AC Conduction Mechanism in (Cu)x/(CuTl)-1223 Nanoparticles–Superconductor Composites

Abstract

Copper (Cu) nanoparticles (NPs) were prepared by sol–gel process, and superconducting (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ {(CuTl)-1223} phase was synthesized by conventional solid-state reaction. The desired (Cu)x/(CuTl)-1223, x = 0–4.0 wt% composites, were obtained by adding Cu NPs in superconducting (CuTl)-1223 phase. These composites were characterized by X-ray diffraction, DC-resistivity versus temperature (R–T) and AC conduction measurements. The tetragonal crystal structure with P4/mmm space group of the host superconducting (CuTl)-1223 phase remained dominant after the addition of Cu NPs. The zero-resistivity critical temperature Tc(0) (K) was increased, and normal state resistivity was decreased after addition of Cu NPs in CuTl-1223 phase. The frequency- and temperature-dependent AC conduction properties of (Cu)x/(CuTl)-1223 composites were explored via dielectric, impedance and electric modulus measurements. The dielectric constant (ɛr/, ɛr//) and loss tangent (tanδ) were suppressed, while AC conductivity (σac) was improved with the addition of Cu NPs in (CuTl)-1223 phase. Comparatively, the capacitance associated with grain boundaries regions was found to be greater than the capacitance associated with grain regions. The capacitive behavior of the grain boundaries was decreased, while that of the grains was increased with increasing operating temperature for all these composite samples. The shifting of peaks in imaginary part of the electric modulus (M//) versus frequency (f) spectra toward lower frequency regime with increasing Cu NPs contents in superconducting (CuTl)-1223 phase is witnessed for the existence of non-Debye relaxation in the material.