Structural,electronic properties and chemical bonding in protonated lithium metallates Li<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MO<Subscript>3</Subscript> (M = Ti,Zr, Sn)

Within density functional theory by an ab initio molecular dynamics method (SIESTA code) the features of structural, electronic properties and chemical bonding in lithium metallates Li₂MO₃ (M = Ti, Zr, Sn) are studied, as well as of their protonated forms Li_2−x H _x MO₃ at all possible H⁺ → Li⁺ substitutions. With the use of the calculated crystal orbital overlap populations and the formation energies of Li_2−x H _x MO₃ the most preferred H⁺ → Li⁺ substitutions in Li₂MO₃ metallates are discussed.     

Effect of Metallic Oxides Containing Composite Electrodes on Crystallization and Ferroelectric Properties of Pb(Zr0.52,Ti0.48)O3 Thin Films Deposited by the Sol-Gel Method

In order to suppress polarization fatigue and decrease the leakage current of the PZT capacitor, composite electrodes consisting of MO₂ (RuO_x or IrO_x) as an effective diffusion barrier and considerably large amounts of Pt were deposited by magnetron co-sputtering to yield heterostructured PZT capacitors, Pt/(Pt+MO₂)//PZT(52/48)//(Pt+MO₂)/(Pt+M)/M/Pt/Ti(Ta)/SiO₂/Si(1 0 0), and the crystallinity and the orientation, the morphology of the surface and the cross section, and the composition depth profile of the PZT capacitor were examined by XRD analysis, SEM and AES, respectively, and the ferroelectric properties were measured. The results indicated that by adjusting the distribution and composition of the RuO₂ phase, the polarization loss of the PZT capacitor can be suppressed to as small as 5% after polarization reversals of 10⁹ while maintaining the effective polarization dP_r = P_r* – P_r ^{^} at 15 C/cm². The suppression of the polarization fatigue was found more effective with (Pt+IrO₂) electroding than (Pt+RuO₂) electroding. The leakage current of the PZT capacitor electroded with (Pt+MO₂) was a little larger than that of the PZT capacitor with Pt electrode. The possible reason was suggested.     

Thickness, Morphology and Structure of Sol-Gel Hybrid Films: II—The Role of the Solvent

The influence of the solvent on the thickness, morphology and structure of silica-polytetrahydrofuran hybrid films, prepared by spin coating, has been analysed. The inorganic precursor, tetraethylorthosilicate, was hydrolysed under acid catalysis, the hydrolysis molar ratio being 4. Polymers of average molecular weight (M _n) 650 and 2900 were incorporated in the initial colloidal solutions, in a low concentration (organic/inorganic molar ratio 0.01). Two solvents were compared: ethanol, protic, and tetrahydrofuran, aprotic and a little less polar. The thickness and surface texture parameters of the films were determined by profilometry, their morphology characterized by SEM and their structure studied by FTIR. It is shown that the solvent has no effect on the molecular structure of the films, but strongly influences the surface texture and the morphology of both pure silica and hybrid films. The solutions prepared in tetrahydrofuran present shorter gelation times (t _G) and allow the deposition of good quality films almost up to the gelation point (to a reduced time, t/t _G, of 0.9). The films are thinner than those prepared from corresponding ethanolic solutions at the same reduced ageing times. For pure silica films, tetrahydrofuran is the best choice, since it reduces the fractured region on the edge of the substrate. For hybrid films, this effect is achieved by the polymer and tetrahydrofuran is responsible for a higher arithmetical mean roughness. Therefore, ethanol becomes the preferable solvent.     

Coefficients of Linear Thermal Expansion of Solid Electrolytes with Co-cation Conduction Based on γ-K4P2O7, γ-KFeO2, and γ-LiAlO2 Structures

Linear thermal expansion coefficients (K) for co-cation solid electrolytes of three types are measured. The electrolytes include solid solutions (K_{1 – x} Rb _x )_3.8Me_0.1P₂O₇ (Me = Ca, Ba) with the structure of -K₄P₂O₇ (I); fcc-solid solutions (A_{1 – x} A" _x )MO₂–EO₂ (A, A" = K, Rb, Cs; M = Al, Ga, Fe; E = Si, Ge, Ti) of -KFeO₂ type (II); and tetragonal solid solutions 0.8(Li_{1 – x} Na _x AlO₂) · 0.2TiO₂ with the LiAlO₂ structure (III). Dependences of K on the ratio of alkali cation amounts in I and II have a maximum, i.e. the polyalkali effect (PAE) of K is observed, while in III this dependence is practically linear (PAE of K is absent). The correlation is found between PAE of K and the electroconductivity of the electrolytes.     

Formation Behavior and Optical Properties of Transparent Inorganic-Organic Hybrids Prepared from Metal Alkoxides and Polydimethylsiloxane

The formation behavior of the transparent inorganic-organic hybrids prepared from silanol-terminated polydimethylsiloxane (PDMS) and metal alkoxides of Al (III), Ti (IV), Zr (IV), Nb (V) and Ta (V) chemically modified with ethyl acetoacetate (EAcAc) has been investigated. EAcAc bonded to metal alkoxides remained in hydrolyzed solutions and gels to prevent the rapid growth of large inorganic particles. It is speculated that extremely small inorganic clusters are dispersed uniformly in PDMS, resulting in the transparent hybrids. The upper limit of M(OR)_n/PDMS ratio to obtain transparent hybrids was influenced by the inorganic source. As the number of remaining alkoxy groups in the modified alkoxide M(OR)_{n – x}(EAcAc)_x increased, the fabrication of transparent hybrids became difficult. The refractive index depended on the inorganic sources reflecting the difference in polarizability of the incorporated metallic ion and the molar volume of the hybrid. The refractive index increased in the order Al (III) < Zr (IV) Ti (IV) < Ta(V) Nb (V).     

Electrocatalytic Oxidation of Ethylene Glycol at Pt/Nanosized MOx/GC Composite Electrodes: SnO2 in Comparison to CeO2 and WO3

Stable metal oxides insoluble in acidic medium have been prepared and characterized. The influence of the type of metal oxide (MO_x) on the activity of Pt towards ethylene glycol oxidation in acidic medium has been examined. All modified Pt/MO_x/glassy carbon (GC) electrodes exhibited a better activity compared to Pt/GC. While Pt/SnO₂/GC electrode exhibited the highest activity, Pt/CeO₂/GC revealed the best tolerance against poisoning process.     

Synthesis of Calcium Phosphates by PO(OH)x(OBut)3−x and CaO2C2H4

In this work, an alkoxide solution route to synthesize Ca phosphates was developed. For the precursors, a CaO₂C₂H₄ solution was prepared by dissolving Ca metal powder into ethylene glycol, and a PO(OH)_x(OBut)_3–x solution was prepared by dissolving P₂O₅ inton -butanol under reflux conditions. In order to obtain a mixed solution of the two precursors, acetic acid was used as an additive. The experimental results show that (1) -2CaO · P₂O₅, -3CaO · P₂O₅, and hydroxyapatite can be easily synthesized by converting the corresponding mixed solutions to powder products in a hot plate, and calcining the as prepared products at 1100°C; (2) acetic acid behaves as a good agent for controlling the reactions between the two precursors by modifying the CaO₂C₂H₄ species in solution and decreasing the reactivity of the PO(OH)_x(OBut)_3–x species.     

Effect of Niobium Modifications to PZT (53/47) Thin Films Made by a Sol-Gel Route

Niobium-modified lead zirconate titanate thin films (PNZT) with nominal compositions, Pb_(1–0.5x) (Zr_0.53 Ti_0.47)_1–x Nb _x O₃:x = 0.02–0.07, have been prepared using a diol based sol-gel route. Single-layer (0.5 m) films were fabricated on platinised silicon substrates by spin-coating. The effect of niobium additions with regard to phase development, microstructure, and ferroelectric and dielectric properties were investigated for different annealing temperatures. For comparison, unmodified PZT films were also prepared. Niobium substitution increased the crystallisation temperatures for perovskite PNZT phase formation. The values of remanent polarisation P _r and dielectric constant _r were found to decrease with the introduction of Nb. For example, in films heated at 700°C for 15 min, the P _r value of an unmodified PZT film was 31 C cm^–2, compared to 17 C cm^–2 for an x = 0.05 PNZT film, whilst respective relative permittivity values fell from 1190 to 600. The highest Nb concentration film, x = 0.07, did not display any switchable polarisation characteristics, which is consistent with high levels of intermediate pyrochlore phase.     

Epitaxial Growth of Sr x Ba1 − x Nb2O6 Thin Films Prepared from Sol-Gel Process

In this study, we prepared Sr _x Ba_{1 – x} Nb₂O₆ (x = 0.3, 0.5 and 0.7) thin film on 0.75 wt% La doped SrTiO₃ (100) and (110) single crystal substrates. A homogeneous coating solution was prepared with Sr and Ba acetates and Nb(OEt)₅ as raw materials, and acetic acid and diethlene glycol monomethyl ether as solvents. The substrates were coated with the solution by spin coating method. As-coated thin films were heated from 973 to 1273 K in air. The grains of the thin film on La doped SrTiO₃ (100) were pillar shaped and arranged in right angle to each other. On the other hand, the grains of these thin films on La doped SrTiO₃ were pillar shape and arranged in one direction. The crystallographic relationship of the thin film between Sr _x Ba_{1 – x} Nb₂O₆ and substrate that the 130 and 310 direction of the thin film on the substrate were oriented with c-axis in parallel to the substrate surface. On the other hand, (hk0) phase diffractions of Sr _x Ba_{1 – x} Nb₂O₆ thin film on the substrate (110) were investigated in the XRD theta-2theta measurement. It is expected that the Sr _x Ba_{1 – x} Nb₂O₆ (x = 0.3, 0.5 and 0.7) were highly oriented or epitaxial growing on La doped SrTiO₃ (110) single crystal substrate.     

Microporous SiO2 and SiO2/MOx (M=Ti,Zr, Al) for ceramic membrane applications: A microstructural study of the sol-stage and the consolidated state

Microporous SiO₂ and SiO₂/MO₂ (M=Ti, Zr, Al; 10 mol% MO_x) materials for gas separation membrane applications have been prepared from polymeric sols. Characterization of these sols with SAXS showed that the mean fractal dimension of the SiO₂ sols is 1.3–1.4 with a radius of gyration of approximately 2.5 nm. The dried and calcined films are microporous and the pore size distribution was bimodal with maxima at diameters of 0.5 nm and 0.75 nm. For the SiO₂/TiO₂, SiO₂/ZrO₂ and SiO₂/Al₂O₃ systems, much milder reaction conditions proved to be necessary to obtain sols with comparable fractal dimensions due to the high reactivity of the Ti/Zr/Al-alkoxides. Microporous supported membranes with molecular sieve-like gas transport properties can be prepared from a relatively wide range of sol structures: from polymers too small to characterize with SAXS to structures with fractal dimensions: 1<d _f<2.04.     

Thermoelectric properties of Cu-doped n-type (Bi2Te3)0.9–(Bi2−xCuxSe3)0.1(x=0–0.2) alloys

n-Type (Bi₂Te₃)_0.9–(Bi_2−xCu_xSe₃)_0.1 (x=0–0.2) alloys with Cu substitution for Bi were prepared by spark plasma-sintering technique and their structural and thermoelectric properties were evaluated. Rietveld analysis reveals that approximate 9.0% of Bi atomic sites are occupied by Cu atoms and less than 4.0 wt% second phase Cu_2.86Te₂ precipitated in the Cu-doped parent alloys. Measurements show that an introduction of a small amount of Cu (x0.1) can reduce the lattice thermal conductivity (κ_L), and improve the electrical conductivity and Seebeck coefficient. An optimal dimensionless figure of merit (ZT) value of 0.98 is obtained for x=0.1 at 417 K, which is obviously higher than those of Cu-free Bi₂Se_0.3Te_2.7 (ZT=0.66) and Ag-doped alloys (ZT=0.86) prepared by the same technologies.     

Structural Features of Grafted Phosphates in Mesopores of Si-MCM-41 and Ti,Si-MCM-41 Molecular Sieves

We have used ³¹P NMR (MAS) and IR spectroscopy and also chemical analysis to show that when Si- and Ti,Si-MCM-41 mesoporous molecular sieves are treated with phosphorus oxychloride, surface-anchored silicophosphate and titanophosphate compounds are formed of the type (Si—O) _x —{PO(OH)_3–x } and (Ti—O) _x —{PO(OH)_3–x } (x = 1, 2), and also compounds with the structure of titanium hydrophosphate and pyrophosphate.     

The influence of hydrogen-containing molybdenum and tungsten bronzes on the catalytic activity of palladium composite catalysts for the oxidation of H<Subscript>2</Subscript>, CO,and CH<Subscript>4</Subscript>

The influence of hydrogen-containing molybdenum and tungsten bronzes on the catalytic activity of palladium composite catalysts for the oxidation of H₂, CO, and CH₄ was studied. It was found that the composite catalysts containing H _x MO₃ phases (M = W or Mo), which were formed by the reduction of MoO₃ and WO₃ oxides with hydrogen in the presence of deposited Pd, showed higher catalytic activity in the oxidation of small molecules (H₂, CO, and CH₄) with excess oxygen than the traditional Pd/Al₂O₃ deposited catalyst with the same content of the deposited metal. It was shown that the thermal stability of the H _x MO₃ phases was the limiting factor influencing the activity of these composite catalysts.     

Positron annihilation studies in YBa2Cu3O x (6<x≤7)

Positron lifetime and Doppler broadening of the annihilation line measurements, as a function of temperature between 14 and 300 K, have been performed on four YBa₂Cu₃O _x (6<x7) samples with different oxygen deficiency. It was found that the positron lifetime and theS parameter values increase as the oxygen deficiency increases in the YBa₂Cu₃O _x (6<x7) samples. It was also observed that the positron annihilation parameers show different temperature dependence in the YBa₂Cu₃O _x (6<x7) samples associated with their different oxygen deficiency.     

Erbium-Activated Silica-Titania Planar Waveguides

(100 – x)SiO₂-(x)TiO₂-ErO_3/2 planar waveguides, with 7 x 20 have been prepared by sol-gel route using the dip-coating technique. The thickness of the films was optimized to support a single propagating mode at 1550 nm, with a confinement coefficient higher than 0.75. The process of densification of the gel and the devitrification with the growth of TiO₂ nanocrystals were studied by Raman scattering. Devitrification is important only for x 15, but it was not possible to obtain full densification of the samples, even at the lowest TiO₂ content, without the appearance of nanocrystals.Emission in the C telecom band was observed; the spectral width of the ⁴I_13/2 ⁴I_15/2 transition of Er³⁺ slightly increases with the titania content. For x 12 most of Er³⁺ ions (about 65%) decay exponentially with a lifetime of about 8 ms.     

Magnetism in mixedHeusler alloys (Ni1−x Cu x )2MnSn

QuarternaryHeusler alloys of composition (Ni_1–x Cu _x )₂MnSn were prepared withx=0–1. They were all single phased with L2₁ structure. Alloys were investigated by magnetic measurements. For Mn, the only atom carrying a moment in this kind ofHeusler alloys, the usual value (4 µ_B) was found and a corresponding _eff in the paramagnetic region. A shallow minimum of theCurie temperatures can be explained on the basis of d_i-d_l interaction.

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Magnetismus von quarternärenHeusler-Legierungen (Ni_1–x Cu _x )₂MnSn

Zusammenfassung QuarternäreHeusler-Legierungen der Zusammensetzung (Ni_1–x Cu _x )₂MnSn wurden über den Konzentrationsbereichx=0–1 hergestellt. Alle waren einphasig und zeigten L 2₁-Struktur. Magnetische Messungen wurden sowohl im ferromagnetischen als auch im paramagnetischen Bereich durchgeführt. Sie ergaben für Mn, das einzige Atom das in dieser Art vonHeusler-Legierungen ein Moment zeigt, den üblichen Wert von ca. 4 µ_B und ein ihm entsprechendes _eff im paramagnetischen Bereich. Ein flaches Minimum derCurietemperatur kann mit Hilfe von d_i-d_l-Wechselwirkung erklärt werden.

     

Three-dimensional configurations of organic/inorganic hybrid nanostructural blocks (I). A quantum mechanical investigation for ladder-like structure of vinylsilsesquioxane

Silsesquioxanes (SSO) or polyhedral oligomericsilsesquioxanes (POSS) are generally prepared frommolecular precursors using the hydrolytic condensa-tion of trialkoxysilane, RSi(OR')3. They are organic/inorganic hybrid nanostructural blocks with theircomplete general formula Tn(T = RSiO1.5, n = 1,2, …), and the incomplete generic formula is Tn-(OH)x(OR')y[x, y = 0, 1, 2, …, T= RSiO1.5 ?(x+y)/2n][1,2].Each VSSO, possessing a certain structural formulaand molecular weight, may h…     

Fluoride-conducting Electrolytes Based on Doped Oxyfluorides Pb1 – xAlxF2 + x–2yOy

Employing materials with fast transport of fluoride ions in chemical power sources and gas sensors requires synthesizing new materials with a wide range of electric properties. High conductivity of -PbF₂can be provided by introducing trivalent ions, which create excess concentration of fluoride ions in -PbF₂. Experimental data on the ionic conductivity of Pb_{1 – x} M _x F_{2 + x} , where M is In, Sb, or Bi, are presented in [1–3]. For the first time brief information about high ionic conductivity of doped Pb_{1 – x} Al _x F_{2 + x– 2y} O _y was reported in [4]. Here, we study in greater detail ionic conduction of neat Pb_{1 – x} Al _x F_{2 + x– 2y} O _y and that doped with fluorides of transition metals Zn, Cu, Ni, Co, Mn, Cr, V, or Ti in the temperature range 272–473 K.     

Polyphosphazenes combining dioxybiphenyl and butyl-amino substituents, a series with unusually high TGA residues and glass transition temperatures with negative deviation from additivity

The new copolymeric series {[NP(O₂C₁₂H₈)]_1−x[NP(NHBuⁿ)₂]_x}_n (O₂C₁₂H₈2,2′-dioxy-1,1′-biphenyl) with x = 0.1(1a), 0.31(1b), 0.43(1c), 0.63(1d) were prepared by the alkali carbonate-assisted sequential macromolecular substitution from [NPCl₂]_n. The thermal gravimetric analysis (TGA) revealed that although the stability decreased with x, the final residues (ca. 50% at 800 °C under N₂; 30% at 900 °C under air; and 15% at 1100 °C under oxygen) were unusually high. The variation of the glass transition temperatures with x showed negative deviation from the additive values (Fox equation), probably due to the losing of hydrogen bonding contribution as x is decreased.     

Use of ethyl oxamate for syntheses of oxamato(-1) and novel μ-oxamato(-2) complexes

Summary The use of ethyl oxamate for the synthesis of inorganic oxamato complexes is reported. A reaction system leading to the preparation of the novel polymeric -oxamato(-2) complexes [M(oxm)(H₂O)₂] _x (M=Cu, Zn, Cd), [Co(oxm)(H₂O)₂] _x ·0.5xH₂O and [Ni(oxm)(H₂O)₂] _x ·xH₂O is described (H₂ oxm = oxamic acid). Ethyl oxamate can also be used for the preparation of monomeric oxamato(-1) complexes.

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Der Einsatz von Ethyloxamat für die Synthese von Oxamato(-1) und neuen -Oxamato(-2)-Komplexen (Kurze Mitt.)

Zusammenfassung Es wird der Einsatz von Ethyloxamat für die Synthese von anorganischen Oxamato-Komplexen beschrieben. Ein Reaktions-System für die Herstellung von neuen -Oxamato(-2)-Komplexpolymeren: [M(oxm)(H₂O)₂] _x ; (M = Cu, Zn, Cd), [Co(oxm)(H₂O)₂] _x ·0.5xH₂O und [Ni(oxm)(H₂O)₂] _x ·xH₂O, wird vorgestellt. Ethyloxamat kann auch für die Herstellung von monomeren Oxamato(-1)-Komplexen verwendet werden.