Preparations Under Flowing Oxygen

Syntheses of near-single phases of the lead-substituted thallium monolayer phases with up to 6 Cu-O layers i.e., Pb-doped 1212, 1223, 1234, 1245, and 1256, have been recently reported (21). Reactant mixtures of various proportions of Tl2Os, PbO, CaO, Ba02, and CuO were pelletized, wrapped in gold foil, and sintered at 860-900°C under flowing oxygen for 10-30 h. The Tc value reached a maximum of 121 K for the 1234 compound and declined with further increase in the number of Cu-O layers. X-ray powder diffraction data for the different phases were refined using the Rietveld method and a consistent increase in the c-axis accompanied the increase in number of Cu-O layers. 

A review of the synthetic methods used to prepare the bismuth and thallium families of cuprate superconductors has been presented. An overview of our current knowledge of phase relationships in the bismuth systems is also given such studies of 

While this chapter has focussed on synthesis of polycrystalline samples, other aspects of the bismuth and thallium cuprate superconductors are discussed elsewhere. An introduction to synthesis and crystal growth is given in Chapter 5, and a review of the crystal chemistry of the two families is presented in Chapter 

The crystallographic data for these phases, including tables of calculated d-spacings and intensities for X-ray powder diffraction patterns, have been collected in Chapter 13. Characterization by electron microscopy, a particularly important technique because of the nature of the materials, is reviewed in Chapters 14 and IS. 

Bourgault, C. Martin, C. Michel, M. Hervieu, J. Provost, and B. Raveau, J. Solid State Chem. 78 326 (1989) and references therein. 

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Fig. 9.4 TPR profiles of alumina supported catalysts, oxidized 12h under flowing oxygen at 400°C (a) 1 wt.% Cu (b) 3wt.% Pt and (c) 3 wt.% Pt-1 wt.% Cu prepared by catalytic reduction. Reprinted from F. Epron, F. Gauthard, J. Barbier, Appl. Catal. A, 2002, 253-261, Copyright (2002), with permission from Elsevier.

The La2-xSrxMn04+5 (0.7 < x <1.0) phases were prepared via sol-gel route described elsewhere". Samples were annealed for 12 h at 1300 °C under flowing 5% H2-N2. The products were characterized at room temperature (RT) by laboratory X-ray powder diffraction (XRPD) with a Bruker AXS D8 Advance diffractometer. Thermogravimetric analyses (TGA) were carried out using a NETZSCH STA 449F3 thermal analyser. The sample was heated at 1 °C min in flowing O2 up to 700°C and subsequently cooled to RT. Iodometric titration has been performed on all the as-prepared samples before oxidation to estimate their initial oxygen content. 

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