Preparation of oxide superconductors via a modified citrate sol-gel method

The high-Tc superconducting Y-Ba-Cu-O, Bi-Ca-Sr-Cu-O, and Tl-Ca-Ba-Cu-O materials were synthesized using a modified citrate process. Ethylenediamine was used to neutralize the metal citrate solution and facilitate the complex formation. Highly homogeneous and viscous gel without any precipitation can be obtained. In Tl-Ca-Ba-Cu-O system, the Ca-Ba-Cu-O precursor was first prepared by sol-gel method, then mixed with thallium oxide for final sintering. The complex formation was monitored by UV/VIS and IR spectrophotometry. The thermal decomposition of gels and the formation of superconducting phases had been studied using DTA, TGA, XRD, and SEM. This process is highly reproducible and leads to powders with excellent homogeneity and small particle size for easy sinterability