J. Kase

ANISOTROPY OF CRITICAL CURRENT DENSITY IN TEXTURED BI2SR2CA1CU2OX TAPES

Anisotropy in Jc with respect to field direction for a textured Bi2Sr2Ca1Cu2Ox tape was measured at various temperatures and magnetic fields. Anisotropy at 4.2 K was small enough for practical applications in fields up to 25 T. However, the anisotropy increases rapidly with increasing temperature. Angular dependence of Jc shows a history effect, which is characteristic of ceramic superconductors.

Enhancement of flux pinning in Bi2Sr2CaCu2O8 by 180 MeV Cu11+ irradiation

180 MeV Cu11+ irradiation was done on the c‐axis grain oriented Bi2Sr2CaCu2O8 tapes. Irradiation enhanced hysteresis in dc magnetization curves, especially in high magnetic fields. The irreversibility line can be moved to higher field by irradiation. Transport Jc is also enhanced by the irradiation of the small fluences. The irradiation produced large (∼100 nm) and small (∼5 nm) defects. They are effective for flux pinning in Bi2Sr2CaCu2O8.

Oxygen nonstoichiometry and phase instability of Bi2Sr2CaCu2O8+δ

Abstract Oxygen nonstoichiometry, δ , of Bi 2 Sr 2 CaCu 2 O 8+δ was determined by thermogravimetric measurement as functions of temperature and partial pressure of oxygen (PO 2 ). Dependencies of thermodynamic quantities, lattice constant and critical temperature on δ show anomalous behaviors at same oxygen content of δ =0.235. A quite sluggish and a large amount of weight increase observed at about 600°C under PO 2 =1 atm was found to correspond to the decomposition of Bi 2 Sr 2 CaCu 2 O 8+δ phase to BiSrCaO, Bi 2 Sr 2 CuO y and CuO. This suggests that the Bi 2 Sr 2 CaCu 2 O 8+δ phase is unstable at low temperature under high PO 2 .

BiSrCaCuO/Ag superconducting composite tapes

Bi2Sr2Ca1Cu2Ox/Ag composite tapes were prepared by the combined process of doctor blade casting and crystal growth from the partially molten state. A highly textured microstructure was obtained for oxide layer thicknesses of 15 mu m or less by solidifying from 890 degrees C The textured tapes have excellent transport Jc values greater than 105 A/cm2 at 4.2 K in magnetic fields above 25 T. The results indicate that textured Bi-based tapes are promising candidates for high field superconducting magnets.

Dependence of critical temperature and critical current of oriented Bi2Sr2CaCu2O8+ delta thick films on the oxygen content

Thermogravimetric measurement of Bi2Sr2CaCu2O8+ delta was carried out as functions of temperature and partial pressure of oxygen (PO2). Dependencies of thermodynamic quantities, lattice constant and critical temperature (Tc) on oxygen nonstoichiometry, delta , show anomalous behaviors at the same delta of 0.235. Furthermore, Bi2Sr2CaCu2O8+ delta phase is found to decompose to Bi-Sr-Ca-O, Bi2Sr2CuOy and other phases at low temperature under high PO2. Effects of oxygen nonstoichiometry and the phase decomposition on critical current density (Jc) of Bi-2212/Ag melt-solidified thick films were also studied.

Critical current density and flux pinning in textured Bi2Sr2Ca1Cu2O8 tapes

Abstract Pinning force density Fp(=Jc×B) was measured for the c-axis oriented Bi2Sr2CaCu2O8 tape conductors at various magnetic fields and temperatures. Fp appeared to obey a scaling law F p =[ B ∗ ( T )] m f( B B ∗ , where B★ is a irreversibility field above which Jc is zero. The exponent m is different between c//B and c⊥B, which suggests the difference of pinning mechanism between two field directions.

Preparation and critical current densities of highly textured 2212 BiSrCaCu oxide layers on silver

Abstract Doctor blade processed green tapes and screen printable pastes on silver foil, both prepared with Bi 2 Sr 2 Ca 1 Cu 2 O x powder, were subjected to melt-texturing using melting and crystallization temperatures derived from DTA measurements. Highly textured layers were formed by slow cooling from the melting temperature to the crystallization temperature and quenching after a holding period. Quenching increased T c to 90 K. The critical current density was measured as a function of temperature and magnetic field. At 4.2 K and 77 K and 0 Tesla, critical current densities as high as 1.3 × 10 5 A/cm 2 and 1.04 × 10 4 A/cm 2 were observed, respectively. At 4.2 K and 10 Tesla a critical current density of up to 5 × 10 4 A/cm 2 was obtained, even with B ⊥ tape

Processing and Properties of BiSrCaCuO Superconducting Tapes

Highly textured Bi2Sr2CaCu2Ox tapes were prepared by applying partial melting and slow cooling process for BiSrCaCuO/Ag composite prepared by doctor blade process and for Ag-sheathed BiSrCaCuO composite prepared by powder-in-tube method. Jc at 77K was greater than 104 A/cm2 in zero magnetic field, however, it is very sensitive to an applied magnetic field and shows a large anisotropy with resepct to field direction. These sensitivity and anisotropy are significantly reduced at lower temperatures. Jc’s at 4.2K reach practical level (~105 A/cm2) even in high magnetic fields above 20T and shows a small anisotropy factor (~1.5), which should not limit practical application.

Fabrication and Properties of Superconducting Ba-Y-Cu-O and Bi-Ca-Sr-Cu-O Tapes

Ba2YCu3Oy green tapes were fabricated by a doctor blade method and sintered at temperatures ranging from 910 to 1010C to examine the effect of sintering temperature on their properties. The tape sintered at 930 C showed the largest critical current density (Jc) of 1500 A/cm2 at 77 K. It was concluded that the Jc of our tapes are determined by the compromise of porosity, portion of superconducting phase and the loss of contact at the grain boundary.