Texture improvements in the high-temperature superconducting Bi₂Sr₂Ca₁Cu₂Ox̳/Ag system via surface energy driven grain alignment

Abstract

The relation between processing, microstructure, and material property was investigated in the high-temperature superconducting Bi₂Sr₂Ca₁Cu₂Ox̳/Ag system. Experiments were based on a theoretical surface energy model proposing enhanced texture of the oxide at the Ag interface after melt-processing. Two classes of samples were processed and compared. Bi-2212 powder was deposited on a thin-foil Ag surface and was melt-processed to yield a 20 ± 10 micron-thick superconducting layer. A subset of these samples were processed with an additional Ag surface pneumatically pressed on top of the superconducting layer before heat treatment. Critical current density (...) measurements were performed in liquid helium and we obtained values ranging from 5,900-36,700 A/cm². A 3-6 fold increase in ..., for samples with the second Ag interface was observed. X-ray diffraction provided a technique for quantifying grain alignment via the Lotgering factor, and indicated samples with the upper Ag interface possess a higher degree of texturing. Our results support the interfacial energy model that a high degree of texture exists at the Ag surface, and provide clear evidence linking materials processing, superconducting grain alignment, and critical current density. Disparities observed in J for similarly processed samples were believed to be a consequence of local regions of alignment and the presence of impurities.