Conduction mechanism and impedance spectroscopy of (MnFe 2 O 4 ) x /CuTl-1223 nanoparticles-superconductor composites

Abstract

Abstract Manganese ferrite (MnFe 2 O 4 ) nanoparticles and Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3 O 10-δ (CuTl-1223) superconducting phase were prepared by sol-gel and solid-state reaction methods, respectively. MnFe 2 O 4 nanoparticles were added in CuTl-1223 matrix to get (MnFe 2 O 4 ) x /CuTl-1223 (x = 0 ∼ 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 MnFe 2 O 4 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 MnFe 2 O 4 nanoparticles at grain-boundaries of CuTl-1223 phase. In complex impedance spectroscopy (CIS), role of MnFe 2 O 4 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.