AC-field frequency response of Cu _0.5Tl _0.5Ba ₂(Ca _2-q Mg _q )Cu ₃O _10-δ bulk superconductor

The dielectric properties of Cu _0.5Tl _0.5Ba ₂Ca _2-q Mg _q Cu ₃O _10-δ (q=0, 0.5, 1.0 1.5) superconductor samples were studied at two temperatures of 80 and 290 K by capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 KHz to 10 MHz. We have presented the measurements of the dielectric constants (ε′ and εâ€), dielectric loss factor (tan∈δ) and ac-conductivity (σ _ac) as a function of frequency and temperature. A negative capacitance (NC) experience has been observed, which is most likely due to different contact electrodes and superconductor samples' Fermi levels. Since metals have their Fermi levels higher than ceramics, there is a flow of the carriers from the ceramic samples towards the metal electrodes. The dielectric polarization phenomenon is observed, which is due to dislodgment of mobile charges from their equilibrium position relative to fixed charges of the reservoir layer. The improved inter plane coupling promoted by Mg substitution at Ca site would change the dielectric response of Cu _0.5Tl _0.5Ba ₂Ca _2-q Mg _q Cu ₃O _10-δ superconductors. To observe such effects in Mg doped Cu _0.5Tl _0.5Ba ₂Ca _2-q Mg _q Cu ₃O _10-δ superconductors, di- electric measurements were carried out both at room temperature (290 K) and in the superconducting state closer to the boiling point of liquid nitrogen (80 K). The excess conductivity arising due to superconducting state of material has been determined, and its role in the mechanism of superconductivity is suggested. The negative dielectric constant (ε′) and dielectric loss factor (tan∈δ) show strong dispersion at low frequencies. The lower thermal agitation at 80 K may enhance the polarizability and hence the dielectric constants (ε′ and εâ€).