Application of hot isostatic pressing in the synthesis of Hg-based superconductors

The preparation of Hg(Pb)BCCO (1201) and (1223) phases was performed by hot-isostatic-pressing (HIP) using simple oxides as precursors canned in silver tube. In the case of Hg/sub 0.8/Pb/sub 0.2/Ba/sub 2/CuO/sub 4+/spl delta// the preparation, carried out at 800/spl deg/C and 0.15 GPa for 5 hrs, yielded a single phase bulk sample. On the other hand the preparation of Hg/sub 0.8/Pb/sub 0.2/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub 8+/spl delta// at 820/spl deg/C and 0.15 GPa for 5 hrs allowed the attainment of a high volume fraction of 1223 phase. Magnetic susceptibility of 1201 phase showed an intragranular transition around 90 K; in the case of 1223 the value was /spl ap/128 K followed by a broadened intergranular transition. These results show the feasibility of 1201 phase synthesis with high purity and of 1223 phase in large amount (>80%). The possibility to obtain the samples directly in form of dense bulks (with density /spl ges/85%) stresses the importance of this technique in relation to the intrinsic low thermal stability of the superconducting phases.