Improvement of critical current density in YBa2Cu3O7-δ superconductor with nano TiO2 addition

The optimization of flux line pinning in superconductors is one of the most efficient ways to improve the transport properties of these materials. In this work, we have examined the effectiveness of an insulating nano particle inclusion in a type II superconductor as a pinning center with a size close to the coherence length, xi. We report on measurements of the superconducting properties of YBa2Cu3O7-delta bulk superconductors with different weight % of nano particles of TiO2 contents (x = 0-3 wt %) prepared by the modified combustion route. The microstructure of bulk YBCO added with nano particles was characterized by scanning electron microscopy. Sub-micron, randomly oriented particles of this phase were found to form around grain boundaries and within YBCO grains in bulk sintered pellets. It is observed that the critical current density is higher by a factor of 3 and the J(c)-B behavior is remarkably improved in samples with nano additions. However, the superconductor transition temperature (T-c) slightly decreases from 92K to 90.5K. The flux pinning force is enhanced by 8 times that of pure YBCO sample. Thus these nano particles are effective flux pinning centers and enhance the transport critical current density at liquid nitrogen temperature for an applied magnetic field. The experimental results suggest that the added nano-sized TiO2 particle may have high pinning efficiency at a temperature around 77 K. (C) 2015 Elsevier Ltd. All rights reserved.