Frequency and temperature dependent dielectric constant of (Ag)x/CuTl-1223 nanoparticles-superconductor composites

Abstract

Polycrystalline superconducting CuTl-1223 samples were prepared by solid state reaction method. Synthesis of silver nanoparticles was done using the well known Sol-gel method. Silver nanoparticles with different concentrations i.e. x = 1, 2, 3 and 4 wt % were added to CuTl-1223 host superconductor to get (Ag)x/CuTl-1223 composites. XRD of composites shows that the added nanoparticles did not affect the crystal symmetry of CuTl-1223 phase which indicates that the nanoparticles were settled at the grain boundaries. The capacitance and conductance of the samples were measured at various frequencies (40 Hz- 100 MHz) and temperatures (77–253 K). The dielectric parameters such as real part (ԑr/) and imaginary part (ԑr//) of dielectric constant, dielectric loss (tanδ) and ac-conductivity (σac) were calculated from the measured capacitance and conductance. The parameters ԑr/, ԑr//and tanδ were reduced while σac was increased with the increasing frequency and reached saturation at higher frequencies. On the other hand ԑr/, ԑr//and tanδ were found to increase and σac suppressed with the increasing contents of Ag nanoparticles except for x = 2 wt%. The increase in the dielectric constant with the increasing x-contents may arise due to piling up of the free carriers (contributed by the conducting Ag nanoparticles) at the grain boundaries that play a key role in the space charge polarization.