SiO2 nanoparticles addition effect on microstructure and pinning properties in YBa2Cu3Oy

A series of YBa2Cu3Oy (YBCO, Y-123) samples with small amounts (0-1 wt%) of nanosized SiO2 particles (30 nm) are synthesized in air using a solid-state reaction route. The microstructure has been characterized by transmission and scanning electron microscopy (TEM and SEM) techniques and the magnetic field and temperature dependences of the critical current density (J(c)) was calculated from the magnetization measurements and by the standard four-probe method at various temperatures. Flux pinning force density (F-p) is calculated and possibility of the pinning mechanisms prevalent in type 11 superconductors are investigated. X-ray diffraction analysis shows that the orthorhombic structure of YBCO is maintained. Morphology examination by SEM revealed decreases of grain size with SiO2 addition. High zero resistance temperature T-co value of about 90 K was maintained in YBCO with SiO2 concentration <= 0.2 wt%. Compared to free added-sample, higher critical current densities were obtained for the YBCO sintered with low concentration SiO2 (<= 0.1 wt%) in applied magnetic field. TEM observations show the presence of columnar defects (2-3 nm in diameter) along the c-axis of YBCO and Si-rich nanophase embedded in the superconducting matrix. These defects are responsible for critical current densities improvement in the magnetic field of YBCO. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.