Mary Ann Sebastian

Optimizing Flux Pinning of YBCO Superconductor With

Addition of nanophase defects to YBa₂Cu₃O₇ superconductor thin films enhances flux pinning, resulting in an increase in transport current densities (<i>J</i>_ct). While previous studies focused on single-phase additions, the addition of several phases simultaneously has shown strong improvements by combining different flux pinning mechanisms. This paper further explores the effect of mixed phase nanoparticle pinning, with the addition of insulating, nonreactive phases of BaSnO₃ and Y₂O₃. Processing parameters vary the BaSnO₃ concentration of 3, 5, and 10 vol. %, while maintaining Y₂O₃ constant at 3 vol.%. Pulsed laser deposition produces films on LaAlO₃ and SrTiO₃ substrates at deposition temperatures of 750-815°C. Current density is measured for fields ranging from <i>H</i> = 0 to 9 T with <i>H</i> // c, and temperatures from 5 to 77 K, providing a detailed picture of pinning effects. Optimized results of flux pinning, magnetic current densities <i>J</i>_cm (<i>H, T</i>), critical transition temperatures (<i>T</i>_c), lattice parameters, and microstructures are presented.

\hbox{BaSnO}_{3} + \hbox{Y}_{2}\hbox{O}_{3}

Vortex pinning by insertion of non-superconducting defects like BZO or BSO nanorods into the YBCO matrix is an effective means to enhance pinning since they self-assemble into columnar structures that provide strong pinning along the length of the flux-line. However, only limited control of their geometry is possible by current growth methods. To meet the requirements of applications that operate in magnetic fields of varying intensity or orientation, this work studies strain-mediated self-assembly of 3D pinning landscape through theoretical modeling as well as experimental exploration to achieve controllable growth BZO or BSO nanostructures in YBCO matrix films. The microstructure of BZO- and BSO-doped YBCO thin films was studied using transmission electron microscopy and the findings indicate that it is possible to produce a controllable defect landscape and improved critical current density with respect to different orientation of the magnetic field by manipulation of the strain relationships using vicinal substrates.

Dual Mixed Phase Additions

An elastic strain model was applied to evaluate the rigidity of the c-axis aligned one-dimensional artificial pinning centers (1D-APCs) in YBa2Cu3O7-δ matrix films. Higher rigidity was predicted for BaZrO3 1D-APCs than that of the BaHfO3 1D-APCs. This suggests a secondary APC doping of Y2O3 in the 1D-APC/YBa2Cu3O7-δ nanocomposite films would generate a stronger perturbation to the c-axis alignment of the BaHfO3 1D-APCs and therefore a more isotropic magnetic vortex pinning landscape. In order to experimentally confirm this, we have made a comparative study of the critical current density Jc (H, θ, T) of 2 vol.% BaZrO3 + 3 vol.%Y2O3 and 2 vol.%BaHfO3 + 3 vol.%Y2O3 double-doped (DD) YBa2Cu3O7-δ films deposited at their optimal growth conditions. A much enhanced isotropic pinning was observed in the BaHfO3 DD samples. For example, at 65 K and 9.0 T, the variation of the Jc across the entire θ range from θ=0 (H//c) to θ=90 degree (H//ab) is less than 18% for BaHfO3 DD films, in contrast to about 100% for the ...

Probing Microscopic Strain Interplay Due to Impurity Doping and Vicinal Growth and Its Effect on Pinning Landscape in YBCO Films

Pinning enhancement for YBa₂Cu₃O_7-δ (YBCO) thin films is critical for their future applications such as superconducting cables, generators, and motors. In this study, several pinning landscapes are introduced and compared for improving the superconducting properties of YBCO thin films. First, BaZrO₃ (BZO) nanoparticles have been doped into YBCO matrix providing uniform defect pinning centers and resulting in the superconducting property enhancement. Second, a magnetic nanocomposite of (La_0.7Sr_0.3MnO₃ (LSMO))_x(CeO₂ )_1-x (with compositions of LSMO and CeO₂ varied from 50:50 to 70:30) has been incorporated into YBCO as either a cap layer or a buffer layer. Using this approach, both magnetic pinning and defects pinning are introduced in the systems. Third, multilayers of (LSMO)_0.5(CeO₂)_0.5/YBCO have been deposited to achieve uniform defect and magnetic pinning effects through the film thickness. The superconducting properties (critical temperature T_c, and especially the critical current density J_c) are compared for all the YBCO films with different pinning landscapes, and the corresponding pinning mechanisms are also discussed for each case. It is found that the pinning effect of YBCO film with magnetic nanocomposite layer is more significant under lower applied field, compared to the BZO-YBCO film. Through this comparison study, optimum pinning landscapes with combined defects and magnetic pinning approaches are proposed.

Transformational dynamics of BZO and BHO nanorods imposed by Y2O3 nanoparticles for improved isotropic pinning in YBa2Cu3O7-δ thin films

Strong and isotropic vortex pinning landscape is demanded for high field applications of YaBa2Cu3O7-x (YBCO) epitaxial thin films. Double-doping (DD) of artificial pinning centers (APCs) of mixed morphologies has been identified as a viable approach for this purpose. This work presents a comparative study on the transport critical current density J c (H, θ) of 3.0 vol.%Y2O3+2.0 (or 6.0) vol.% BaZrO3 (BZO DD) and 3.0 vol.%Y2O3+ 2.0 (or 6.0) vol.% BaHfO3 (BHO DD) films. Based on the elastic strain model, BaHfO3 (BHO) nanorods have lower rigidity than their BaZrO3 (BZO) counterparts, which means their c-axis alignment is more susceptible to the local strain generated by the secondary dopant of Y2O3. Considering the increasing strain field with higher BZO (or BHO doping), the higher susceptibility may result in a large portion of the BHO APCs moving away from perfect c-axis alignment and enhancing isotropic pinning with respect to the H orientation. This is confirmed since the BHO DD films illustrate a less pronounced J c peak at H//c-axis and hence more isotropic J c(θ) than their BZO DD counterparts. At 9.0 T, the variation of the J c across the entire θ range (0-90 degree) is less than 18% for the BHO DD film, in contrast to about 100% for the 2.0 vol.% BZO DD counterpart. At the higher BHO concentration of 6.0 vol.%, this higher tunability of the Y2O3 leads to increased ab-plane aligned BHO APCs and hence enhanced J c at H//ab-plane.