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Abstract  

Thermal decomposition of metal-organic precursors for the mixed oxide BaBiO3 was studied using TG and EGA. Precursors produced by polyesterification of bifunctional acids with ethylene glycol (Pechini process) decomposed about 100°C higher than those without the diol. BaCO3 was identified by IR and XRD as a reaction intermediate. EGA proved that the amount of BaCO3 was below 10% of the total barium, and that the barium exists mainly as a nitro-compound up to 650°C. Phase-pure BaBiO3 with a moderately high surface area (1.4 m2/g) could be synthesised from a citrate precursor by the Pechini process at around 850°C.

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Abstract  

The effects of barium substitution for Bi or Sr sites on the growth of superconducting phases have been studied. The sol spray process has been used to synthesis the Bi-Sr-Ca-Cu-O (BSCCO) and Ba-BSCCO homogeneous ceramic powders. Thermogravimetric (TG), differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques were employed to characterize the synthesized materials. The electrical resistance was measured by classical d.c. fourprobe technique. It has been observed that sol spray process has affected the physico-chemical properties of the materials and also avoid the use of chelating agent as in the case of sol gel process. In addition to the Bi2Sr2CaCu2O8 (2212) phase Ba doped specimens also contained Bi2Sr2Ca2Cu3O10 (2223), BaBiO3, BaCuO2 and CuO phases. The results revealed that the specific effect of barium-doping on either sites (Bi or Sr) seems to avoid the formation of higher volume fraction of the low T c phase and promoting the formation of BiBaO3, BaCuO2 and CuO along with formation of a high T c 2223 phase. The substitution of Ba on either sites (Bi or Sr) lower the sintering temperature for the formation of high T c (small volume fraction) however, the Ba doped specimens also contained non-superconducting phases.

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