Studies of two-powders mixtures in Bi(Pb)-Sr(Ba)-Ca-Cu- oxide/nitrate system obtained by freeze drying used for synthesis of 2223 superconducting ceramic

Nitrate freeze dried raw powders Bi:Pb:Sr:Ba:Ca:Cu 1.8:0.4:1.8:0.2:2.2:3.0('2223-nitrate'). Bi:Pb:Sr:Ba:Ca:Cu 1.8:0.4:1.8:0.2:1.2:2.0 ('2212-nitrate') and Ca:Cu = 1:1 ('11-nitrate') have been decomposed at 840 deg. C for 30 min. to obtain '2223-oxide', '2212-oxide' and '11-oxide' powders. From the above powders the following mixtures (mechanically mixed) were prepared: '2212-oxide' + '11-nitrate', '2212-nitrate' + '11-oxide' and '2212-nitrate' + '11-nitrate' and thermally decomposed in the same conditions. The decomposed powders were investigated by XRD analysis. From the indicated decomposed mixtures, '2223-oxide' powder and mixture '2212-oxide' + '11-oxide' superconducting pellets with composition 2223 were sintered. Electrical resistance R(T) measurements on pellets have been performed. The obtained data have shown different phase compositions in the decomposed samples indicating different phase formation reactions. Because of this fact superconducting parameters in sintered pellets are changing. The optimum precursor powder considering R(T) results for the synthesis of 2223 phase is the decomposed sample '2212-nitrate + 11-nitrate', although the best level of mixing is in the '2223-oxide' powder. The most unfavorable mixture for 2212 and 2223-phase formation is the decomposed sample '2212-nitrate + 11-oxide' due to the lack of (Sr,Ca)CuO2 phase. (authors)