Effect of MgO Nano-oxide Additions on the Superconductivity and Dielectric Properties of Cu_0.25Tl_0.75Ba₂Ca₃Cu₄O_12−δ Superconducting Phase

Abstract

The effect of MgO nano-oxide on both superconducting and dielectric properties of polycrystalline (Cu_0.25Tl_0.75)-1234 was studied. The MgO-content varied from x=0.0 up to 1.0 wt% of the sample’s total mass. The volume fraction of the prepared samples (x=0.0, 0.2, 0.6 and 1.0 wt%) was estimated from the room-temperature X-ray powder diffraction patterns. The superconducting transition temperature T _c, calculated from resistivity data, increased from 122 to 136 K as x increased from 0.0 to 0.8 wt% and then it decreased to 117 K for x=1.0 wt%. Also, the dielectric properties of all samples were measured in the frequency range from 100 Hz to 4 MHz at different temperatures from 113 to 300 K. The real part of dielectric constant ε′ was strongly dependent on both temperature and frequency for all x values. The imaginary part of dielectric constant ε″ and loss factor tan δ showed dispersion which shift toward lower frequencies with decreasing temperature. The ac conductivity σ _ac was derived from the admittance and sample dimensions in the same frequency range. It followed the power law σ _ac(ω)∼ω ^−γ with γ≈0.8.