Conduction mechanism and impedance spectroscopy of (MnFe2O4)x/CuTl-1223 nanoparticles-superconductor composites

Manganese ferrite (MnFe2O4) nanoparticles and Cu0.5Tl0.5Ba2Ca2Cu3O10-delta (CuTl-1223) superconducting phase were prepared by sol-gel and solid-state reaction methods, respectively. MnFe2O4 nanoparticles were added in CuTl-1223 matrix to get (MnFe2O4)(x)/CuTl-1223 (x = 0 similar to 2.0 wt.%) nanoparticles superconductor composites. Different experimental techniques like XRD, SEM, R-T measurements and Impedance spectroscopy were used to characterize these composites. It was observed that crystal structure of host CuTl-1223 phase remained unaltered after addition of MnFe2O4 nanoparticles, which indicated about the occupancy of these nanoparticles at grain-boundaries. Over all decreasing trend in superconducting properties may be attributed to spin-charge reflection and trapping of charge carriers across these magnetic MnFe2O4 nanoparticles at grain-boundaries of CuTl-1223 phase. In complex impedance spectroscopy (CIS), role of MnFe2O4 nanoparticles at the grain-boundaries of host CuTl-1223 phase was also investigated. The decrease in impedance (Z) with increasing temperature witnessed the occurring of thermally activated processes in the system. Higher value of activation energy at grain boundaries showed that grain-boundaries are more resistive than grains due to non-stoichiometric distribution of oxygen and dangling bonds at grain-boundaries. The impedance master curves indicated that the distribution of relaxation time (dynamic process) is nearly temperature independent. The decrease in ac-conductivity with increasing content of these nanoparticles indicated the enhancement of space charges at grain-boundaries. (C) 2017 Elsevier B.V. All rights reserved.