Unraveling the Scaling Characteristics of Flux Pinning Forces in Bi1.6Pb0.4Sr2Ca2−xNaxCu3O10+δ Superconductors

Abstract

The temperature and magnetic field dependence of the critical current density (J c) and pinning force density (F p) in Bi 1.6 Pb 0.4 Sr 2 Ca 2Àx Na x Cu 3 O 10+d (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.10) high-temperature superconductors is reported. Polycrystalline samples were prepared by a conventional solid-state reaction route. The influence of Na substitution on J c and F p at temperatures ranging between 65 K and 25 K was investigated. The collective pinning model is successfully applied to describe the magnetic field dependence of J c for all the samples investigated. Magnetic field-temperature phase diagrams were also constructed to illustrate the effects of Na substitution in different field regions. The power-law dependence of the maximum F p (F p,max) versus the irreversibility field (B irr) at different temperatures shows nearly unchanged exponent values, suggesting temperature independence of the flux pinning mechanism in the Na-substituted samples. The dominant pinning mechanism is confirmed to be dl pinning, induced by fluctuations in the mean free path of charge carriers.