Preparation and Properties of Highly Oriented Sr0.3Ba0.7Nb2O6 Thin Films by a Sol-Gel Process

We succeeded in the preparation of epitaxial or highly oriented strontium-barium niobate (Sr_0.3Ba_0.7Nb₂O₆) thin film by a sol-gel process. A homogeneous coating solution was prepared with Sr and Ba acetates and Nb(OEt)₅ as raw materials, and acetic acid and diethylene glycol monomethyl ether as solvents. Sr_0.3Ba_0.7Nb₂O₆ film sintered at 900°C on MgO(1 0 0) was oriented with c-axis perpendicular to the substrate surface. Sr_0.3Ba_0.7Nb₂O₆ film sintered at 700°C on SrTiO₃(1 0 0) was an epitaxial and oriented with c-axis in parallel to the substrate surface. Transmittance of Sr_0.3Ba_0.7Nb₂O₆ film (film thickness: 144 nm) was more than 60% at the range from 400 to 800 nm. Refractive index was 2.33 at 633 nm. Dielectric constant and dielectric loss of the Sr_0.3Ba_0.7Nb₂O₆ thin films prepared on polycrystal Pt substrates were 600 and 0.06 at room temperature and 1 kHz, respectively. The curie temperature (T_c) of polycrystalline Sr_0.3Ba_0.7Nb₂O₆ thin films was about 200°C. At room temperature and 50 kHz, remanent polarization (P_r) and coercive field (E_c) of the polycrystalline thin films were 1.79 C/cm² and 2.69 kV/cm, respectively.     

Crystallization and second harmonic generation in thermally poled niobium borophosphate glasses

Crystallization of glasses with compositions (1−x)(0.95 NaPO₃+0.05 Na₂B₄O₇)+xNb₂O₅, x=0.4, 0.43, 0.45, 0.48 was investigated by differential scanning calorimetry and X-ray powder diffraction. Crystallization of two phases was observed in the glasses with x=0.43-0.48. First phase is a sodium niobate with the structure of tetragonal tungsten bronze () and second phase is Na₄Nb₈P₄O₃₂ (). The crystallization of sodium niobate is correlated with increasing of nonlinear optical efficiency reported for thermally poled glasses with x>0.4. The results of Raman spectroscopy show the formation of three-dimensional (3D) niobium oxide framework in the glasses with increase of niobium concentration. This framework is supposed to have tetragonal tungsten bronze structure and to be responsible for nonlinear optical properties of the glass. Second harmonic generation signals of as prepared and crystallized glass after thermal poling are compared. The nucleation and crystallization do not improve the NLO properties of the glasses under study.     

Ion transport,ion extraction,and ion binding by synthetic cyclic octapeptide

Cyclic octapeptide, cyclo[Gly-L-Lys(Z)-Sar-L-Pro]₂, (CGLSP2) was synthesized as an ionophore model. Its ion-transport ability through a chloroform membrane was investigated in connection with ion extractability (K_ex) and conformational properties. CGLSP2 transported the picrate salts of Ba²⁺ and Ca²⁺ efficiently. The K_ex sequences were Ba²⁺>Ca²⁺Mg²⁺ and K⁺>Rb⁺>Na⁺, showing good agreement with the selectivity in ion transport. In addition, cation-binding properties of CGLSP2 to alkali and alkaline earth metal ion were investigated in acetonitrile by CD and NMR spectroscopy. Titration curves obtained from CD data revealed three kinds of CGLSP2/cation complexes. The values of 1:1 complex-formation constants (K₁) decreased in the order Ba²⁺>Ca²⁺>Mg²⁺>Li⁺Na⁺K⁺.¹H- and¹³C-NMR data showed that free CGLSP2 exists in at least five different conformational states in acetonitrile. After the addition of equimolar amounts of Ba(ClO₄)₂, these conformations converged into a single C₂-symmetric conformation with all-trans peptide bonds.     

A double-bonded niobium(III) compound with a formamidinate core: Nb2(μ-SMe)2(μ-DTolF)2 (η2-DTolF)2.2 toluene,DToIF= di-p-tolylformamidinate

The reaction of NaEt₃BH with Nb₂(-SMe₂)₃Cl₆ results in the transfer of a hydride ion to dimethylthioether with concomitant production of methane. Further reaction with potassium di-p-tolylformamidinate, KDTolF, yields Nb₂(-SMe)₂(-DTolF)₂²-DTolF:)₂.2 toluene, 1. In the latter, two thiomethoxide ions and two DTolF groups bridge the trivalent niobium atoms. Each of the other two DTolF groups chelate a metal atom to give the molecule an edge-sharing bioctahedral structure, The niobium-niobium distance of 2.655(2) A is consistent with the presence of a double bond between the metal atoms.     

1A1⇔5T2 Spin Transition in Heterometallic Solid Phases FexNi1-x(Htrz)3(NO3)2 · H2O (Htrz = 1,2,4‐Triazole)

Solid phases Fe_xNi_1-x(Htrz)₃(NO₃)₂ · H₂O (0.4 x 0.8$) and Ni(Htrz)₃(NO₃)₂ · H₂O were synthesized and studied. The phases were studied by means of magnetochemistry, powder Xray difraction analysis, and electronic and IR spectroscopy. The heterometallic phases are described by the stoichiographic method of differentiating dissolution (DD). The values of x were determined by two methods — atomic absorption and DD. Magnetochemical data showed that the solid phases exhibit a hightemperature ¹A₁ ⁵T₂ 0.5 x 0.8 and disappears at x = 0.4. The spin transition is accompanied by thermochromism (color changed from pink to white at 0.6 x 1 and from pink to light lilac at x = 0.5). A decrease in x leads to a decrease in the temperature of the forward (under heating T_c ) and reverse (under cooling T_c ) transitions, a decrease in hysteresis value ( T_c), and a smearing of the spin transition.     

Über hexagonale Perowskite mit Kationenfehlstellen. XXVIII. Die Struktur der rhomboedrischen 9 L-Stapelvarianten Ba3WNb□O9−x/2□x/2

On Hexagonal Perovskites with Cationic Vacancies. XXVIII. Structure of Rhombohedral 9 L Stacking Polytypes Ba₃W Nb □O_9?x/2□_x/2 According to the intensity calculations for Ba₃W_4/3Nb_2/3□O_26/3□_1/3 and Ba₃Nb₂□O₈□(II) these rhombohedral 9 L compounds crystallize in the space group R3m, sequence (hhc)₃. The refined, intensity related R′ values are 6.9% (Ba₃W_4/3Nb_2/3□O_26/3□_1/3) and 7.2% (Ba₃Nb₂□O₈□(II)). The relations between the rhombohedral 9 L structure (A₃M₂□O₉) and the palmierite type (A₃M₂□O₈□) are discussed.     

Enhanced dissolution and oral bioavailability of α-tocopheryl esters by dimethyl-β-cyclodextrin complexation

Inclusion complexation of heptakis (2,6-di-O-methyl)--cyclodextrin (DM--CyD) with -tocopheryl acetate and -tocopheryl nicotinate in aqueous solution was studied by the solubility method. The aqueous solubilities of the esters were about 10⁵ times increased by DM--CyD complexation. The phase-solubility diagram of the tocopheryl ester-DM--CyD systems showed a typicalA _p type, and the stability constants (K) of high-order complexes were estimated by analyzing the upward curvature of the diagrams. The solid complex of -tocopheryl nicotinate with DM--CyD in a molar ratio of 12 was prepared by the kneading method. The dissolution rate of the solid complex was much greater than that of the drug itself, and the rapidly dissolving form of -tocopheryl nicotinate, as an example, showed a markedly increased bioavailability (about 70-fold) after oral administration to fasted dogs.     

原位制备钛酸锶钡/铌酸锶钡复相陶瓷的研究

0引言驰豫型铁电陶瓷是近年来广泛研究和迅速发展的一种新型功能陶瓷[1]。通过把具有不同相变温度的驰豫型铁电体层层叠加,可以获得具有稳定的介电常数鄄温度关系的复合材料[2]。钛酸锶钡Ba1-xSrxTiO3和铌酸锶钡SrxBa1-xNb2O6都是重要的驰豫型铁电体,并且其居里温度均随Ba/Sr比     

Kinetics of thermal decomposition of barium zirconyl oxalate

Kinetics of the thermal decomposition of anhydrous barium zirconyl oxalate and a carbonate intermediate have been studied. Decomposition of the anhydrous oxalate, though it could be explained based on a contracting-cube model, is quite complex. Kinetics of decomposition of the intermediate carbonate Ba₂Zr₂O₅CO₃ is greatly influenced by thermal effects during its formation. (-t) curves are sigmoidal and obey a power law equation followed by first order decay. Presence of carbon in the vacuum-prepared carbonate has a strong deactivating effect. Decomposition of the carbonate is accompanied by growth in particle size of the product barium zirconate.

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Die Kinetik der thermischen Zersetzung von Barium-zirkonyl-oxalat

Zusammenfassung Es wurde die thermische Zersetzung von wasserfreiem Barium-zirkonyl-oxalat und dem intermediären Karbonat untersucht. Die Zersetzung des wasserfreien Oxalates ist — obwohl über das contracting-cube-Modell erklärbar — sehr komplex. Die Kinetik der Zersetzung des intermediären Karbonates Ba₂Zr₂O₅CO₃ ist stark von den thermischen Effekten während seiner Bildung abhängig. Die (-t)-Kurven gehorchen einem exponentiellen Gesetz, gefolgt von einem Zerfall erster Ordnung. Die Gegenwart von Kohlenstoff im Karbonat hat einen starken desaktivierenden Effekt. Die Zersetzung des Karbonats wird von einem Wachstum der Partikelgröße des Produktes (Bariumzirkonat) begleitet.

     

High-Pressure Synthesis of Fully Occupied Tetragonal and Cubic Tungsten Bronze Oxides

A high-pressure reaction yielded the fully occupied tetragonal tungsten bronze K₃W₅O₁₅ (K_0.6WO₃). The terminal phase shows an unusual transport property featuring slightly negative temperature-dependence in resistivity (dρ/dT<0) and a large Wilson ratio of R_W=3.2. Such anomalous metallic behavior possibly arises from the low-dimensional electronic structure with a van Hove singularity at the Fermi level and/or from enhanced magnetic fluctuations by geometrical frustration of the tungsten sublattice. The asymmetric nature of the tetragonal tungsten bronze K_xWO₃-K_0.6−yBa_yWO₃ phase diagram implies that superconductivity for x≤0.45 originates from the lattice instability because of potassium deficiency. A cubic perovskite KWO₃ phase was also identified as a line phase—in marked contrast to Na_xWO₃ and Li_xWO₃ with varying quantities of x (<1). This study presents a versatile method by which the solubility limit of tungsten bronze oxides can be extended.     

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.     

Zur Totalsynthese von Human-Sekretin

Summary The synthesis of the heptacosapeptide amide with the primary structure of Human-secretin is described. For this purpose 7 fragments were designed, i.e. H-Gly-Leu-Val-NH₂ 25–27b,Z-Arg(Z ₂)-Leu-Leu-Gln-OH 21–24,Z-Arg(Z ₂)-Leu-Gln-OH 18–20,Z-Arg(Z ₂)-Glu(OtBu)-Gly-Ala-OH 14–17,Z-Arg(Z ₂)-Leu-OH 12–13,Z-Thr(tBu)-Ser(tBu)-Glu(OtBu)-Leu-Ser(tBu)-OH 7–11,Adoc-His(Adoc)-Ser(tBu)-Asp(OtBu)-Gly-Thr(tBu)-Phe-OH 1–6 these fragments were consequently assembled to the overall protected total sequence using the Wünsch/Weygand-method with dicyclohexylcarbodiimide. After deprotection by exposure to trifluoroacetic acid in presence of 1,2-ethanedithiol and water as scavenger, the isolated crude product was purified by column chromatography on CM-Sepharose, fast flow. This synthetized Human-secretin showed the full biological activity in comparison to Porcine-secretin.

Herrn Prof. Dr. E. Bayer zum 65. Geburtstag gewidmet.     

Some A6B5O18 cation-deficient perovskites in the BaO-La2O3-TiO2-Nb2O5 system

Some dielectric oxides have been synthesized and characterized in the BaO-La₂O₃-TiO₂-Nb₂O₅ system. Through Rietveld refinement of X-ray powder diffraction data, Ba₅LaTi₂Nb₃O₁₈ and Ba₄La₂Ti₃Nb₂O₁₈ are identified as the A_nB_n−1O_3n (n=6) type cation-deficient perovskites with space group and lattice constants , and for Ba₅LaTi₂Nb₃O₁₈; , and for Ba₄La₂Ti₃Nb₂O₁₈, respectively. Their ceramics exhibit high dielectric constant up to 57 and high quality factors (Qf) up to 21,273 GHz. The temperature coefficient of resonant frequency (τ_f) of these ceramics is decreased with the increase of B-site bond valence.     

Synthesis and properties of mullite and cordierite aerogels

This work deals with the preparation of aluminosilicate aerogels, especially mullite (3Al₂O₃·2SiO₂) and cordierite (2MgO·2Al₂O₃·5SiO₂) aerogels, from the cohydrolysis of tetraethoxysilane and chelated aluminum-secbutylate; in the case of cordierite magnesium nitrate was added. The influence of various preparation conditions on the aerogel synthesis is described. Crystallization and sintering behavior of mullite aerogels supercritically dried in acetone or alcohol differs from that one of mullite aerogels dried in CO₂. During non-isothermal heat treatment the former show a drastically reduced shrinkage compared to the latter. This behavior can be explained by a phase separation during the high temperature autoclaving process. In cordierite aerogels the crystallization of tetragonal mullite at about 1000°C is observed, while the correspondent xerogels show the crystallization of - and - cordierite between 1000 and 1100°C. On the other hand sintering is promoted in cordierite aerogels, which is due to the content of MgO.     

Diacetylenic Derivatives of Fe2(CO)6(μ-EE′): Spectroscopic Investigations of Fe2(CO)6{μ-EC(H) = C(C≡ CMe)E′} (E = E′, E ≠ E′; E, E′ = S, Se, Te)

The diacetylenic adducts, Fe₂(CO)₆{-EC(H) = C(C CMe)E} (E = E, E E; E, E = S, Se, Te) (1–8) have been obtained from the room temperature stirring of Fe₂(CO)₆(-EE) with HC CC CMe in methanol solvent containing sodium acetate. Compounds 1–8 have been characterized by IR and multinuclear NMR (¹H, ¹³C, ⁷⁷Se, and ^l25Te) spectroscopy. Trends in the chemical shifts of ⁷⁷Se and ¹²⁵Te NMR spectra of Fe₂(CO)₆{-EC(H) = C(C CMe)E} with a variation of EE are discussed.     

Rare-Earth Substituted Polyoxoanions: [{La(CH3COO)(H2O)2(α2-P2W17O61)}2]16− and [{Nd(H2O)3(α2-P2W17O61)}2]14−

The lanthanum-substituted polyoxometalate [{La(CH₃COO)(H₂O)₂( ₂-P₂W₁₇O₆₁)}₂]^16– (1) and the neodymium-substituted species [{Nd(H₂O)₃( ₂ -P₂W₁₇O₆₁)}₂]^14– (2) have been synthesized and characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray analysis was carried out on K₁₆[{La(CH₃COO)(H₂O)₂( ₂ -P₂W₁₇O₆₁)}₂]36H₂O, which crystallizes in the triclinic system, space group P¯1, with a=12.3863(6) Å, b=12.8934(6) Å, c=31.7285(14) Å, =84.2000(10)°, =81.2300(10)°, =61.6500(10)°, and Z=1; K_6.5Nd_2.5[{Nd(H₂O)₃( ₂-P₂W₁₇O₆₁)}₂]55H₂O, which crystallizes in the monoclinic system, space group P2 ₁ /n, with a=17.5030(9) Å, b=23.7842(12) Å, c=19.1869(10) Å, =100.6610(10)°, and Z=1. The head-on, trans-oid dimer 1 consists of two ( ₂ -P₂W₁₇O₆₁)^10– fragments connected by a lanthanum-acetate dimer, (La₂(CH₃COO)₂(H₂O)₄)⁴⁺. Each La³⁺ ion is nine-coordinated in a monocapped, square-antiprismatic fashion. The neodymium-derivative 2 is also a trans-oid dimer, but the mode of binding is different from 1 and is best described as side-on. Each Nd³⁺ ion is eight-coordinated in a square-antiprismatic fashion with three terminal water molecules.     

Phase diagram in the Bi-Pb-Sr-Ca-Cu-O system

TG-DTA and X-ray diffraction measurements at different temperatures and under different oxygen partial pressures were carried out on the species Bi_1.6Pb_0.4Sr₂CuO_6±x, Bi_1.6Pb_0.4Sr₂CaCu₂O_8±y and Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10±z to analyse the influence of the oxygen chemical potential on the phase transformations. A new phase was found at isobaric invariant equilibrium for 0.5 /P_Tot1 at 884°C. This new phase presents a buffer effect towards oxygen exchange between superconducting oxides and the gas phase.This work has benefited from partial financial support by the Centre National d'Etudes Spatiales (C.N.E.S.). It is a pleasure to thank Prof. Yasuhiko Syono of Tohoku University - Sendai- Japan for valuable discussions.     

Chemical properties of positive singly charged astatine ion in aqueous solution

The mobility of oxidized astatine in solutions H(Na)ClO₄ (=0.4 M) – 1·10^–4M K₂Cr₂O₇ has been measured at 25°C in the interval 0.63pH1.68. Under these conditions astatine migrates to the cathode only. The speed of the migration depends upon the concentration of hydrogen ions in solution: pH 1.68 U_c = 1.17 · 10^-4 cm² V^-1 s^-1 pH 0.63 U_c = 2.67 · 10^-4 cm² V^-1 s^-1 The effect agrees with the opinion that the singly charged cation of astatine formed in acidic solutions is a strong aquacomplex [(H₂O)_xAt]⁺ (x=1–2) (protonated hypoastatic acid). Deprotonation constant of this cation is K_dp=0.032±0.005. Specific properties of the astatine cation are given. They can be explained, probably, through the peculiarities of its structure.     

Unusual condensation of propargylamine. Generation of the 1,3-di(propargylimino)propane anion coordinated to the cobalt(iii) atom

The reaction of propargylamine with the hexanuclear complex Co^II ₆(₃-OH)₂(OOCCMe₃)₁₀(HOOCCMe₃)₄ or the polymer [Co(OH)_n(OOCCMe₃)_2–n]_x under an argon atmosphere afforded the unstable paramagnetic tetramine complex Co^II(OOCCMe₃)₂(H₂NCH₂CCH)₄ (1). In air, if an excess of propargylamine is present, the latter complex is transformed into the complex Co^III(OOCCMe₃)₂(NH₂CH₂CCH)₂[²-N,N"-(HCCCH₂N=CHCHCH=N—CH₂CCH)] (2) containing a new ligand, viz., the 1,3-di(propargylimino)propane anion, which is a formal analog of the acetylacetonate anion. In contrast to propargylamine, 1,3-diaminopropane reacted with the Co^II trimethylacetate clusters in air to produce the cationic complex [Co^III{1,3-(NH₂)₂(CH₂)₃}₂(OOCCMe₃)₂]⁺OOCCMe₃ ^– (3) without entering into condensation reactions. The structures of the resulting complexes were determined by X-ray diffraction analysis.