Untersuchungen in den Systemen GeO2−Na2O, −K2O und −Rb2O

Zusammenfassung Die Systeme GeO₂–Na₂O, –K₂O und –Rb₂O werden röntgenographisch und differentialthermoanalytisch untersucht. Die früher beschriebene Verbindung Na₂Ge₄O₉ (I) erweist sich als identisch mit dem vonJ. F. White und Mitarbeitern angegebenen Na₄Ge₉O₂₀. Von der dargestellten isotypen Kalium-Verbindung werden die Gitterkonstanten ermittelt. Im analogen Rubidium-System läßt sich ein isotypes Enneagermanat bisher nicht nachweisen. Einkristallaufnahmen von Natriumtetragermanat [Na₂Ge₄O₉ (II)] ergeben eine hexagonale Elementarzelle mit 6 Formeleinheiten Na₂Ge₄O₉. Ebenso werden von den isotypen Kalium-und Rubidiumtetragermanaten die Gitterparameter bestimmt. Im Natrium-System stellt offensichtlich das Enneagermanat die stabile Phase dar, während das Tetragermanat nur durch rasches Abkühlen aus der Schmelze erhalten wird. Bei den Kaliumgermanaten ist dagegen das Tetragermanat die stabile Phase.Mit 2 Abbildungen     

Zur Kenntnis der Salpetersäure. X Methoden zur Gasanalyse im System N2−NO−NO2−N2O4−N2O3−HNO2−HNO3

Zusammenfassung Es werden vier Methoden zur Analyse einer Gasmischung N₂–NO–NO₂–N₂O₄–N₂O₃–HNO₂ besprochen und ihre Bedeutung für die Bestimmung der einzelnen Molekelarten kritisch auseinandergesetzt. Nach keiner der Methoden kann man den Gehalt an Salpetriger Säure und Salpetersäure neben den Oxyden des Stickstoffes auffinden. Aus diesem Grunde ist die Analyse der genannten Gasmischung nach den vier Methoden allgemein nicht genau durchführbar.Mit 1 Abbildung.Herrn Prof. Dr.A. Skrabal zum 75. Geburtstag gewidmet.     

Thermochemical investigations of the systems KCl−KBr−H2O,K2SO4−(NH4)2SO4−H2O and KNO3−NH4NO3−H2O at 298.15 K

For the equilibrium solid phases occurring in the systems: KCl?KBr?H₂O, K₂SO₄?(NH₄)₂SO₄?H₂O and KNO₃?NH₄NO₃?H₂O, the concentration dependencies of differential solution enthalpies, Δ_sol H ₂ for several crystallization paths, were measured. The limiting differential solution enthalpies, Δ_sol H ₂ ⁰ , were determined by extrapolation of the above dependencies to the ionic strength,I _m ⁰ , corresponding to the appropriate binary solutions. For KCl?KBr?H₂O system only, the clear dependence between Δ_sol H ₂ ⁰ andI _m ⁰ values was found and discussed.     

The Cl−NH3, Cl−H2O,F−NH3 and F−H2O clusters and their photoelectron spectra

The geometries of the Cl^–NH₃, Cl^–H₂O, F^–NH₃ and F^–H₂O clusters are optimized using the coupled cluster method. The four lowest ionization potentials are then calculated, leading to the ground and low excited states of the neutral species. The first three IPs describe ionization from the externalp state of the halogen atom, whereas the fourth corresponds to ionization from the NH₃ or H₂O moiety, leading to charge transfer complexes. These complexes were recently observed in the photoelectron spectrum of Cl^–NH₃, in full accord with our calculations.Supported in part by the U.S.-Israel Binational Science Foundation     

Solid potassium-conducting electrolytes in the K2 − 2x Ga2 − x V x O4 system

New potassium-conducting solid electrolytes based on potassium monogallate in the K_2?2x Ga_2?x V _x O₄ system are synthesized and studied. It is found that an introduction of V⁵⁺ ions leads to a considerable increase in the KGaO₂ conductivity due to the formation of vacancies in the potassium sublattice. The conductivity for optimal compositions is approximately 10^?3 S cm^?1 at 400°C and above 10^?2 S cm^?1 at 700°C. The results are compared with early obtained data for potassium monogallate dopped with four-charged cations.     

Reactivity of O2 − radical anions on hydrated ZrO2 surface

The concentration of O₂ ^? radical anions generated on the surface of hydrated ZrO₂ in an H₂O₂ solution was found to depend on H₂O₂ concentration. It was shown that this method can be used for detecting H₂O₂ in solutions at concentration as low as 0.01 wt%. The radical anions were found to react with organic molecules, even at room temperature. The decomposition kinetics of O₂ ^? radical anions was double-exponential with two reaction rate constants. The existence of two distinct rate constants suggests that two types of O₂ ^? radical anions with similar spectroscopic properties but different reactivity are present on the surface of hydrated ZrO₂. It is highly likely that different arrangements of hydroxyl groups near the radical anions account for the presence of the two types of O₂ ^? with different reactivity. The rate constants obtained in the presence of the organic compounds studied were found to conform with the expected order of reactivity: toluene > benzene ? hexane.     

Novel red-emitting phosphors, (Mg(1−x−y)MnxDyy)Al2Si2O8 and (Mg(1−x−y)MnxTmy)Al2Si2O8

Mn⁴⁺ doped and Dy³⁺, Tm³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the ²E → ⁴A₂ transitions of Mn⁴⁺.     

Phase-field Determination of NaSICON Materials in the Quaternary System Na2O−P2O5−SiO2−ZrO2: The Series Na3Zr3–xSi2PxO11.5+x/2

Two types of solid electrolytes have reached technological relevance in the field of sodium batteries: ß/ß”-aluminas and NaSICON-type materials. Today, significant attention is paid to room-temperature stationary electricity storage technologies and all-solid-state Na batteries used in combination with these solid electrolytes are an emerging research field besides sodium-ion batteries. In comparison, NaSICON materials can be processed at lower sintering temperatures than the ß/ß”-aluminas and have a similarly attractive ionic conductivity. Since Na₂O−SiO₂−ZrO₂−P₂O₅ ceramics offer wider compositional variability, the series Na₃Zr_3–xSi₂P_xO_11.5+x/2 with seven compositions (0≤x≤3) was selected from the quasi-quaternary phase diagram in order to identify the predominant stability region of NaSICON within this series and to explore the full potential of such materials, including the original NaSICON composition of Na₃Zr₂Si₂PO_l2 as a reference. Several characterization techniques were used for the purpose of better understanding the relationships between processing and properties of the ceramics. X-ray diffraction analysis revealed that the phase region of NaSICON materials is larger than expected. Moreover, new ceramic NaSICON materials were discovered in the system crystallizing with a monoclinic NaSICON structure (space group C2/c). Impedance spectroscopy was utilized to investigate the ionic conductivity, giving clear evidence for a dependence on crystal symmetry. The monoclinic NaSICON structure showed the highest ionic conductivity with an optimum ionic conductivity of 1.22×10⁻³ at 25 °C for the composition Na₃Zr₂Si₂PO₁₂. As the degree of P⁵⁺ content increases, the total ionic conductivity is initially enhanced until x=1 and then decreases again. Simultaneously, the increasing amount of phosphorus leads a decrease in the sintering temperatures for all samples, which was confirmed by dilatometry measurements. The thermal and microstructural properties of the prepared samples are also evaluated and discussed.     

Thermal magnetic investigation of the decomposition of NixMn1−xC2O4·2H2O

The systems Ni_xMn_1?xC₂O₄·2H₂O (x = 0.11, 0.34) are characterized by XRD, SEM, TG/DTA, EGA-MS and magnetic measurements. The last confirmed that the studied samples are real solid solutions. The SEM reveals that the morphology depends on both the excess of C₂O₄^2? and the initial ratio Ni/Mn. The thermal magnetic investigations (in situ) show that: (i) the presence of Ni in Ni_xMn_1?xC₂O₄·2H₂O leads to decreasing in the decomposition temperature in regard to that of the manganese oxalate; (ii) upon increasing the Ni content the temperature of decomposition (in air) is growing up; (iii) the presence of Ni stabilizes the manganese with respect to oxidation, in spite of the occurring process of decomposition.     

Oxidation with the “O2−H2O2—vanadium complex—pyrazine-2-carboxylic acid” reagent

The vanadium complex—pyrazine-2-carboxylic acid (PCA) system catalyzes oxidation of styrenes PhRC=CHR′ (R=H, Me; R′=H, Ph), or phenylacetylenes PhC=CR (R=H, Ph) with hydrogen peroxide in air to give aldehydes, ketones, and carboxylic acids. The reaction begins with H₂O₂ coordination to the vanadium ion followed by the formation of hydroxyl radicals. Catalytic action of PCA facilitates the reduction of the V^V complex to the V^IV complex and/or the stage of the formation of a peroxide derivative of vanadium.     

Peritektische Zersetzung von YBa2Cu3O7−x

During the heating of YBCO a peritectic reaction takes place at 1020C, which can be described by: 2YBa₂Cu₃O_7–xY₂BaCuO₅+L+(1-2x)/2O₂ (1) whereL = 3BaCuO₂ +2CuO is a fluid with limited amount of yttrium.It has been reported, that many parameters can influence the reaction. From one side not only the starting size of grains but also the heating rate have an influence on the resulting Y₂BaCuO₅-phase. From the other side, there is a change of the peritectical temperature caused by changing of the partial pressure of O₂ and the presence of parasitic phase.From general kinetic consideration one can draw the conclusion, that different mechanisms (nucleation, phase-boundary reaction and diffusion) can control the reaction.Using DTA/TG measurements, the peritectic reaction has been examined. Classical kinetic methods (Kissinger and Friedman) has been used. The Friedman method has given the dependence of the activation energy from reaction degree. This suggests many steps reactions. The dependence of the DTA-peaks from the heat rate suggest a parallel steps of reaction. This assumption can be motivated by evaluation of free O₂, one solid and liquid phase formation. Amount of this phases depends on the heating rate. Additionally X-ray and microscopic methods has been used. In this way was shown, that the perovskit structure is stable up to peritectical temperature and than is dramatically destroyed. From microscopic observations has been got information about shape and size of solid phase and it's creation as a function of temperature, time and starting grain size.

Die Arbeit wurde BMBF gefördert und durch Land NRW unterschtützt.     

Formation of O 2 − in charge transfer collisions of fast molecular hydrogen ions with O2 molecules

Cross sections for the production of O ₂ ^? in charge transfer collisions of fast molecular hydrogen ions (H ₂ ⁺ , D ₂ ⁺ , H ₃ ⁺ , and D ₃ ⁺ of 10 to 140 keV kinetic energy) with O₂ molecules have been determined by means of a time-of-flight mass spectrometer analysing the slow negative product ions from the collisions. Within the measuring accuracy equivelocity H ₂ ⁺ and D ₂ ⁺ ions have the same cross sections for the generation of O ₂ ^? . The projectile velocity dependence curve of the cross section passes through a broad maximum with a peak value of about 6.5×10^?18 cm² around the Bohr velocity (25 keV/u) before showing an asymptotic decrease still within the limited energy range under investigation that is in inverse proportion to the square of velocity. Throughout the examined energy range H ₃ ⁺ ions yield a cross section which is about 1.4 times larger than that of H ₂ ⁺ ions of the same velocity. The fragment ion O^? has been found to appear with cross sections between 10^?19 and 10^?18 cm² upon collisional excitation in the energy range under investigation, with ever decreasing intensity when the energy of the positive hydrogen ions, the proton included, was increased.     

Synthesis of Diaryl Ketones Catalyzed by Al2O3‐ZrO2/S2O8 2− Solid Superacid

Abstract

The acylation of a variety of aromatic compounds with benzoyl chloride or its derivatives and catalytic amounts of Al₂O₃–ZrO₂/S₂O₈ ^2? solid superacid affords the corresponding diaryl ketones in good to excellent yields 75–93% at appropriate temperature.     

Use of A Novel Acetone-H2O2−C10− Chemiluminescence System for the Determination of Iodide Ion

Abstract

The present paper reports a new chemiluminescence system, i.e, acetone-H₂O₂?C10^?, which can be catalyzed by iodide ion (I^?). Based on this catalysis, a new chemiluminescence method for the determination of trace iodide ion is proposed. the optimum conditions are reported in this note. the detection limit is 2 × 10^?11 g/ml I^?, the linear dynamic range is 4 × 10^?10 g/ml to 3 × 10^?7 g/ml I^?, and the variation coefficient at an iodide concentration of 5 × 10^?9 g/ml I^? (n=10) is 4.6%. the method has been satisfactorily applied to the determination of trace iodide ion in water.     

Electrochemical intercalation of O2− in CuAlO2 single crystal and photoelectrochemical properties

The delafossite CuAlO₂ single crystal, prepared by the flux method, is a low mobility p-type semiconductor with a hole mobility of 1.2 × 10⁻⁵ cm⁻² V⁻¹ s⁻¹. The chronoamperometry showed an electrochemical O²⁻ insertion with a diffusion coefficient D _303K of 3.3 × 10⁻¹⁸ cm² s⁻¹. The thermal variation of D in the range 293–353 K gave an enthalpy of diffusion (ΔH) of 44.7 kJ mol⁻¹. CuAlO₂ is photoactive, and the Mott–Schottky plot indicates a flat band potential of +0.42 V vs saturated calomel electrode and a holes density (N _A) of 10¹⁶ cm⁻³. The photocurrent spectra have been analyzed by using the Gartner model from which the absorption coefficients and diffusion lengths were determined. An optical transition at 1.66 eV, indirectly allowed, has been obtained. The spectral photoresponse provides a high absorption at 480 nm. The low quantum yield (η) is attributed to a small depletion length (440 nm) and a hole diffusion width (271 nm) compared to a very large penetration depth (12 μm).     

Single-molecule magnetism behavior of [Mn12O12(O2CR)16(H2O)4]2− salts

(PPh₄)₂[Mn₁₂O₁₂(O₂CCHCl₂)₁₆(H₂O)₄] (3) has been prepared by the two-electron reduction of [Mn₁₂O₁₂(O₂CCHCl₂)₁₆(H₂O)₄] (2) using iodide. Crystallization from CH₂Cl₂/hexanes yields a mixture of two crystal forms, 3·4CH₂Cl₂·H₂O (3a) and 36CH₂Cl₂ (3b), which are triclinic and monoclinic, respectively. They are both trapped valence 2Mn(II), 6Mn(III), 4Mn(IV). DC magnetization data for dried, unsolvated 3 in 1.80–4.00 K and 10–70 kG ranges were fit to give S=10, D=−0.28 cm⁻¹, g=2.00. Frequency-dependent out-of-phase (χ″_M) signals in AC susceptibility studies on crystalline sample of 3a and 3b combined with DC relaxation decay data were fit to the Arrhenius equation to give an effective energy barrier of U_eff=18.5 and 30.3 K, respectively. Magnetization vs. DC field sweeps on single crystals of 3a and 3b gave hysteresis loops containing steps due to quantum tunneling of magnetization (QTM). The step separations yielded ∣D∣/g values of 0.087 and 0.14 cm⁻¹, and consequently U=20 and 39 K (for g=2) for 3a and 3b, respectively, suggesting that the differences in U_eff are primarily caused by changes to D. This work demonstrates the sensitivity of the magnetic properties of [Mn₁₂]²⁻ single-molecule magnets to subtle differences in their environment.