Das Ternare System Nb2O5-Li2O-Sc2O3

Zusammenfassung Es wird ein isothermer Schnitt im System Nb₂O₅ -Li₂O-Sc₂O₃ untersucht. Dabei wurde die neue Verbindung Li_0.5Sc_0.5Nb₂O₆ gefunden. Die Röntgenreflexionsaufnahmen ergaben unter Annahme eines orthorhombischen Gitters die Parameter a=1433.6/2/ pm, b=572.96/6/ pm und c=505.76/4/ pm.Bei 1453 K wurde der LiNbO₃-Homogenitätsbereich bestimmt, der sich vom binären System Li₂O-Nb₂O₅ bis zu 5 mol% Sc₂O₃ im Dreikomponentensystem erstreckt. Im Homogenitätsbereich wurde die Variation der Gitterkonstanten gemessen. Das Volumen der Elementarzelle nimmt mit steigendem Sc₂O₃-Gehalt zu.

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An isothermal section was investigated in the system Nb₂O₅-Li₂O-Sc₂O₃. The new compound Li_0.5Sc_0.5Nb₂O₆ was found The x-ray reflection pattern could be indexed with the assumption of an orthorhombic lattice with the parameters of a=1433.6(2) pm, b=572.96(6) pm, c=505.76(4) pm.The LiNbO₃-homogeneity range was determined at 1453 K. It extends from the binary Li₂O-Nb₂O₅ to 5 mole-% Sc₂O₃ in the ternary system. The variation of the lattice constants of LiNbO₃ was measured in the homogeneity range. The volume of the unit cell increases with increasing content of Sc₂C₃.

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Nb₂O₅-Li₂O-Sc₂O₃, Li_0,5 Sc_0,5Nb₂O₆. , $ = 1433,6/2/ , =572,96/6/ =505,76/4/ . 1453 LiNbO₃, $ Li₂O-Nb₂₅ $ 5 %. $ . .

     

Perovskite solid solutions in the BaO-CuO-Y2O3-Nb2O5 system

Freeze dried complex carboxylates are highly reactive precursors for complex perovskite solid solutions in the system BaO-CuO-Y₂O₃-Nb₂O₅ On thermal decomposition of the amorphous precursors the formation of complex crystalline phases begins at 600 °C. In most cases the themodynamically controlled phase composition is reached after a reaction time of two hours at about 900 °C. Beginning from the perovskite compound Ba₂YNbO₆ a partial substitution of Y by Cu or by a combination 2/3 Cu,1/3 Nb leads to extended fields of solid solutions with cubic perovskite structure. Substitution according to Y_0,5xBa₂(Y_1-0,5xCu_xNb)O_6+x is limited to x ≤ 0,4. A compound LBa₂Cu₂NbO₈ (x=2), well characterized for L=La, does not exist for L=Y. The composition of solid solutions depends on the preparation conditions. There are some signs for an inhomogeneous distribution of B-cations in the cubic perovskites.     

Photoelectrochemical properties of Fe2O3-Nb2O5 films prepared by sol-gel method

Fe2O3-Nb2O5 coating films of various Nb/(Fe + Nb) mole ratios were prepared on nesa silica glass substrates from Fe(NO3)3.9H2O - NbCl5 - CH3(CH2)2CH2OH - CH3COOH solutions by the sol-gel method. The photoanodic properties were studied in a three-electrode cell with an aqueous buffer solution of pH = 7 as the supporting electrolyte. The crystalline phases identified were alpha-Fe2O3 (Nb/(Fe + Nb) = 0), alpha-Fe2O3 + FeNbO4 (Nb/(Fe + Nb) = 0.25), FeNbO4 (Nb/(Fe + Nb) = 0.5), FeNbO4 + Nb2O5 (Nb/(Fe + Nb) = 0.75), and Nb2O5 (Nb/(Fe + Nb) = 1). When the Nb/(Fe + Nb) mole ratio increased from 0 to 0.25, the crystalline phases changed from alpha-Fe2O3 to alpha-Fe2O3 + FeNbO4, the photoanodic current under white light illumination increased, and the photoanodic current under monochromatized light illumination increased in both visible and ultraviolet regions. When the Nb/(Fe + Nb) ratio increased over 0.25, the crystalline phases changed to FeNbO4, FeNbO4 + Nb2O5, or Nb2O5, and the photoanodic current decreased. The sample consisting of alpha-Fe2O3 and FeNbO4 (Nb/(Fe + Nb) = 0.25) exhibited photoresponse extending to 600 nm and an IPCE of 18% at a wavelength of 325 nm.     

Structure and polymorphism of complex phosphates prepared from fluxes of the Na2O-P2O5-Fe2O3-Nb2O5 system

The phase formation of complex phosphates in the Na₂O-P₂O₅-Fe₂O₃-Nb₂O₅ flux system was studied in the ranges of sodium-to-phosphorus ratios of 0.7–1.2 and iron-to-niobium ratios of 0.9–2.7. The crystallization region and crystallization conditions for the compounds of composition Na_3?2x Fe_2-x Nb_x(PO₄)₃ (0.8 ≤ x < 1.2) were found. These compounds can be prepared in two (hexagonal and monoclinic) polymorphs. Single-crystal X-ray diffraction experiments were carried out for hexagonal NaFeNb(PO₄)₃ (space group $R\bar 3$ c, a = 8.590 Å, c = 22.013 Å). The polymorphism in Na_3-2x Fe_2-x Nb_x(PO₄)₃ complex phosphates is considered as dependent on the preparation parameters.     

A Study of Evaporation in the TiO2-Nb2O5 Oxide System by High-Temperature Mass-Spectrometry

High-temperature mass-spectrometry was applied to study the vapor phase composition and dynamics of its variation in evaporation of oxide materials of the system TiO₂-Nb₂O₅. The incongruent nature of evaporation processes is established.     

Das System Ca(N3)2-H2O

Zusammenfassung Das Zustandsdiagramm für das System Ca(N₃)₂-H₂O wird auf Grund von Gefrierpunkts- und Löslichkeitsmessungen auf-gestellt. Ferner werden Lösungswärmen bestimmt und Dampfdruckmessungen vorgenommen. Durch Aufstellen eines Kreisprozesses werden die Normalbildungsenthalpien folgender Verbindungen bestimmt: Ca(N₃)₂, Ca(N₃)₂·0,5 H₂O, Ca(N₃)₂·1,5 H₂O und Ca(N₃)₂·4 H₂O.

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The system Ca(N₃)₂-H₂O

Based on measurements of freezing points and solubility the phase diagram of the system Ca(N₃)₂-H₂O is given. Furthermore, investigations on the heat of solution and measurements of the vapor pressure were carried out. By setting up a cycle process the standard enthalpies of formation for the following compounds were determined: Ca(N₃)₂, Ca(N₃)₂·0,5 H₂O, Ca(N₃)₂·1,5 H₂O and Ca(N₃)₂·4 H₂O.

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Mit 2 Abbildungen     

SnO2-Nb2O5/MgAl2O4/α-Al2O3催化环氧乙烷水合制乙二醇

采用水热稳定的MgAl2O4尖晶石对-αAl2O3载体表面进行修饰,采用具有较强亲水性能的SnO2对活性组分Nb2O5进行修饰,制备了SnO2-Nb2O5/MgAl2O4/-αAl2O3催化剂,并用于环氧乙烷水合制乙二醇反应.采用X射线衍射、红外光谱和程序升温脱附研究了Sn/Nb摩尔比对催化剂酸性、环氧乙烷在催化剂表面的吸附状态和吸附强度以及催化剂性能的影响.结果表明,Sn/Nb摩尔比明显影响催化剂的组成和结构;催化剂的结构不同,环氧乙烷在催化剂表面的吸附强度存在明显差别,催化剂的催化性能明显不同.     

Spectroscopic properties and thermal stability of Er3+ -doped TeO2-B2O3-Nb2O5-ZnO glass for potential WDM amplifier

A series of novel 70TeO2-(15-x)B2O3-xNb2O5-15ZnO-1wt.% Er2O3 (TBN x=0, 3, 6, 9, 12 and 15 mol%) tellurite glasses were prepared. The thermal stability, absorption spectra, emission spectra, and the lifetime of the (4)I(13/2) level of Er(3+) ions were measured and investigated. Three Judd-Ofelt intensity parameters Omega(t) (t=2, 4 and 6) (Omega(2)=(5.42-6.76)x10(-20)cm(2); Omega(4)=(1.37-1.73)x10(-20)cm(2); Omega(6)=(0.70-0.94)x10(-20)cm(2)) of Er(3+) ions were calculated by Judd-Ofelt theory. It is found that the Omega(6) first increases with the increase of Nb2O5 content from 0 to 6 mol% and then decreases, which is mainly affected by the number of non-bridging oxygen ions of the glass network. The high peak of stimulated emission cross-section (sigma(e)(peak)=(0.77-0.91)x10(-20)cm(2)) of Er(3+): (4)I(13/2)-->(4)I(15/2) transition were obtained according to McCumber theory and broad full width at half maximum (FWHM=65-73 nm) of the (4)I(13/2)-->(4)I(15/2) transition of Er(3+) ions were measured. The results indicate that these new TBN glasses can be used as a candidate host material for potential broadband optical amplifiers.     

Ferromagnetic and dielectric properties of lead free KNbO3-CoFe2O4 composites

Multiferroic (1-x)KNbO₃-(x)CoFe₂O₄ (x = 0.0, 0.25, 0.5, 0.75 and 1.0 mol) composites were prepared by solid state reaction method. X-ray diffraction results showed that the prepared (1-x)KNbO₃-(x)CoFe₂O₄ composites belong to orthorhombic system for x = 0.0 (perovskite KNbO₃), cubic system for x = 1.0 (spinel CoFe₂O₄) and mixed phase of KNbO₃ and CoFe₂O₄ for x = 0.25, 0.5 and 0.75. Nb-O and Fe-O stretching vibrational modes were observed in the Fourier transform and Raman spectral analyses, respectively. The HR-SEM analysis showed that the morphology of KNbO₃ and CoFe₂O₄ composites was significantly modified by CoFe₂O₄ content. Energy dispersive X-ray spectroscopy results confirmed the presence of K, Nb, Fe, Co and O in (1-x)KNbO₃-(x)CoFe₂O₄ composites. The ionic state of Nb, Co, Fe and O was examined by X-ray photoelectron spectroscopy analysis. The high value of coercivity (H_c = ∼981Oe) for x = 0.5 and the enhanced dielectric constant for x = 0.5 and 0.75 were observed.     

Das thermische Verhalten von Na5[Fe(CN)5SO3]·2H2O

The thermal behaviour of Na₅[Fe(CN)₅SO₃]·2H₂O has been investigated by thermogravimetric and differential thermal analysis. Detailed studies of the decomposition residues using various physicochemical methods show that decomposition occurs in a manner similar to that previously postulated for related compounds.     

Studies on the System ZnO-V2O5-Fe2O3 Reactivity of ZnFe2O4 Towards ZnV2O6

Studies on the reactivity of ZnFe₂O₄ towards ZnV₂O₆ revealed that in the solid state the phases interact in a molar ratio of 1:3 to form a new compound, to which the molecular formula Zn₂FeV₃O₁₁ was assigned. The compound melts congruently at 825±5°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

四氧化二氮-五氧化二氮-硝酸体系组成的分析

1引言N2O5作为新型硝化剂受到广泛的关注。N2O4电解氧化制N2O5过程中,在阳极得到N2O4、N2O5和HNO3的混合物,因此需要对N2O4-N2O5-HNO3体系进行分析。由于N2O4、N2O5和HNO3的结构相似,这给拉曼光谱等光谱分析方法定量分析此体系带来很大的困难。本实验采用简单经济的滴定法,并用     

Das Thermische Verhalten von Na3[Fe(CN)5SO(CH3)2] · H2O

The thermal behaviour of Na₃ [Fe(CN)₅SO(CH₃)₂] · 2H₂O has been investigated by thermogravimetry and diferential thermal analysis. The results are briefly discussed.     

La3F3[Si3O9]: Das erste Fluoridsilicat aus dem ternären System LaF3/La2O3/SiO2

La₃F₃[Si₃O₉]: The First Fluoride Silicate in the Ternary System LaF₃/La₂O₃/SiO₂ By reacting La₂O₃ with LaF₃ and SiO₂ (silica gel) using CsCl as a flux (molar ratio 1 : 1 : 3 : 6; 700 °C, 21 d) it was possible to obtain single crystals of La₃F₃[Si₃O₉] (hexagonal, space group: P 6 2c (no. 190); a = 708.32(3), c = 1089.48(6) pm; Z = 2) as colourless, hexagonal platelets. The crystal structure comprises discrete cyclic [Si₃O₉]^6– anions of three corner-linked [SiO₄] tetrahedra along with a graphite-like network of the composition {[LaF_3/3]²⁺}. Shorter reaction times even produced single crystals of tysonite-type LaF₃ (trigonal, space group: P 3 c1 (no. 165); a = 718.80(6), c = 735.94(6) pm; Z = 6) on which a X-ray structure analysis was achieved, too. The structures of both compounds, each of which show an elevenfold anionic coordination (CN = 9 + 2) for the La³⁺ cations, are compared. The influence of the reactivity of the educts and the temperature on the reaction as well as the difficulties in the X-ray differentiation of fluorine and oxygen will be discussed.