Dielectric properties of Cu0.5Tl0.5Ba2Ca3Cu4O12-δ bulk superconductor

The dielectric properties of Cu0.5Tl0.5Ba2Ca3Cu4O12-δ superconductor samples were studied at 79 and 290 K by means of capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 kHz to 10 MHz. A negative capacitance (NC) phenomenon has been observed, which is most likely arising due to higher Fermi level of ceramic superconductor samples than metal electrodes. Also the NC may be due to the space charge located at the multiple insulator-superconductor interfaces (grain boundaries) in the materials. The negative dielectric constant (ε') and loss factor (tan δ) show strong dispersion at low frequencies. The lower thermal agitation at 79 K may enhance the polarizability and hence the dielectric constants (ε' and ε'').