FeMoO6–δ metal‐oxide compound

Double perovskites with the structural formula A₂BB′O_6±δ, especially the strontium ferromolybdate Sr₂FeMoO_6–δ, have attracted a lot of attention due to their unique magnetic and electrical properties and a possible application in spintronic devices. However, a strict correlation between the functional characteristics of Sr₂FeMoO_6–δ and its synthesis technology has been lacking up to date. Thus, we have studied in the present work the crystallization kinetics of Sr₂FeMoO_6–δ using reagents with different pre‐history as well as the structural and magnetic properties of the obtained compounds. Differences in the crystallization kinetics as well as higher magnetic inhomogeneity of Sr₂FeMoO_6–δ synthesised from a mixture of MoO₃, Fe₂O₃, SrCO₃ in comparison with the compound synthesised from the SrFeO_2.5 and SrMoO_4–y precursors have been found and interpreted. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lifetime of dominant radicals for the deposition of a-Si:H from SiH4 and Si2H6 glow discharges

Deposition kinetics of a-Si:H from Si₂H₆ as well as SiH₄ glow discharge has been investigated using a triode reactor with a variable electrode-substrate distance. The results of deposition rate and OES (optical emission spectroscopy) indicate that dominant radicals as a film precursor are different between SiH₄ and Si₂H₆ plasma and the radical in Si₂H₆ has a much shorter lifetime than that in SiH₄.     

Iodine Intercalation of Bi2Sr2Ca(n−1)CunOy(N=2,3) Superconductors by Using Reactants I2 or FeI2

Abstract

The change of superconductivity induced by intercalation is very interesting We have investigated on intercalation into Bi2212 single crystal and Bi2223 polycrystalline superconductors using FeI₂ or I₂ as reactant. The iodine intercalation by using FeI₂ as a reactant into Bi2223 phase is reported for first time as long as we know. In iodine intercalation into Bi2212 by using FeI₂ as reactant, the critical tem T_Conset in out-of-plane measurement has suddenly decreased on X=0.95. Similar changes of T_Conset with higher X have been observed independent of directions and reactants. T_Conset of I_xBi₂Sr₂CaCu₂O_y intercalated by FeI₂ is a little lower than one of I_xBi₂Sr₂CaCu₂O_y intercalated by I₂. This is likely due to the change of hall concentration induced by reduction of host In iodine intercalation into Bi2223, the smaller change of T_Conset with increasing amount of intercalant is likely due to the number of CuO₂ planes between ntercalant layers.     

Undoped amorphous SiNx: H alloy semiconductors: Dependence of electronic properties on composition

The electrical and optical properties of a-SiN_x:H thin films prepared by rf growth-discharge in SiH₄N₂H₂ without B or P doping have been measured for 0 < x ? 0.6. It is observed that the activation energy for extended-state electron conduction as well as the optical gap are unaffected by N content for x ? 0.4. The electron mobility in extended states is improved by as much as a factor of 10 by the N incorporation. There is a rapid conversion from the tetrahedral network to a Si₃N₄ network as x increases above ≈ 0.4.     

Scattering losses in binary borate glasses

The purpose of this paper is to examine the potential of three binary borate glasses; namely PbOB₂O₃, K₂OB₂O₃ and Li₂OB₂O₃ as candidates for fabrication of low optical loss and low cost fiber-glass wave-guides.The importance of ultrasonic measurements as the first step in a systematic search for a glass with low optical loss, is discussed. Results of ultrasonic measurements of PbOB₂O₃ system are then presented. Using these results and the published results for the K₂OB₂O₃ and Li₂OB₂O₃ systems, estimates of the magnitude of density fluctuations as a function of composition have been made for each system. Comparison with the previously published results on the K₂OSiO₂ system suggests that out of the three systems chosen, only 50 mole % Li₂O50 mole % B₂O₃ glass is a likely candidate for the production of low optical loss glass fibers.     

Thermal properties of barium titanium borate glasses measured by thermal lens technique

In this paper, thermal lens spectrometry was used to determine the thermal properties of barium titanium borate glasses as a function of the amount of TiO₂ in the ratios 8/9 and 1/1 of BaO–B₂O₃. The thermal lens technique was shown to be sensitive to the variation of TiO₂ and the ratio of BaO/B₂O₃, through thermal diffusivity and conductivity, with different behavior for the ratios 1/1 and 8/9. An increase in thermal diffusivity and conductivity as a function of TiO₂ was observed, and this behavior was ascribed to the fact that titanium acts as a glassy-former, being more active in the ratio 8/9.     

Changes of the Dispersive and Phase Composition of Cerox Type Polishing Material as a Result of Exploitation and Mechanoactivation

The changes of the dispersive and phase composition of a Cerox type polishing material as a result of its exploitation and mechanochemical treatment are studied. A slightly expressed destruction of the solid solution CeO₂-Ln₂O₃ during the exploitation and mechanoactivation in water suspension (in centrifugal ball mill) is found out. The mechanoactivation models very well the changes of the dispersive composition of the polishing powder as a result of its use. A similarity in the behaviour of the wasted and the mechanoactivated materials is observed in the case of a treatment with HNO₃+H₂O₂ mixture as well.     

Pressure effects on electrical conduction in glasses

Electrical conduction in various inorganic glasses was studied as a function of hydrostatic pressure up to 2000 atm and phenomenologically classified into electronic, ionic and mixed types. In electronically conducting glasses such as AsSe chalcogenide glasses and Fe₂O₃P₂O₅ glass, the conduction is enhanced by application of pressure. On the other hand in ionically conducting glass such as Na₂OB₂O₃ glass, the conduction is suppressed through the concept of an activation volume. The compatibility of electronic and ionic conduction processes in glasses such as Ag-doped AsSe glasses and Bi₂O₃B₂O₃ glass, which have more complex conduction processes, was discussed from these aspects.     

Synthesis of vanadium dioxide thin films on conducting oxides and metal–insulator transition characteristics

We report on growth and physical properties of vanadium dioxide (VO₂) films on model conducting oxide underlayers (Nb-doped SrTiO₃ and RuO₂ buffered TiO₂ single crystals). The VO₂ films, synthesized by rf sputtering, are highly textured as seen from X-ray diffraction. The VO₂ film grown on Nb doped SrTiO₃ shows over two orders of magnitude metal–insulator transition, while VO₂ film on RuO₂ buffered TiO₂ shows a smaller resistance change but with an interesting two step transition. X-ray photoelectron spectroscopy has been performed as a function of depth on both sets of structures to provide mechanistic understanding of the transition characteristics. We then investigate voltage-driven transition in the VO₂ films grown on Nb-doped SrTiO₃ substrate as a function of temperature. The present study contributes to efforts towards correlated oxide electronics utilizing phase transitions.     

The precipitation of sparingly-soluble alkaline-earth metal phosphates in gelatine gels by diffusion of anion (i). the precipitation of calcium hydrogen phosphate dihydrate and basic calcium phosphates

The precipitation of different calcium phosphates in gelatine gels was studied by diffusion of disodium hydrogen phosphate solutions into ten percent gels containing calcium cation at liquid gel pHs from 6 to 11. At pHs 6.0 to 7.5, calcium hydrogen phosphate dihydrate (CaHPO₄ · 2 H₂O) was deposited as a continuous precipitate and then as rings of precipitate (the Liesegang phenomenon): their spacing coefficients varied with the reciprocal initial anion concentrations according to the Packter-Matalon relation. At liquid gel pHs 8.0, 8.5, tretacalcium phosphate (Ca₄H(PO₄)₃) was deposited as a continuous precipitate. At liquid gel pHs from 8.5 to 11, hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, Ca/P ratios = 1.50 to 1.67) was deposited as a continuous precipitate. The mechanisms of precipitation of the different calcium phosphates (in gelatine gels) is briefly discussed.     

Preparation of lithium ion conducting glasses and glass–ceramics for all-solid-state batteries

Highly lithium ion conducting glasses and glass–ceramics were prepared by a mechanical milling technique in the Li₂S-based sulfide and oxysulfide systems. The Li₂S–P₂S₅ glass–ceramics showed ionic conductivity as high as 3.2 × 10^?3 S cm^?1 at room temperature. All-solid-state batteries using these sulfide-based materials as a solid electrolyte showed excellent charge–discharge performance with high capacity and high cycleability. The cells with the combination of the SnS–P₂S₅ glassy electrode and the Li₂S–P₂S₅ glass–ceramic electrolyte worked as a secondary battery, which was a first step of glassy monolithic cells with a common glass network.     

Czochralski Growth of Potassium Lithium Niobate Single Crystals with Low Li Content and Their Characterization

Single crystalline and crack free potassium lithium niobate (KLN) single crystals with low Li content were grown by the Czochralski method. The crystal composition can be written as K_2.60Li_1.17Nb_5.44O₁₅ (=K_2.95Li_1.33Nb_6.17O₁₇) which contain relatively fewer Li ions than ferroelectric K₃Li₂Nb₅O₁₅ crystals. All experimental results show that the deficiency of the Li ions in the KLN crystals strongly influences their physical properties. Especially, the as‐grown crystals do not indicate any signature for a ferroelectric phase transition in contrast to the ferroelectric K₃Li₂Nb₅O₁₅ crystals. However, due to ionic conduction, the temperature dependence of the dielectric constant of such KLN‐2 crystals show a broad anomaly near 300°C. In addition, the existence of proton defects can be revealed by infrared absorption spectroscopy near 3500 cm^‐1 in as‐grown crystals.     

Reconstruction of the -GaO (1 0 0) cleavage surface to hexagonal GaN after NH nitridation

The potential use of β-Ga₂O₃ wafers as transparent conductive substrates for compounds with hexagonal structure, in particular the GaN-system, is shown. Nitridation of the main cleavage plane under high temperature and NH₃ gas results in the substitution of O by N on the surface, and a simultaneous surface reconstruction. The 2-fold symmetry of the initial (1 0 0) plane changes to a 6-fold symmetry, keeping the [0 1 0] azimuth as a symmetry direction. The RHEED pattern suggests the formation of GaN on the β-Ga₂O₃ surface, with the b-axis of β-Ga₂O₃ parallel to the direction of GaN, so that β-Ga₂O₃ can be used as a substrate with no lattice mismatch to GaN.     

Influence of superheat before quench on the structure and stability of NiP metallic glasses studied by neutron scattering techniques

The temperature dependent structure of Ni₈₁P₁₉ metallic glasses, rapidly quenched from melts which have undergone different heat treatments, has been investigated by small angle neutron scattering and neutron diffraction. All samples contain in the as-quenched state particles or clusters of a very wide range of sizes. These are amorphous regions of different compositions in a large composition range and/or crystallites of another Ni composition than the matrix, such as Ni₃P, Ni₅P₂ or Ni₁₂P₅, or even “voids”. The results can be interpreted within the concept of a heterogeneous structure existing in eutectic melts in a certain temperature range. Comparison is made with results from the literature on samples from the same ribbons investigated by calorimetry as well as by fractography and Weibull analysis of mechanical properties.     

Characterization of new sulfur and selenium-based glasses containing lead iodide

The aim of this work is to investigate and qualify vitreous regions in new chalcogenide systems containing highly polarizable elements like S, Se, As, Sb, Bi, Pb and I. The sulfur based system, As₂S₃-Sb₂S₃-Bi₂S₃-PbI₂, as well as the selenium containing glasses As₂Se₃-Sb₂Se₃-PbI₂ have been studied. Large vitreous regions have been defined in the both systems: sulfur and selenium. Indeed, several glass compositions can accept in the vitreous network a molar concentration near 50% of PbI₂. Physical properties such as glass transition temperature, crystallization temperature, optical transmission, band-gap wavelength have been measured versus glassy compositions.     

A novel growth method for ZnAl2O4 single crystals

ZnAl₂O₄ is a well‐known wide band gap compound semiconductor (E_g=3.8eV), ceramic, opto‐mechanical, anti‐thermal coating in aero‐space vehicles and UV optoelectronic devices. A novel method for the growth of single crystals of a ternary oxide material was developed as a fruit of a long term work. Material to be grown as metal incorporated single crystal was taken as precursor and put into a bath containing acid as reaction speed up reagent (catalyst) as well as solvent with a metal foil as cation scavenger. Using this method, ZnAl₂O₄ crystals having hexagonal facets are prepared from a single optimized bath. Structural and compositional properties of crystals were studied using Philips, Xpert ‐ MPD: X‐ray diffractometer and Philips, ESEM‐TMP + EDAX. Thus technique was found to be a new low cost and advantageous method for growth of single crystals of ternary oxide a material. We hope that these data be helpful either as a scientific or technical basis in material processing. Dedicated to Prof. P. Ramasamy © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Studies on the formability of Al-based metallic glasses/nanocomposites based on isochronal DSC analysis

The Al₈₆Si_0.5Ni_4.06Co_2.94Y₆Sc_0.5 metallic glass of highly improved glass-forming ability (GFA) has been investigated by isochronal differential scanning calorimetry measurements, as well as the Al₈₅Ni₅Co₂Y₈ for comparison. The experimental results indicate that the Al₈₆Si_0.5Ni_4.06Co_2.94Y₆Sc_0.5 exhibits enlarged temperature interval between the first and second crystallization onsets (termed as primary fcc-Al/glass region), as well as enlarged second activation energy (E_p2) against the nucleation and the growth of intermetallic compounds besides fcc-Al. The variation of the Avrami exponent demonstrates that the primary crystallization process is a rapid two- and three-dimensional diffusion-controlled nucleation and growth mechanism initially, and the whole process is strongly controlled by the growth of fcc-Al crystals. According to the analysis on the basis of atomic mobility of alloy components, it demonstrates that the enlarged primary fcc-Al/glass region obtained through proper coexistence of dissimilar and similar elements would be in favor of preparing Al-based metallic glasses or nanocomposites in greater size.     

Heterogeneous structure of the quaternary metallic glass Fe40Ni40P14B6: An EXAFS investigation

The problems encountered in the analysis of EXAFS data from Fe₄₀Ni₄₀P₁₄B₆ are solved by assuming a micro-heterogeneous structure from chemically and structurally different micro-phases. A special Bayesian-type least-squares algorithm with general constraints was developed to reduce the effective number of free parameters, which fits simultaneously the EXAFS spectra at the NiK and the FeK edges and maximum prior knowledge as available. As a result of the analysis, the decomposition into micro-phase regions with Fe₃B-type short-range order (52%) as well as random dense packed FeNiPB solid solution regions (48%) is proposed.