The effects of Ag addition on some physical properties of Y Ba 2 Cu 3 O 7−δ superconductor has been studied. The samples were produced by different routes and characterized by scanning electron microscopy, differential thermal analysis, thermogravimetric analysis, X-ray diffraction and nanoindentation. The superconducting properties were studied by dc magnetization and electrical resistivity measurements. The X-ray patterns revealed that all samples were polycrystalline and corresponded to the orthorhombic Y Ba 2 Cu 3 O 7−δ phase. However, for some samples, silver appears to be present within the grains. The superconducting properties were not significantly influenced by Ag addition. Hardness and elastic modulus were also obtained by instrumented indentation. Ag addition was found to be effective in improving the mechanical properties, probably by filling the pores in the grain boundaries. Hardness profiles indicated values between 3.1 and 3.4 GPa at deep tip penetration depths. The highest elastic modulus of 146 GPa was attained for samples prepared using Y 2 O 3 , BaCO 3 , CuO and Ag 2 O as precursors, while the lowest modulus (125 GPa) was obtained for the pure Y Ba 2 Cu 3 O 7−δ sample.

Systematic measurements of the in-plane and out-of-plane fluctuations magnetoconductivity in a melt-textured sample of YBa 2 Cu 3 O 7-δ are presented. The experiments were performed in fields ranging from 0.02 T to 5 T applied perpendicular to CuO 2 atomic (ab) planes. The measurements of the in-plane fluctuations were performed in zero applied field. The method of analysis is based on the determination of the quantity [Formula: see text], where Δσ = σ - σR is the fluctuation conductivity. In the normal phase, contributions from Gaussian regimes are clearly evidenced. These regimes are unstable regarding the application of magnetic fields perpendicular to the ab plane. Below TC, in approaching the zero resistance state, our results show a power-law behavior, that is indicative of a phase transition from paracoherent to a coherent state of the granular array.

Systematic conductivity measurements near T C in granular Ag-doped YBa 2 Cu 3 O 7−δ superconductors are presented. Silver doped YBa 2 Cu 3 O 7−δ samples were produced by different routes and characterized by X-ray diffraction, dc magnetization and electrical resistivity. The results were analyzed in terms of the temperature derivative of the resistivity and of the logarithmic temperature derivative of the conductivity, that allowed identifying power-law divergences in the conductivity. The results show that the resistive transition proceeds in two stages. In the normal phase, Gaussian and critical fluctuation conductivity regimes were identified. Close to the zero-resistance temperature, a coherence transition related to the connective nature of the granular samples was evidenced. It was not observed significant differences in critical and Gaussian fluctuations between pure and Ag-doped YBa 2 Cu 3 O 7−δ polycrystalline samples.