SYNTHESIS AND HIGH OXYGEN-PRESSURE ANNEALING EFFECTS IN (BI,CU)-1212 CUPRATES

The origin of superconductivity in samples of (Bi0.3+.Cu0.7)Sr2-Y1-mCu 2Oz (m=0.2 and 0.3) was investigated and was found to be due to a smal l amount of Bi-2212 phase. A virtually single phase of Bi-based 1212-t ype materials was prepared with the nominal composition of (Bi0.3Cu0.7 )Sr2YCu2Oz, which was insulating after sintering in air. Following hig h oxygen pressure annealing the oxygen content z was greatly increased , and superconductivity was induced at T(c)onset=18 K, and T(c)R=0=15 K for z=7.125. The superconducting volume fraction was found to be sma ll, and the conductivity of non-metallic regions in the annealed sampl es follows the variable range hopping law, suggesting that carrier loc alization is still preponderant and more mobile holes are needed for g etting both higher T(c) and higher volume fraction in this system.