Dielectric Response of (M)z/CuTl-1223 (M=Co, Cr) Nanoparticle-Superconductor Composites

Abstract For a comparative study of dielectric response of (M)z/CuTl-1223; (M = Co or Cr) nanoparticle/superconductor composites, the nanoparticles (NPs) were separately synthesized by sol gel method and then their composites with CuTl-1223 superconducting phase were prepared by solid state reaction method. Various samples with appropriate ratio of the NPs i.e. z = 0, 0.5, 1, 1.5 wt. % were prepared. From XRD, no change was observed in the crystal structure of the host material which indicates that the NPs are settled down at the inter grain sites. Addition of Co and Cr NPs suppresses the critical temperature (Tc) of the superconductor. This suppression in Tc may be attributed to the ferromagnetic nature of Co NPs and antiferromagnetic nature of Cr NPs. A comparative study of frequency dependent dielectric response has been carried out at various operational temperatures ranging from 78 K to 288 K. The maximum values of dielectric constant (er/, er//, and tanδ) were observed at lower frequencies while at high frequencies they became saturated whereas the ac conductivity σac linearly increases up to 5 × 106 Hz and has a sharp increase beyond. er/ was less suppressed while er// and tanδ were enhanced more in case of Cr NPs than Co NPs which may be due to less magnetization of Cr NPs. AC conductivity was maximum for highest concentration of Co NPs while it suppressed with the enhanced contents of Cr NPs. This behaviour may be attributed to high surface effects of Cr NPs that enhances the barrier for charge mobility at grain boundaries in (Cr)z/CuTl-1223 composite.