Determination of optimum diffusion annealing temperature for Au surface-layered Bi-2212 ceramics and dependence of transition temperatures on disorders

This study aims not only to declare experimentally the effect of diffusion annealing temperature (600 degrees C-850 degrees C) on the crystal structure, electrical and superconducting properties of Au surface-layered Bi-2212 ceramics by dc resistivity and powder X-ray diffraction measurements, but also to advance in-depth understanding of empirical relationship between the disorders and transition temperatures. It is found that the diffusion annealing temperature of 800 degrees C is found to be optimum for the improvement of crystal structure due to the retrogression of disorders and local structural-distortions in the layers, increasing metastability, sigma-gap anisotropy and softening of Ag and B1g phonons. Accordingly, the Au nanoparticles transit from inherently over-doped nature of the compound to optimally-doped state. Additionally, the empirical relations between critical temperatures and Delta rho parameters (related to disorders) show that it is possible to achieve maximum onset and offset critical temperature values of 90.467 K and 90.359 K for the Bi-2212 ceramics. (C) 2016 Elsevier B.V. All rights reserved.