PB-BASED CUPRATE SUPERCONDUCTOR WITH THE 1234-STRUCTURE SYNTHESIZED USING A HIGH-PRESSURE TECHNIQUE

We have successfully synthesized nearly single-phase Pb-1234 in oxidiz ing atmosphere using a high-pressure technique. Samples with nominal c ompositions of Pb0.5Sr2.8Ca2.7Cu4.0Ogamma (10.6 less than or equal to gamma less than or equal to 11.4) were prepared at 1000 degrees C for 4 h under 6 GPa. Nearly single-phase samples can be obtained at 10.8 l ess than or equal to gamma less than or equal to 11.0, and all of them show superconductivity. It has a tetragonal unit cell and lattice par ameters of a congruent to 3.83 Angstrom and c congruent to 18.4 Angstr om. No drastic change of the structure is observed with Varying the no minal oxygen content. (Pb0.5Sr0.3Cu0.2)Sr-2.0(Ca2.8Sr0.2)Cu4.0O9.0+del ta is postulated for the tentative composi tion of the Pb-1234 phase f rom SEM-EDX analysis. The maximum T-c for as-prepared Pb-1234 sample i s 107 K which is almost independent of the nominal oxygen content. It decreases slightly by annealing in Ar, suggesting that the as-prepared Pb-1234 phase is in slightly under-doped or nearly optimally doped st ate. (C) 1998 Elsevier Science B.V.