Because of the mixed metal valance state of thallium in a Tl-based superconductor, a nearly single ‘‘1223’’ phase can be readily prepared by a modified Pechini method (US Patent 3 330 697). Tl2O3 and other metal nitrates are dissolved in an aqueous solution plus a certain amount of oxalic acid for chelating the metal cations. The desired phase shows zero resistance at 114 K and the phase purity is identified by x-ray diffraction. Characteristics of superconductivity also are evidenced by the Meissner effect. The preparation technique is considered valuable to purify multiphase superconductors for mass production.

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Differential thermal analysis (DTA), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM) were carried out to investigate the origin of the partial melting which is closely related to the formation of the 110 K superconducting phase in the Bi-Pb-Sr-Ca-Cu-0 system. The occurrence of a liquid phase in the presence of the Bi2Sr2Ca-Cu20,, Ca2Pb04, and CuO phases was demonstrated. Large grain growth and promotion of the 2223 phase formation resulting from the reactive liquid-phase-aided sintering were also observed. [

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