Dielectric properties of oxygen post-annealed Cu 0.5 Tl 0.5 Ba 2 Ca 3 (Cu 4−y Cd y ) O 12−δ bulk superconductor

Oxygen post-annealing experiments are carried out to optimize the oxygen contents in Cu0.5Tl0.5Ba2Ca3(Cu4−yCdy)O12−δ (y ¼0, 0.25, 0.5, and 0.75) superconductor samples and to investigate its effects on their dielectric properties {i.e. dielectric constants (e′r, e″r), absolute dielectric loss | tan δ| and ac-conductivity (sac)}. The negative capacitance (NC) is observed in all post-annealed Cu0.5Tl0.5Ba2Ca3(Cu4−yCdy)O12−δ samples. Almost all the dielectric properties are suppressed except dielectric loss (tan δ), which is increased after oxygen post-annealing. The appreciable change in the dielectric properties is the indication of oxygen intake by Cu0.5Tl0.5Ba2Ca3(Cu4−yCdy)O12−δ samples after oxygen post-annealing. The thermal agitation is higher and polarizability is lower at normal state (300 K), resulting in decrease of the dielectric constant and increase in tan δ which is vice versa at lower temperatures. The observed variation in the dielectric behavior of Cu0.5Tl0.5Ba2Ca3(Cu4−yCdy)O12−δ samples strongly depends on the working (or operating) temperature and frequency of the external applied ac-field. The dielectric behavior of the material can be regulated by the post-annealing in oxygen as a result of which the variation of oxygen content of the materials structures may take place thus changing the carrier's density. On the other hand, this post-annealing may affect the inter-grain connectivity of the materials that can influence the dielectric properties of the material. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.