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  1. Abstract This work examines the pinning enhancement in BaZrO 3 (BZO) +Y 2 O 3 doubly-doped (DD) YBa 2 Cu 3 O 7 (YBCO) nanocomposite multilayer (DD-ML) films. The film consists of two 10 nm thin Ca 0.3 Y 0.7 Ba 2 Cu 3 O 7-x (CaY-123) spacers stacking alternatively with three BZO + Y 2 O 3 /YBCO layers of 50 nm each in thickness that contain 3 vol% of Y 2 O 3 and BZO doping in the range of 2–6 vol%. Enhanced magnetic vortex pinning and improved pinning isotropy with respect to the orientation of magnetic field (B) have been achieved in the DD-ML samples at lower BZO doping as compared to that in the single-layer counterparts (DD-SL) without the CaY-123 spacers. For example, the pinning force density ( F p ) of ∼58 GNm −3 in 2 vol.% of DD-ML film is ∼110% higher than in 2 vol% of DD-SL at 65 K and B // c -axis, which is attributed to the improved pinning efficiency by c -axis aligned BZO nanorods through diffusion of Calcium (Ca) along the tensile-strained channels at BZO nanorods/YBCO interface for improvement of the interface microstructure and hence pinning efficiency of BZO nanorods. An additional benefit is in the considerably improved J c ( θ ) and reduced J c anisotropy in the former over the entire range of the B orientations. However, at higher BZO doping, the BZO nanorods become segmented and misoriented, which may change the Ca diffusion pathways and reduce the benefit of Ca in improving the pinning efficiency of BZO nanorods. 
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  2. Abstract Microstructural analysis of the BaZrO 3 (BZO)/YBa 2 Cu 3 O 7 (YBCO) interface has revealed a highly defective and oxygen deficient 2-3 nm thick YBCO column surrounding the BZO one-dimensional artificial pinning centers (1D-APCs). The resulting semi-coherent interface is the consequence of the ∼7.7% BZO/YBCO lattice mismatch and is responsible for the low pinning efficiency of BZO 1D-APCs. Herein, we report an interface engineering approach of dynamic Ca/Cu replacement on YBCO lattice to reduce/eliminate the BZO/YBCO lattice mismatch for improved pinning at a wide angular range of the magnetic field orientation. The Ca/Cu replacement induces a local elongation of the YBCO c-lattice near the BZO/YBCO interface, thereby ensuring a reduction in the BZO/YBCO lattice mismatch to ∼1.4% and a coherent BZO/YBCO interface. This has resulted in enhanced pinning at B//c-axis and a broad angular range of B-field orientation. For example, the 6 vol.% BZO/YBCO film with interface engineering exhibits F p ∼158 GN/m 3 at 65 K and B//c-axis, which is 440% higher than the ∼36.1 GN/m 3 for the reference 6% BZO/YBCO sample, and enhanced J c and F p in a wide angular range up to ∼ 80°. This result illustrates a facile scheme for engineering 1D-APC/YBCO interface to resume the pristine pinning efficiency of the 1D-APCs. 
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  3. Abstract One-dimensional c -axis-aligned BaZrO 3 (BZO) nanorods are regarded as strong one-dimensional artificial pinning centers (1D-APCs) in BZO-doped YaBa 2 Cu 3 O 7− x (BZO/YBCO) nanocomposite films. However, a microstructure analysis has revealed a defective, oxygen-deficient YBCO column around the BZO 1D-APCs due to the large lattice mismatch of ∼7.7% between the BZO (3a = 1.26 nm) and YBCO (c = 1.17 nm), which has been blamed for the reduced pinning efficiency of BZO 1D-APCs. Herein, we report a dynamic lattice enlargement approach on the tensile strained YBCO lattice during the BZO 1D-APCs growth to induce c -axis elongation of the YBCO lattice up to 1.26 nm near the BZO 1D-APC/YBCO interface via Ca/Cu substitution on single Cu-O planes of YBCO, which prevents the interfacial defect formation by reducing the BZO/YBCO lattice mismatch to ∼1.4%. Specifically, this is achieved by inserting thin Ca 0.3 Y 0.7 Ba 2 Cu 3 O 7− x (CaY-123) spacers as the Ca reservoir in 2–6 vol.% BZO/YBCO nanocomposite multilayer (ML) films. A defect-free, coherent BZO 1D-APC/YBCO interface is confirmed in transmission electron microscopy and elemental distribution analyses. Excitingly, up to five-fold enhancement of J c ( B ) at magnetic field B = 9.0 T// c -axis and 65 K–77 K was obtained in the ML samples as compared to their BZO/YBCO single-layer (SL) counterpart’s. This has led to a record high pinning force density F p together with significantly enhanced B max at which F p reaches its maximum value F p,max for BZO 1D-APCs at B // c -axis. At 65 K, the F p,max ∼158 GN m −3 and B max ∼ 8.0 T for the 6% BZO/YBCO ML samples represent a significant enhancement over F p,max ∼ 36.1 GN m −3 and B max ∼ 5.0 T for the 6% BZO/YBCO SL counterparts. This result not only illustrates the critical importance of a coherent BZO 1D-APC/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO 1D-APCs. 
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  4. Abstract

    BaZrO3(BZO) one-dimensional artificial pinning centers (1D-APCs) aligned along thec-axis of the YBa2Cu3O7(YBCO) have been adopted to enhance the magnetic vortex pinning in BZO/YBCO nanocomposite films. However, the pinning force densityFpof the BZO 1D-APCs remains moderate at temperatures near 77 K. A hypothesis of the major limiting factor is the defective BZO 1D-APCs/YBCO interface as a direct consequence of the large interfacial strain originated from the BZO/YBCO lattice mismatch of ∼7.7%. Herein, we explore enlarging thec-axis of the YBCO dynamically to reduce the lattice mismatch and hence to prevent formation of the defective BZO 1D-APCs/YBCO interface. Specifically, thec-axis enlargement was achieved by partial replacement of Cu with Ca on the YBCO lattice using strain-directed Ca diffusion into YBCO from two Ca0.3Y0.7Ba2Cu3O7x(CaY-123) spacers of only 10 nm in thickness inserted into the 2 vol% BZO 1D-APC/YBCO nanocomposite thin films of ∼150 nm in total thickness. The achieved elongatedc-axis is attributed to the formation of stacking faults induced by Ca-replacement of Cu on YBCO lattice. The reduced BZO/YBCO lattice mismatch allows formation of a coherent BZO 1D-APC/YBCO interface with negligible defects. This leads to an enhancedFpvalue up to 98 GN m−3at 65 K, which is 70% higher than that of the reference 2 vol% BZO 1D-APC/YBCO sample. Furthermore, the benefit of the enhanced pinning of the BZO 1D-APCs with a coherent interface with YBCO can be extended to a large angular range of the magnetic field orientation. This study reveals the significant effect of the BZO/YBCO interface on the pinning efficiency of BZO 1D-APCs and provides a promising approach to achieve a coherent interface in BZO/YBCO nanocomposite films.

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  5. null (Ed.)
    Deposition temperature is an important parameter to control in pulsed laser deposition of thin films, as it affects the ad-atom mobility and diffusion in regards to film growth. Increased growth temperature can also result in increased stacking fault densities in YBa2Cu3O7- (YBCO) films. This research investigates the influence of deposition temperature on the critical current density, critical temperature, and the microstructure of YBCO thin films double doped with BaHfO3 and Y2O3. A KrF excimer laser was used to produce thin films of YBCO doped with 4 vol.% BaHfO3 and 3 vol. % Y2O3 on LaAlO3 (LAO) substrates at various deposition temperatures from 790 - 825. The growth temperature influence on the flux pinning landscape and Jc (H,T,) properties (T = 5 - 77K, H = 0 - 9T, = 0 -180) of these films will be presented. 
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