Flux-pinning properties of nanocrystalline HfO2 added YBa2Cu3O7 δ superconductor

The effect of addition of different weight percentages of nanocrystalline HfO2, synthesized through a modified combustion method in bulk coarse-grained orthorhombic YBa2Cu3O7- powder was studied. The structure and microstructure of the samples examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed the formation of a secondary phase YBa2HfO5.5 in the superconductor without deteriorating the superconducting properties. The variation of sintering temperature, density, critical transition temperature (T-c), magnetic field dependence of critical current density (J(c)), and flux-pinning force (F-p) of YBa2Cu3O7- having different proportions of YBa2HfO5.5 formed in the matrix were studied in detail. The samples showed a transition temperature (T-c) of approximate to 92K and the self-field critical current density (J(c)) increases significantly up to an optimum value of 5.42x10(4)Acm(-2) for 2wt% addition of nano HfO2. The enhancement of the critical current density in the YBa2Cu3O7--HfO2 samples is attributed to the presence of the nonreacting YBa2HfO5.5 phase, formed due to the addition of HfO2 as artificial pinning center. The formation of YBa2HfO5.5 in YBa2Cu3O7- bulk superconductor also enhances the pinning force density from 3x10(6) to 30.4x10(6)Nm(-3) at 77K.