Abstract
The critical current density, Jc  has been the most important parameter used in the design and engineering of effective devices which is one of the implementation of high temperature superconductors (HTSC). In this work, an effort has been made to further improve the critical current density of YBa2Cu3O7-x (YBCO) thin films by preventing the magnetic flux line lattice against the Lorentz force by pinning it in place with the aid of nano-dimensional defects. These defects were generated by distributing nano sized CeO2 islands after YBCO layer was created on LaAlO3 substrates perpendicular to the film using pulsed laser deposition (PLD) technique. Three samples with buffer layers of CeO2 were prepared. CeO2 with 50 pulses, 100 pulses and 150 pulses, after each 1000 pulses of YBCO were prepared five layers for each of the samples. The structural characterization of YBCO/CeO2 and YBCO pristine films were carried out using x-ray diffraction (XRD) and scanning electron microscopy (SEM). Superconducting proprieties were measured using a vibrating sample magnetometer (VSM). Jc  for the pure YBCO and the YBCO/CeO2 films were calculated from magnetization (M) versus Field (H) loops using Bean’s model. Jc  for the 50 pulses of YBCO/CeO2 films was found to be increased slightly by an order of magnitude of about 40% with respect to those of YBCO films without the nano dimensional defects.
Highlights
YBa2Cu3O7−x (YBCO) film has attracted a lot of attention in electrical power applications due to its high critical transition temperature Tc (>90 K) and critical current density Jc (>1 MA cm−2) (Lei, Zhao, Xu, Wu, & Chen, 2011; Haugan, Barnes, Brunke, Manrtense & Murphy, 2003)
The (00l) peaks in the x-ray diffraction (XRD)-spectra indicate that YBCO thin films are highly c-axis oriented, which is commonly observed and corresponds to the natural growth of the material
The XRD pattern from the YBCO and YBCO/CeO2 deposited on LaAlO3 at 850°C and 300mTorr of oxygen pressure, is shown in figure 2
Summary
YBa2Cu3O7−x (YBCO) film has attracted a lot of attention in electrical power applications due to its high critical transition temperature Tc (>90 K) and critical current density Jc (>1 MA cm−2) (Lei, Zhao, Xu, Wu, & Chen, 2011; Haugan, Barnes, Brunke, Manrtense & Murphy, 2003). The critical current density is highly influenced by flux lattice motion due to thermal fluctuations and Lorentz force due to applied magnetic fields. To maintain the necessary levels of high Jc in high applied magnetic fields we need high spatial densities or naturally occurring growth defect to suppress the thermal fluctuations to stop the vortex mobility by pining them. Nanodots of CeO2 have been shown to induce additional flux pinning, this has always been due to strain in the YBCO lattice because of these inclusions. Such strain could have detrimental effect on the YBCO. Aside from the thickness dependence of Jc, there is a limitation placed on the thickness at which such films could be grown (Uzun & Avci, 2014; Zhao, Iton & Goto, 2014; Sueyoshi, Kotaki, Fujiyoshi, Mitsugi, Ikegami & Ishikawa, 2013)
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