Electrical conductivity of g-Bi2O3-V2O5 solid solution

The total conductivity (σ_T) in bcc γ-Bi₂O₃ doped with V₂O₅ system has been measured in the composition range between 1 and 7 mol% V₂O₅ at different temperatures. Phase transitions for different addition amounts depending on the temperature were investigated by quenching the samples. According to the XRD and DTA/TG results, this bcc type solid solution was stable up to about 720°C and the solubility limit was found at ˜7 mol% V₂O₅ in γ-phase. This system showed predominantly an oxide ionic conduction. As the V₂O₅ addition increased, the ionic conduction increased up to 5 mol% V₂O₅ at which the highest conductivity was found to be 8.318·10^-2 Ω^-1 cm^-1 at 700°C and then decreased. It has been proposed that γ-Bi₂O₃ phase contains a large number of oxide anion vacancies and incorporated vanadium cations at tetrahedral sites which affect the oxygen sublattice of the crystal structure. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of Gd addition on the activation energies of Bi-2223 superconductor

We have investigated the effect of addition of Gd in Bi_1.8Pb_0.35Sr_1.9Ca_2.1Cu₃Gd_xO_y superconductor with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5. The samples were prepared using the standard solid-state reaction method. The activation energies, irreversibility fields (H_irr), upper critical fields (H_c2) and coherence lengths at 0 K (ξ(0)) were calculated from the resistivity versus temperature (R-T) curves under DC magnetic fields up to 7 T. The superconducting transition temperature, T_c, and activation energy, U₀, were found to decrease with increase in Gd concentration and with increase in applied magnetic field. The offset transition temperature of the pure (Gd00) sample without applied magnetic field is 108 K, whereas for Gd05 sample, the offset transition temperature drops to 5 K with 7 T applied magnetic field. The activation energy of the Gd00 sample without applied magnetic field is 34,980 K, and for Gd05 sample with 7 T applied field it is 98 K. H_irr and H_c2 values also decrease with increase in Gd addition. The possible reasons for the observed degradation in microstructural and superconducting properties due to Gd addition were discussed.