TY - JOUR
T1 - Multi-step process to prepare bulk BSCCO (2223) superconductor with improved transport properties
AU - Tampieri, A.
AU - Calestani, G.
AU - Celotti, G.
AU - Masini, R.
AU - Lesca, S.
PY - 1998/9/10
Y1 - 1998/9/10
N2 - BSCCO (2223) superconducting powders were prepared by three different techniques (solid state, pyrolysis and sol-gel) and with three different stoichiometries, especially based on variations of Ca/Sr ratio and Cu concentration. Pressureless sintering was performed on cold uniaxially pressed (1 GPa) samples, avoiding the drawbacks connected to hot-pressing; different hot-forging cycles were then applied to attain higher density and orientation factor. It was found that the process phenomenology is strictly linked to the powder starting stoichiometry: when composition is very near to the theoretical (2223), effects of secondary phase extrusion are observed during hot-forging, yielding a purification and inhibition of (2212) formation accompanied by an appreciable increase of Jc respect to hot-pressed samples. When a Ca/Sr ratio is considerably > 1, recrystallisation of (2223) from the liquid takes place, with a remarkable improvement of critical current density (Jc > 104 A/cm2). In this case the non-superconducting secondary phases act as intrinsic oxygen reservoir. Finally, when composition diverges even more from (2223) (Ca/Sr ≫ 1 and Cu excess), the formation of too many precipitates of non-superconducting phases hinders the texturing process and more in general deteriorates the intergranular properties.
AB - BSCCO (2223) superconducting powders were prepared by three different techniques (solid state, pyrolysis and sol-gel) and with three different stoichiometries, especially based on variations of Ca/Sr ratio and Cu concentration. Pressureless sintering was performed on cold uniaxially pressed (1 GPa) samples, avoiding the drawbacks connected to hot-pressing; different hot-forging cycles were then applied to attain higher density and orientation factor. It was found that the process phenomenology is strictly linked to the powder starting stoichiometry: when composition is very near to the theoretical (2223), effects of secondary phase extrusion are observed during hot-forging, yielding a purification and inhibition of (2212) formation accompanied by an appreciable increase of Jc respect to hot-pressed samples. When a Ca/Sr ratio is considerably > 1, recrystallisation of (2223) from the liquid takes place, with a remarkable improvement of critical current density (Jc > 104 A/cm2). In this case the non-superconducting secondary phases act as intrinsic oxygen reservoir. Finally, when composition diverges even more from (2223) (Ca/Sr ≫ 1 and Cu excess), the formation of too many precipitates of non-superconducting phases hinders the texturing process and more in general deteriorates the intergranular properties.
KW - BSCCO (2223) superconductor
KW - Pyrolysis
KW - Sol-gel
KW - Solid state
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U2 - 10.1016/S0921-4534(98)00353-0
DO - 10.1016/S0921-4534(98)00353-0
M3 - Article
AN - SCOPUS:0032157160
SN - 0921-4534
VL - 306
SP - 21
EP - 33
JO - Physica C: Superconductivity and its Applications
JF - Physica C: Superconductivity and its Applications
IS - 1-2
ER -