Magneto-conductivity fluctuation in YBCO prepared by sintering of ball-milled precursor powder

We compare the electrical magneto-conductivity fluctuation between YBa2Cu3Oy (Y-123) and YBa2Cu3Oy embedded by an Y-deficient Y-123 nano-phase, generated by planetary ball-milling. Both samples were synthesized by solid state reaction with two stages of sintering at 950 degrees C and separated by energetic milling (milled sample) and hand grinding (unmilled sample). SEM analysis of the milled samples shows the appearance of spherical shaped nano-entities of Y-deficient Y-123 embedded in the Y-123 matrix. The magneto-conductivity data are analysed in terms of the temperature derivative of the resistivity and the logarithmic temperature derivative of the conductivity. The results show the occurrence of two-stage transitions: intragranular and intergranular, as well as a pairing transition splitting in the milled sample related to the presence of the Y-deficient nanoparticles. In the normal state, we identify a contribution of the Gaussian regimes for both samples. In the presence of a high magnetic field, the critical exponent near T-co of the milled material is higher than the one of the unmilled, indicating that the nanoparticles strengthen the effects of the order-parameter phase of individual grains of the Y-123 strongly disordered. This result fits well into a description based on a dirty limit of the general vortex-glass theory. In the paracoherent state, a crossover occurs and a small temperature range appears where the fluctuation conductivity may be governed by others mechanisms related to vortices dynamics. This temperature range is smaller in the milled sample. (C) 2015 Elsevier B.V. All rights reserved.