Katharina Gibson

Syntheses of the Bi(Pb)-2212 high-Tc superconductor through a novel oxide nitrate route

A novel route is presented for the syntheses of Bi2Sr2CaCu2Ox (Bi-2212) and (Bi,Pb)2Sr2CaCu2Ox (Bi,Pb-2212). Mixtures of oxides, nitrates and carbonates with approximate 2:2:1:2 metal ion compositions are dissolved in HNO3 and dried at 200 °C in air. Afterwards they are reacted under their in situ generated NOx atmosphere in a closed reactor (Staurohr). This reaction forces the system to form the nitrate precursors (Bi,Sr,Ca)2O2NO3/CuO and (Bi,Pb,Sr,Ca)2O2NO3/CuO, respectively. In the final reaction stage these mixtures are converted into Bi(Pb)-2212 under NOx discharge in air. All important reaction stages and phase compositions are analysed by means of powder XRD.

NOx control of the Bi-2201 formation

Abstract A novel synthetic concept is presented for the synthesis of Bi 2 Sr 2 CuO x (Bi-2201). Metal nitrates of Bi 3+ , Sr 2+ , and Cu 2+ are mixed in 2:2:1 molar ratio and molten with their own crystal water to form a homogeneous mixture. After release of crystal water and some NO x , the solid mixture is treated through a process in which NO x controls the reactivity of the system. This reaction stage forces the system to form of a homogeneous BiSrO 2 NO 3 /CuO precursor mixture in approximate 2:1 molar ratio. Finally, the precursor mixture is being converted into Bi-2201 under continuous release of NO x . This synthetic route provides complete conversions, high reproducibilities, and yields a reliable standard material.

NH4CaCl3, die reaktive Zwischenstufe in einer Synthese von CaCl2

Wasserfreies CaCl2 entsteht bei der Reaktion von CaCO3 mit NH4Cl. Die Reaktion verlauft uber ein Zwischenprodukt, das als NH4CaCl3 charakterisiert wird. Es kristallisiert im GdFeO3-Typ und zersetzt sich bei hoheren Temperaturen zu CaCl2 und NH4Cl. Bildung und Zerfall des Zwischenproduktes sowie die Entstehung von CaCl2 wurden rontgenographisch und thermoanalytisch verfolgt. NH4CaCl3, the Reactive Intermediate Phase in a Synthesis of CaCl2 The reaction of CaCO3 with NH4Cl leads to formation of CaCl2. In this reaction an intermediate phase is formed, that is be characterized as NH4CaCl3. This intermediate phase crystallizes in the GdFeO3 type and decomposes at elevated temperatures to yield CaCl2 and NH4Cl. The formation and the decomposition of this intermediate phase as well as the formation of CaCl2 were studied with X-ray and thermoanalytical methods.

Synthesis, Structure, and Decomposition of (NH4)2[Mo6Cl14] · H2O

(NH4)2[Mo6Cl14] · H2O (1) was prepared from reactions of MoCl2 in ethanol with aqueous NH4Cl solution. It crystallizes in the monoclinic space group I2/a (no. 15), Z = 4 with a = 912.3(1), b = 1491.2(2), c = 1724.8(2) pm, β = 92.25(1)°; R1 = 0.023 (based on F values) and wR2 = 0.059 (based on F2 values), for all measured X-ray reflections. The structure of the cluster anion can be given as [(Mo6Cl)Cl]2– (i = inner, a = outer ligands). Thermal stability studies show that 1 loses crystal water followed by the loss of NH4Cl above 350 °C to yield MoCl2. The water-free compound (NH4)2[Mo6Cl14] (2) was synthesized by solid state reaction of MoCl2 and NH4Cl in a sealed quartz ampoule at 270 °C. No single-crystals could be obtained. Decompositions of 1 and 2 under nitrogen and argon exhibited the loss of NH4Cl at about 350 °C. Decomposition under NH3 resulted in the formation of MoN and Mo2N at 540 °C and 720 °C, respectively. Synthese, Struktur und Zersetzung von (NH4)2[Mo6Cl14] · H2O (NH4)2[Mo6Cl14] · H2O (1) wurde aus MoCl2 in Ethanol mit wassriger NH4Cl-Losung dargestellt und kristallisiert (monoklin, Raumgruppe I2/a (Nr. 15), Z = 4 mit a = 912.3(1), b = 1491.2(2), c = 1724.8(2) pm, β = 92.25(1)°; R1(F) = 0.023, wR2(F2) = 0.059 fur alle gemessenen Reflexe). Die Struktur der Cluster-Anionen kann als [(Mo6Cl)Cl]2– (i = innerer, a = auserer Ligand) beschrieben werden. Beim Erhitzen gibt 1 das Kristallwasser ab. Oberhalb von 350 °C entweicht NH4Cl und es bildet sich MoCl2. Wasserfreies (NH4)2[Mo6Cl14] (2) konnte durch Erhitzen von MoCl2 und NH4Cl auf 270 °C in einer evakuierten, zugeschmolzenen Quarzglasampulle dargestellt werden. Einkristalle konnten bisher nicht erhalten werden. Bei der Zersetzung von 1 und 2 unter Stickstoff oder Argon wird NH4Cl bei etwa 350 °C abgegeben. Die Zersetzung unter NH3 ergab MoN und Mo2N bei 540 °C bzw. 720 °C.