An effective research for diffusion annealing temperature and activation energy in Au surface-layered Bi-2212 ceramic composites

Abstract

This study tries to respond two fundamental questions such as (I) what is the role of Au inclusions in the Bi-2212 polycrystalline materials prepared at the diffusion annealing temperature of 600–850 °C on the stabilization of superconductivity in small homogeneous regions and (II) what are the diffusion coefficient and corresponding activation energy of Au inclusions for the Bi-2212 superconducting system. Solution of the former question is in association with the characteristic pairing and coherence transitions extracted from the detailed dc resistivity versus temperature measurements when the latter questions are answered by the change of sample resistivity after the removal of thin-layer from the surface with the aid of the Arrhenius relation for the first time. The experimental measurement results show that the optimum diffusion annealing temperature is observed to be 800 °C where the minor phase, local structural distortions, dislocations, lattice defects and disorders in the Bi-2212 compounds degrade considerably and reach the global minimum points. Similarly, the Josephson coupled energy resides in the maximum value, and thus the superconducting grains become more and more coupled due to the increment in the percolation of intergrains. Moreover, the diffusion coefficient of Au individuals is obtained to increase regularly from 3.6186 × 10−8 to 2.79278 × 10−7 cm2 s−1 with the enhancement in the diffusion annealing temperature. At the same time, the temperature-dependent diffusion coefficient and related activation energy values of Au are computed to be about 2.601 × 10− 6 cm2 s−1 and 1.523 eV, respectively. According to the results calculated, 1.523 eV is the required minimum activation energy for the penetration of Au (heavy metal) ions into the Bi-2212 crystal structure.