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Effect of nano-sized Co3O4addition on the transport properties of YBa2Cu3O7−δ

The effect of nano-sized Co 3 O 4 (10 - 30 nm) addition on YBa 2 Cu 3 O 7−δ ( Co 3 O 4 ) x with x = 0 to 0.12 wt.% has been investigated by powder X-ray diffraction method, dc electrical resistance measurements and scanning electron microscopy. The Co 3 O 4 particle size was larger than the coherence length but smaller than the penetration depth of the YBa 2 Cu 3 O 7−δ superconductor. The onset transition temperature (T c onset) showed no significant changes for low Co 3 O 4 addition (x ≤ 0.02 wt. %) and then decreased monotonically with the increase in Co 3 O 4 content indicating a pair-breaking like mechanism in T c suppression for x = 0.03 to 0.12 wt. %. A sudden broadening of the superconducting-transition-width for x ≥ 0.11 wt. % was also observed. The transport properties were measured and related to the microstructure. Scanning electron micrographs showed homogeneous distribution of Co 3 O 4 throughout the samples and the distance between particles was smaller than 1 μm but larger than the typical Abrikosov vortex lattice constant.