Enhancement in the transport critical current density Jc in YBa2Cu3O7−δ added with an insulating nano crystalline YBa2HfO5.5 perovskite

Abstract

When a magnetic field is applied to type II superconductors, such as YBa2Cu307−δ (YBCO), the flux quanta penetrate the material as a regular array of vortices. However when transport currents are applied, they act to move these vortices, thus lowers the critical current density (Jc) as well as destroying superconductivity. The development of microstructures made of YBCO materials has enabled engineers to increase the critical current density, within Type II materials by introducing flux pinning centres into the material. The microstructure and flux pinning properties of YBa2Cu3O7−δ system with varying levels (0-5 wt. %) of a nano perovskite ceramic insulator; YBa2HfO5.5 addition was studied in detail. Orthorhombic YBa2Cu3O7−δ powder was prepared through conventional solid state route and a modified combustion method was used for synthesizing nanocrystalline YBa2HfO5.5. The structure and microstructure of the samples examined by X-ray diffraction and scanning electron microscopy showed that YBa2HfO5.5 and YBCO remained unreacted even at higher processing temperature without deteriorating the superconducting properties. The scanning electron microscope image shows that YBa2HfO5.5 forms an electrical-network between grains. These observations suggest that the YBa2HfO5.5 addition to the Y-123-compounds improve the electrical connection between superconducting grains and substantial improvements in the relative electrical transport properties of the composites. The variation of sintering temperature, density, critical transition temperature (Tc) and magnetic field dependence of critical current density (Jc) of YBa2Cu3O7−δ having different proportions of YBa2HfO5.5 in the matrix were also studied in detail. It is found that the addition of these elements considerably enhances the flux pinning strength of the system, and there is also an increase of critical temperature (Tc) and critical current density (Jc) up to an optimum value of 8.76 × 104 A/cm2 for a concentration of 2 wt % addition of nano YBa2HfO5.5. The enhancement of the critical current density in the YBa2Cu3O7−δ - YBa2HfO5.5 samples is attributed to the sustained formation of the insulating and non-reacting YBa2HfO5.5 phase acting as pinning center. The addition of YBa2HfO5.5 in YBa2Cu3O7−δ bulk superconductor also enhances the pinning force density from 3 ×106 N/m3 to 69.6 × 106N/m3 at 77 K.