SECOND PHASE (BaGeO3, BaSiO3) NANOCOLUMNS IN YBa2Cu3O7-x FILMS
ADVANCES IN CRYOGENIC ENGINEERING (MATERIALS), VOL 56: TRANSACTIONS OF THE INTERNATIONAL CRYOGENIC MATERIALS CONFERENCE - ICMC
Authors: Varanasi, C. V.; Reichart, J.; Burke, J.; Wang, H.; Susner, M.; Sumption, M.; Barnes, P. N.
Abstract
YBa2Cu3O7-x (YBCO) films with BaGeO3 (BGeO), BaS1O(3) (BSiO) second phase additions were processed by pulsed laser deposition. Sectored targets with BGO or BSA) wedges as well as pre-mixed targets of YBCO, BGeO or BSI with appropriate compositions were used to deposit YBCO+BGeO and YBCO+BSIO films on (100) single crystal LaAlO3 substrates. The cross-sectional transmission electron micrographs showed the presence of 20 nm diameter nanocolumns in the YBCO films of both the compositions. However, the critical transition temperature (TO of the films was found to significantly decrease. As a result, the critical current density (Jr) in applied magnetic fields was suppressed. The YBCO+BGeO and YBCO+BSiO films made with lower concentrations of additions showed slight improvement in Te indicating that the substitution of Ge and Si in the lattice is possibly responsible for the T, depression. This study shows that in addition to the ability to form nanocolumns, the chemical compatibility of BaSnO3 (BSO) and BaZrO3 (BZO) as observed in YBCO+BSO and YBCO+BZO is critical to process high J(c), YBCO films
Effects of nanocrystalline target and columnar defects on flux pinning in pure and BaZrO3-doped YBa2Cu3O6+x films in fields up to 30 T
PHYSICAL REVIEW B
Authors: Peurla, M.; Huhtinen, H.; Shakhov, M. A.; Traito, K.; Stepanov, Yu. P.; Safonchik, M.; Paturi, P.; Tse, Y. Y.; Palai, R.; Laiho, R.
Abstract
Transport properties of YBa2Cu3O6+x films prepared by pulsed laser deposition from pure and BaZrO3- (BZO-)doped nanocrystalline targets and from a microcrystalline target are investigated in pulsed magnetic fields up to 30 T. As shown by transmission electron microscopy, doping by BZO creates columnar defects of diameter 5-10 nm traversing the films in the direction of the c axis. The irreversibility line, the delocalization line, and the high-field critical current density j(c) are strongly enhanced in the films deposited from a nanocrystalline target in comparison with those deposited from the microcrystalline target. Doping with BZO further improves the irreversibility and depinning lines and increases the value of j(c). The irreversibility fields of the films prepared from the pure and from the BZO-doped nanocrystalline targets exceed 10 T at 77 K, and at 65 K the value of j(c)approximate to 10(5) A/cm(2) is observed in fields up to 22 T.
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