Effect of Sol-Gel Synthesized BiFeO3 Nanoparticle Addition in YBa2Cu3O7–δ (Y123) Superconductor Synthesized by Standard Solid State Reaction Method

The effects of the multiforric BiFO3 nanoparticles addition on the structure and superconducting properties of YBa2Cu3O7–δ (Y123) with different concentrations were systematically investigated using X-ray diffraction (XRD), field emission scanning electron micrograph (FESEM), EDX and four point probe measurement. It was found that the added samples were predominant by Y-123 phase beside small amount of Y-211 and unreacted BiFeO3 secondary phases. Samples with less (wt.%) BFO added YBCO precursor powder preserved the orthorhombic structure similar to the pure YBCO, while samples with higher wt% addition show orthorhombic-to-tetragonal transition tendency. The samples became more porous and their grain size slightly decreased with addition of BiFeO3. The addition of nanoBiFeO3 disturbed the grain growth of Y123, thus resulting in the degradation of superconducting properties of the samples. The superconducting transition temperature (Tc onset) of samples decreased from 92 K for x=0.0 to 44 K for x=10.0 wt. %, which could be attributable to oxygen vacancy disorder.

Investigation of temperature dependence of Raman and photoluminescence analysis of YBa2Cu3O7 (YBCO) doped with SiO2 nanoparticles

We report the effect of SiO2 nanoparticles (12 nm) in YBa2Cu3O7 (YBCO) matrix. The samples YBCO and SiO2+YBCO are fabricated by a conventional solid-state reaction method, in ambiance conditions. We analyze these samples using X-ray diffraction (XRD), resonant Raman, environmental scanning electron microscopy (ESEM), and Photoluminescence (PL) as a function of temperature in the range from 77 to 837 K. The XRD confirm that the doped YBCO still displays a perovskite structure with the orthorhombic Pmmm phase. The Rietveld refinement confirms that SiO2 nanoparticles induce not only a strong effect on the oxygen?s O(5) and O(8) positions but also an elongation of the unit cell along the c-axis. The PL intensity of pure YBCO is more intense than the doped one that is mainly composed of two bands located at 2.4 eV and 1.88 eV. We simulate the PL intensity with temperature using the Bose-Einstein model with two activation energies corresponding to some specific vibration mode energies. The simulation reveals that the exchange energy between different levels in pure and doped YBCO is conducted by only two vibrations modes that are strongly linked to the oxygen and copper atoms in the YBCO matrix. We determine the evolution of Raman mode frequencies at 340 and 500 cm?1 with temperature using the Lorentzian function at q = 0 of the Balkanski model.

Experimental investigation of the Y2BaCuO5 surface free energy during peritectic solidification of YBCO

The characteristic inhomogeneous distribution of nonsuperconducting Y2BaCuO5 (211) inclusions in melt-processed YBa2Cu3O7−δ (123) grains has generally been attributed to 211 particle pushing by 123 growth fronts during peritectic solidification on the basis of reduced total surface free energy. Analysis of the morphology of the interfaces at the 211–211–123 and 211–211-liquid triple points in seeded melt-processed samples invalidates this assumption for the pure YBCO system and has implications of the mechanism of 211 particle segregation.

Neutron scattering of H.T.S.C. Materials : Zn substituted Versus Pure YBCO, Nuclear and Magnetic Structures, Spin Excitations.

ABSTRACTThe Zn substitution on Cu(2) sites in YBa2(Cu1-yZny)3O6+x materials is most probably limited to yzn ≈ 0.04. Results of neutron diffraction associated with NMR and μ+SR results reveal ; i) a lowering of TN in the pure AF region x≤0.20 due to a dilution effect of the antiferromagnetic lattice by a static non magnetic impurity, ii) the existence of a non conventionnal magnetic behavior within the intermediate region x≥0.35 characterized by an unusual temperature dependance of magnetic intensities, a reentrancy and the existence of diffuse magnetic scattering (this region is much broader in oxygen composition for Zn-doped than for pure YBCO),iii) an unusual spin dynamics in the "doped A-F phase" which corresponds to a coupling of magnetic excitations to the hole dynamics.