BI-BASED 2223 SUPERCONDUCTING POLYCRYSTALLINE MATERIALS PREPARED BY EITHER A SOLID-STATE ROUTE OR A GLASSY MATRIX PRECURSOR METHOD - CHEMICAL-ANALYSIS AS WELL AS ELECTRICAL AND THERMAL TRANSPORT-PROPERTIES

Two routes have been followed in order to prepare Bi1.7Pb0.3Sr2Ca2Cu3O(y) superconducting materials. Bi1.7Pb0.3CuO4 is always used as one of the starting basic materials. The first route involves a new experimental procedure based on the solid state synthesis of separate intermediate phases, mixed together in a two (Bi1.7Pb0.3CuO4 + 2SrCaCuO3), three (Bi1.7Pb0.3CuO4+2SrCuO2+2CaCO3) or four (Bi1.7Pb0.3CuO4+(1/12)Sr8Ca6Cu24O41 + (3/2)CaCO3 + (4/3)SrCO3) powder process. Electric resistivity versus temperature measurements are presented. Even though the T(c)(0) of each sample is above 100 K, X-ray diffraction shows that the main phase is the 2212 phase in each case. Relatively pure 2223 materials have, however, successfully been produced by the second method, which starts from a glassy intermediate phase and involves a so-called 'matrix' method. The glass precursor phase is composed of one (Bi1.7Pb0.3CuO4), two (Bi1.7Pb0.3CuO4 + 2CaCO3), and three (Bi1.7Pb0.3CuO4 + (3/2)CaCO3 + (4/3)SrCO3) components as for the solid state routes. The role of both the added alkaline earth crystalline compounds and the glass matrix precursors in this second method turns out to be very important. We propose a schematic structural model in order to explain the selectivity of the starting materials. SrCaCuO3 is found to be a good precursor of the 2212 phase, while SrCuO2 gives rise to the 2223 phase. It seems that the presence of CaCO3 in the glassy intermediate phase, thus acting as a cation reservoir, is very useful for the production of the 2223 phase. Electric resistivity, thermal conductivity and thermopower versus temperature measurements are also presented and discussed in terms of intergrowths and variations of cationic compositions in the Bi-based layers.