Synthesis and conductivities of the apatite-type systems, La9.33+xSi6−yMyO26+z (M=Co, Fe, Mn) and La8Mn2Si6O26

Apatite-type oxides of formula (La/Sr)_10−xSi₆O_26+y have been attracting significant interest recently, because of their high oxide ion conductivity. In this paper we report the synthesis and conductivities of phases based on doping La_9.33Si₆O₂₆ with Co, Fe, Mn on the Si site, according to the formula La_9.33+x/3Si_6−xM_xO₂₆ (M=Co, Fe, Mn). Substitution limits observed were x≤1.5 (Co), x≤1.25 (Fe), x≤0.5 (Mn). Higher Mn levels could be achieved by substituting onto the La site, with it being possible to prepare the phase La₈Mn₂Si₆O₂₆. The highest conductivities were observed for the Co doped samples, although investigations into the dependence of conductivity on p(O₂) (0.2–10⁻⁵ atm.) indicated that the conductivity was dominated by the electronic component in these cases. In contrast, the conductivities for the Fe and Mn doped samples were mainly ionic in the same p(O₂) range. Experiments into varying the oxygen content of these doped phases indicated that increasing the oxygen content above the nominally stoichiometric O₂₆ appears to increase the oxide ion conductivity. Preliminary studies of the reactivity of the electrolyte La_9.33Si₆O₂₆ with potential SOFC cathode materials (La_1−xSr_xMO₃; M=Co, Fe, Mn) suggests that reaction can occur at high temperatures leading to the incorporation of the transition metal into the apatite electrolyte. However, the fact that these doped phases exhibit high conductivities suggests that this may limit any problems caused by such a reaction at the electrolyte-electrode interface. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Über die Synthese des Muscaflavins. Vorläufige Mitteilung,

Synthesis of muscaflavin A biomimetic type synthesis of the yellow dihydroazepine amino acid 5 isolated from fly agaric is achieved starting with carboxypyridyl alanine derivatives.     

Inclusive photon and π0 production inK + p interactions at 70 GeV/c

Inclusive and semi-inclusive cross sections and distributions of γ's and π⁰'s inK ⁺ p interactions at 70 GeV/c are presented. The results are compared to other experiments and to the Lund model for low-p _T hadron collisions.     

Mechanismus der basischen hydrolyse von oligopeptid-4-nitro-aniliden

Oligopeptide-4-nitroanilide alkaline hydrolysis mechanism has been studied in a wide pH-range. In the log k_b vs pH-profile we have identified three different ranges. In the $\text{k}{}_2\text{k}{}_{-1}$ controlled range a stereoelectronic control of the cleavage of the tetrahedral intermediate has been observed m the case, a α-substituent is available for interaction with groups on the tetrahedral carbon atom. In the k₃/k_-1- and in the k₁-range of the hydrolysis no mechanistically differences exist between oligopeptide-4-nitroanilides and acet-4-nitroanilides. Kinetic-D-isotope effects are consistent with the postulated mechanism of hydrolysis.     

A 94/47 GHz frequency halver using a GaAs Gunn device

This paper describes the basic principles and the set up of a new kind of frequency halvers suited for millimeter wave applications. A Ga As Gunn-device is used to act like a nonostable multivibrator having a hold time adequate to the domain transit time T_t of the Gunn-device.In a certain frequency range depending on the transit frequency f_T=1/T_T, bias voltage and circuit parameters a harmonic wave synchronized fundamental/2nd harnonic mode oscillator is able to perform as a frequency halver. An input power of only 1mW is sufficient to achieve a bandwidth of 5 GHz respectively 2.5 GHz centered around 94 GHz respectively 47GHz. Since the output power is 50 mW at fundamental frequency f_F, this halver offers 17dB conversion gain.     

Aufschluß von Niob durch Chlorierung und Abtrennung der Spurenverunreinigungen von der Matrix durch homogene Fällung

Analytical and Bioanalytical Chemistry - Das Verhalten der Spurenelemente Au, Cd, Co, Cu, Fe, Ir, La, Mn, Na, Sb, Se, Ta, W und Zn wurde bei der Chlorierung der Niob-Matrix im Cl2-Strom, und...