New high-
Tc oxide compounds, whose superconducting transition
Tc's exceed 100K, were discovered in Bi-Sr-Ca-Cu-O (BSCCO) and Tl-Ba-Ca-Cu-O (TBCCO) systems. The stoichiometric composition of the high-
Tc phase was found to be Bi
2Sr
2Ca
2Cu
3Ox and Tl
2Ba
2Ca
2Cu
3O
x. Upper critical field
Hc2's of these compounds were evaluated for bulk sintered specimens. The
Hc2 (
T=0K) defined at the midpoint of the resistive transitions are 160T and 220T for BSCCO and TBCCO high-
Tc phases, respectively. High values of critical current density
Jc at 77K have been already attained for sputtered BSCCO and TBCCO, while the
Jc of the bulk specimens still remain less than 10
4A/cm
2 at 77K and 0T. The parameters restricted the
Jc in the bulk polycrystalline materials are considered to be (1) anisotropy in
Hc2 and
Jc, (2) weak link between grains, (3) weak pinning force, and (4) flux creep. The effect of each parameters is discussed with the experimental results of
Jc and magnetic measurements.
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