YBa₂Cu₃O_7−x films with Ba₂Y(Nb,Ta)O₆ nanoinclusions for high-field applications

Abstract

Structural and transport properties of YBa 2 Cu 3 O 7-x films grown by pulsed laser deposition with mixed 2.5 mol.% Ba 2 YTaO 6 (BYTO) and 2.5 mol.% Ba 2 YNbO 6 (BYNO) double-perovskite secondary phases are investigated in an extended film growth rate, R = 0.02 -1.8 nm/s. The effect of R on the film microstructure analyzed by TEM techniques shows an evolution from sparse and straight to denser, thinner and splayed continuous columns, with mixed BYNO+BYTO (BYNTO) composition, as R increases from 0.02 nm/s to 1.2 nm/s. This microstructure results in very efficient flux pinning at 77 K leading to a remarkable improvement of the J c behaviour, with the maximum of the pinning force density F p (Max) = 13.5 GN/m 3 and the irreversibility field in excess of 11 T. In this range, the magnetic field values at which the F p , is maximized varies from 1 T to 5 T being related to the BYNTO columnar density. The film deposited with R = 0.3 nm/s exhibits the best performances over the whole temperature and magnetic field ranges achieving F p (Max) = 900 GN/m 3 at 10 K and 12 T. At higher rates, R > 1.2 nm/s, BYNTO columns show a meandering nature and are prone to form short nanorods. In addition, in the YBCO film matrix a more disordered structure with a high density of short stacking faults is observed. From the analysis of the F p (H, T) curves it emerges that in films deposited at the high R limit, the vortex pinning is no longer dominated by BYNTO columnar defects, but by a new mechanism showing the typical temperature scaling law. Even though this microstructure produces a limited improvement at 77 K, it exhibits a strong J c improvement at lower temperature with F p = 700 GN/m 3 at 10 K, 12 T and 900 GN/m 3 at 4.2 K, 18 T.

Simultaneous achievement of high J c and suppressed J c anisotropy by hybrid pinning in YBa2Cu3O7 three-phase-nanocomposite film

“…Nanorods and nanoparticles pin vortices in different manners and their combination leads to hybrid pinning. Although high J c properties are being reported [22,24], further J c improvement is required in this hybrid pinning system. This hybrid pinning system is a complicated three-phase-nanocomposite (matrix, nanorods, and nanoparticles).…”

Self-Organized Nanocomposite Structure Controlled by Elemental Site Occupancy to Improve Vortex Pinning in YBa2Cu3O7 Superconducting Films

“…For further control of these parameters, BaSnO 3 (BSO), BaHfO 3 (BHO), − and double perovskite oxides such as Ba 2 YNbO 6 (BYNO) − have been investigated as the nanorod material. Furthermore, the Y 2 O 3 nanoparticles have been additionally incorporated into YBCO+BaMO 3 (BMO; M = Zr, Sn, Hf) films to achieve the hybrid pinning. − This kind of hybrid pinning structure is sometimes self-organized when the double perovskite is incorporated in the YBCO films to form the nanorods. − The addition of Ba 2 Y­(Nb,Ta)­O 6 to a mixture of Nb and Ta controls not only the hybrid pinning but also the strain …”

Overcoming optimization constraint for J c by hybrid pinning in YBa2Cu3O7 films containing nanorods

“…[2][3][4] Since nanorods can realize very high J c , structural optimization is being performed. BaZrO 3 (BZO), 5,6) BaSnO 3 (BSO), 7) BaHfO 3 (BHO), 8-10) Ba 2 YNbO 6 , 11) Ba 2 Y(Nb/Ta)O 6 12) etc have been investigated as a nanorod material to control structure of nanorods. A density of c-axis correlated pinning centers is an important parameter to control the c-axis correlated pinning of columnar defects 13,14) and nanorods, 15,16) and a volume fraction of nanorods is dominant to the nanorod density.…”