INHOMOGENEITY INDUCED CONDUCTIVITY FLUCTUATION IN YBa2Cu3O7-δ/BaTiO3–CoFe2O4 COMPOSITE

Abstract

Polycrystalline (1-x) YBa 2 Cu 3 O 7-y + x BaTiO 3– CoFe 2 O 4(x = 0.0, 0.2, 0.4, 0.6 wt. %) superconductors were prepared by solid state route. XRD analysis reveals no significant change in "b" parameter and increase in "a" and "c" parameters. SEM micrographs show no change in grain size of the samples. With the increase of BaTiO 3– CoFe 2 O 4 (BTO–CFO) addition it has been analyzed that the superconducting transition temperatures (Tc) determined from standard four-probe method was decreased and dropped sharply with higher wt.% addition. Excess conductivity fluctuation analysis using Aslamazov–Larkin model fitting reveals transition of two dominant regions (2D and 3D) above Tc. The decrease in 2D–3D crossover temperature T LD (Lawerence–Doniach temperature) in the mean field region has been observed as a consequent dominance of 3D region to increase in wt.% in the composite. The increasing value of ρwl and ρ0 and the decreasing trend in the value of zero-resistance critical temperature (Tc0) indicates that the connectivity between grains decreases gradually with the addition of magneto–electric composite BTO–CFO.