Dielectric response and Cole-Cole plot analysis for (Zn_(0.91)Mn_(0.03)Co_(0.06)O)_xCu_(0.5)Tl_(0.5)Ba_2Ca_2Cu_3O_(10-δ) diluted magnetic semiconductor/superconductor composites

摘要

Adding nanoparticles (NPs) inclusions in the superconducting matrix is usually a very effective way to improve many of the high temperature superconductors (HTS) critical parameters. In this study, the influence of adding Zn_(0.91)Mn_(0.03)Co_(0.06)O NPs on the superconducting and the dielectric properties of Cu_(0.5)Tl_(0.5)Ba_2Ca_2Cu_3O_(10-δ), CuTl-1223, superconducting phase was investigated. The wet chemical Co-precipitation method was employed to prepare Zn_(0.91)Mn_(0.03)Co_(0.06)O NPs. Four samples of type (Zn_(0.91)Mn_(0.03)Co_(0.06)O)_x/CuTl-1223, with x = 0.00, 0.02, 0.06 and 0.10 wt.％, were prepared by the standard solid state reaction technique. XRD results indicated that the samples possess single phase of CuTl-1223 with tetragonal structure and that the addition of Zn_(0.91)Mn_(0.03)Co_(0.06)O did not modify the structure of the phase. SEM micrographs showed apparent suppression of voids in CuTl-1223 samples after Zn_(0.91)Mn_(0.03)Co_(0.06)O addition. Moreover, the randomly oriented plate-like morphology of the samples is reduced with NPs inclusions and transferred in to well-connected spherical grains. The electrical resistivity measurements showed that addition of Zn_(0.91)Mn_(0.03)Co_(0.06)O NPs in minor content (x = 0.02 wt. %) enhances the superconducting transition temperature (T_c) of CuTl-1223 phase to 124.5 K. Moreover, the suppression in T_c for x ＞ 0.02 wt. % was attributed to ferromagnetic nature of Zn_(0.91)Mn_(0.03)Co_(0.06)O NPs that will initiate Cooper pair breaking. The real and imaginary dielectric constants (ε' and ε"), dissipation factor (tan Δ) and ac conductivity (σ_(ac)) were investigated as a function of frequency (10~2-10~6 Hz) and NPs addition at room temperature. The results clarified that all these dielectric parameters were strongly dependent on both frequency and NPs addition and that the samples possess colossal dielectric constants with low dissipations in the low frequency regime. Cole-Cole plot of the complex permittivity was investigated for the prepared samples. With the aid of Cole-Cole plot, the static dielectric constant (ε_s), optical dielectric constant (ε_∞), distribution parameter (α), mean relaxation time (τ_o) and molecular relaxation time (τ) were estimated as function of NP content.