Near-net-shape fabrication of continuous Ag-clad Bi-based superconductors
We have developed a near-net-shape process for Ag-clad Bi-2212 superconductors. This alternative to the powder-in-tube process offers the advantages of nearly continuous processing, minimization of processing steps, reasonable ability to control the Bi-2212/Ag ratio, and early development of favorable texture of the Bi-2212 grains. The powder is rolled into an Ag channel, a cap is applied, and the assembly is lightly rolled. To minimize distortion during heat treatment, it is especially important that the Bi-2212 powder be nearly free of volatile species such as carbon. A vacuum-calcination process was developed to control CO/sub 2/ evolution during heating. Superconducting properties are discussed.
Bi2Sr2CaCu2Ox/Ag multilayer tapes with Jc>500 000 A/cm2 at 4.2 K and 10 T by using pre-annealing and intermediate rolling process
Abstract The high transport critical current density ( J c )>500 000 A/cm 2 at 4.2 K, 10 T (critical current>700 A) is obtained in the Bi-2212/Ag multilayer tape fabricated by using the PAIR ( P re- A nnealing and I ntermediate R olling) and melt–solidification process. The combination of the improvement in geometric configuration of the tape and PAIR process make it possible to obtain the most preferable microstructure and enormous J c . Effect of processing and geometry of the tape on J c and Bi-2212 grain alignment has been studied. The enormous transport J c is attributed to highly textured grain alignment and uniformity in the tapes, which are achieved by PAIR process. After post annealing in flowing argon at 450°C for 4 h, transition temperature T c is increased from 83 K to 92 K and transport J c >25 000 A/cm 2 at 77 K is obtained. PAIR process is applicable for fabricating long Bi-2212 tapes with large transport J c for practical applications.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.