Tailoring Microstructure and Superconducting Properties in Thick BaHfO3 and Ba2 Y(Nb/Ta)O6 Doped YBCO Films on Technical Templates

Abstract

The current transport capability of YBa 2 Cu 3 O 7 −x (YBCO) based coated conductors (CCs) is mainly limited by two features: the grain boundaries of the used textured template, which are transferred into the superconducting film through the buffer layers, and the ability to pin magnetic flux lines by incorporation of defined defects in the crystal lattice. By adjusting the deposition conditions, it is possible to tailor the pinning landscape in doped YBCO in order to meet specific working conditions (T, B) for CC applications. To study these effects, we deposited YBCO layers with a thickness of about 1-2 μm using pulsed laser deposition on buffered rolling-assisted biaxially textured Ni-W substrates as well as on metal tapes having either an ion-beam-textured YSZ buffer or an MgO layer textured by inclined substrate deposition. BaHfO 3 and the mixed double-perovskite Ba 2 Y(Nb/Ta)O 6 were incorporated as artificial pinning centers in these YBCO layers. X-ray diffraction confirmed the epitaxial growth of the superconductor on these templates as well as the biaxially oriented incorporation of the secondary phase additions in the YBCO matrix. A critical current density J c of more than 2 MA/cm² was achieved at 77 K in self-field for 1-2 μm thick films. Detailed TEM (transmission electron microscopy) studies revealed that the structure of the secondary phase can be tuned, forming c-axis aligned nanocolumns, ab-oriented platelets, or a combination of both. Transport measurements show that the J c anisotropy in magnetic fields is reduced by doping and the peak in the J c (θ) curves can be correlated to the microstructural features.Index Terms-Alternating beam assisted deposition (ABAD), coated conductors, inclined substrate deposition (ISD), pinning, pulsed laser deposition, RABiTS, YBa 2 Cu 3 O 7 −x (YBCO).

Influence of Substrate Tilt Angle on the Incorporation of BaHfO3 in Thick YBa2Cu 3O7‐δ Films

“…The peaks broaden with increasing vicinal angle (full width at half maximum for YBCO (005): 0.29° for α=0°, 0.67° for α=40°), whereas the c-axis parameter decreases almost linearly from 11.83 Å for α=0° to 11.73 Å for α=40°. The BHO (400) and Y 2 O 3 (400) peaks are shifted from their theoretical position and have an non-symmetrical shape, which might be explained by the incorporation of Y in BHO or Hf in Y 2 O 3 , respectively [3], [5], [8]. For the sample on the 30° tilted ISD-MgO template, the BHO peak is overlapped by the strong MgO (200) buffer layer peak.…”

“…5(c)+(d)) indicate the influence of the tilt on the local microstructure resulting in a change from c-axis parallel nanorods to ab-planar structures with increasing vicinal angle. Whereas structures parallel to the c-axis are only formed on flat surfaces (similar to ABAD-YSZ-buffered templates in [5]), a mixed microstructure containing short columns parallel to c YBCO as well as planes parallel to the abplane are formed for α = 2 to 5°. With higher tilt, the columns disappear and tilted platelets are the predominant form of secondary phases as observed for the highly tilted films on ISD-tapes (cf.…”

“…We have realized self-assembled BaHfO 3 (BHO) nanocolumns oriented parallel to the c-axis in thick YBCO films on technical Ni-W RABiT substrates [2], [3] as well as on IBAD-YSZ textured tapes [4] with improved in-field performance for B||c YBCO . Here, length, dimension and splay of the nanoprecipitates can be tailored by careful adjustment of key parameters such as growth rate (R), deposition temperature (T S ) and doping level [5]. In contrast, it is challenging to grow self-assembled nanocolumns in doped YBCO films on inclined substrate deposition (ISD)-MgO buffered tape.…”

“…no B||c peak appears in angle-dependent J c measurements of such samples [6]. TEM investigations show the formation of alternating YBCO layers and BHO/Y 2 O 3 platelets which are aligned parallel the YBCO ab-plane [5], [6]. In this work, we studied the influence of the vicinal angle α of miscut SrTiO 3 (mSTO) single crystal substrates on the growth mode of nanosized BHO structures in thick YBCO films.…”

Ultra-high critical current densities of superconducting YBa2Cu3O7-δ thin films in the overdoped state

“…In case of CSD, the stoichiometric amount of precursor metal trifluoroacetate salts is dissolved in an alcoholic solution and deposited by spin-coating, followed by a pyrolysis (∼300 °C) and growth (∼800 °C) temperature treatment at P O2 = 0.2 mbar 73 , 74 . PLD layers are deposited at 800 °C at P O2 = 0.3 mbar with a pulse frequency of 5 Hz 75 . The PLD-targets were fabricated by Oxolutia SL (Spain) and consist of pressed and sintered, stoichiometric YBCO powder at 87% density.…”