Doping effects on Bi-2212 high temperature superconducting thick films

Abstract

Superconducting thick films of Bi 2 Sr 2 Ca 0.95 M 0.05 Cu 2.0 O 8?d (Bi-2212) with M = K, Li, and Al were fabricated by a dip coating process. The influences of different doping elements on the lattice structure, electrical transport properties and related superconducting properties were systematically investigated. XRD analyses confirmed that all the doping ions have successfully entered into the Bi-2212 matrix, and led to a systematical change of lattice parameters. Due to the change of thermodynamic properties with doping, the phase evolution process changed during the sintering process. Thus both the content of secondary phases and the size of Bi-2212 crystals changed, which influenced the intergrain connections. The carrier concentrations of thick films were also influenced by doping, which contributed to the changes of critical temperature. It can be deduced that the hole doping with either K ? or Li ? can tune the samples into overdoping region, thus led to the increase of critical current at 77 K with the maximum critical current density of *5300 A/cm 2 .