Abstract
The effect of nano-size Zn 0.95Mn 0.05O and ZnO (30 nm) addition on the microstructure and the normal state transport properties of polycrystalline YBa 2Cu 3O y (YBCO) was systematically studied. Samples were synthesized in air using a standard solid state reaction technique by adding nano-sized particles up to 10 wt.%. When Zn 0.95Mn 0.05O and ZnO are added to the YBCO the orthorhombic structure maintained even at the highest concentration. TEM and EDS analyses show the presence of inhomeginities embedded in the superconducting matrix. To interpret the normal state properties of the samples, the percolation theory based on localized states is applied. A cross-over between variable-range hopping and Coulomb gap mechanisms is observed as a result of increasing the nano-particles concentration. The ZnO addition modifies the electrical behavior of samples from metallic to insulating with a much lower concentration comparatively to Zn 0.95Mn 0.05O addition. The calculated values of the localization length, d, are greater in the case of Zn 0.95Mn 0.05O addition. This result can be interpreted by the internal structure defects.
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