Electrical and magnetic properties of Gd(Ba2-xLax)Cu3O7+δ

摘要: We have studied the structural, electrical, and magnetic properties of normal superconducting states Gd(Ba2-xLax)Cu3O7+δ [Gd(BaLa)123] samples with 0.0 ≤x ≤0.8 prepared by standard solid-state reaction. XRD characterization shows an orthorhombic-tetragonal structural transition at x=0.2. Iodometric titration analysis oxygen content increase of La doping. The resistivity curves show that for x≤0.15, there is metallic behavior, x≥0.2, a gradual insulating transition behavior in normal state. metal-insulator superconductor-insulator transitions occur between x=0.35 x=0.4. superconducting temperature decreases content as two-step curve. normal-state fitted two and three dimensional variable range hopping (2D&3D-VRH) Coulomb gap (CG) regimes, separately. results dominant mechanism CG for x≤0.35, VRH x≥0.4. pinning energy U, derived from the thermally activated flux creep (TAFC) model Ambegaokar-Halperin (AH) theory, power-law relation U∼H -β. critical current density doping magnetic field. E-J induced electric field increases concentration. magnetization measurements indicate critical penetration fields decrease