Synthesis and characterization of high-Tc superconductors in the Ti-Ca-Ba-Cu-O system--

This paper reports an effort to synthesize the high-Tc superconducting phase in the thallium system two nominal compositions, TlxCa2Ba2Cu3O10 and Tl1Ca3Ba1Cu3O8.5, have been investigated for superconductivity as a function of the sintering temperature, time, atmosphere, and quench rate. Samples have been characterized by electrical resistivity measurements, X-ray diffraction, and scanning electron microscopy. Samples of starting composition Tl2Ca2Ba2O10 fired in air at 860-900 degrees C and rapidly quenched showed Tc (R = O) of 96-107 K. In contrast, specimens of starting composition Tl1Ca3Ba1O8.5 when baked at 900 degrees C and slow cooled in oxygen were superconducting at approx-gt 116 K and consisted of Tl2Ca2Ba2Cu3O10+x as the dominant phase. The authors results also show that, in contrast to the case of YBa2Cu3O7-x, doping with a small concentration of fluorine sharpens the resistive transition and produces large Tc increase in thallium-based superconductors