Showing papers by "S. R. Foltyn published in 2002"

High-temperature superconducting thick films with enhanced supercurrent carrying capability

Abstract: We have developed a multilayer architecture to enhance the supercurrent carrying capability of thick (>1 μm) YBa2Cu3O7−x (YBCO) films. An interlayer of CeO2, which functions as a starting template for growth of subsequent high-quality YBCO layers, is used to prohibit the generation of microstructural defects that otherwise develop in the top region of thick YBCO films. Improved surface quality for a 3.3 μm thick YBCO film has been confirmed by the channeling data of Rutherford backscattering spectroscopy and by scanning electron microscopy. Compared to our routinely prepared single-layer YBCO thick film in which the supercurrent drops rapidly with increasing film thickness, this multilayer makes it possible to maintain critical current density over 1 MA/cm2 with less restrictions on the thickness of coated conductors.

Role of SrRuO3 buffer layers on the superconducting properties of YBa2Cu3O7 films grown on polycrystalline metal alloy using a biaxially oriented MgO template

Abstract: A SrRuO3 (SRO) buffer layer has been developed for growth of superconducting YBa2Cu3O7 (YBCO) thick films on polycrystalline metal substrates where a biaxially oriented MgO layer—produced by ion-beam-assisted deposition (IBAD)—was used as a template. By using such an architecture, we have routinely deposited YBCO films with an in-plane mosaic spread in the range of 3°–6° in full width at half maximum. A critical current density of 3.0×106 A/cm2 in self-field at 75 K for a film thickness of over 1.3 μm has been achieved. We believe that the SRO buffer layer plays a significant role in the much improved performance of YBCO conductors built on IBAD MgO. The features of SRO, such as good lattice match with both MgO and YBCO, excellent thermal stability in an oxidizing environment, and planarization of growing surface, make it the ideal choice as the buffer layer for high-performance superconductor coatings.

Ca doping of YBCO grain boundaries

Abstract: Ca-gels were applied to highly dense YBCO pellets and PLD thin films followed by high temperature post-annealing. Parameters of Ca diffusion in YBCO (diffusion coefficients, activation energy, etc.) as a function of temperature and oxygen partial pressure were determined by depth profiling SIMS. Fast Ca diffusion along the grain boundaries was observed by FIB and SIMS. The effect of Ca doping on Tc and Jc was studied by VSM. Ca distribution in the samples, induced by preferential diffusion along the grain boundaries, did not appear to change superconducting properties within the grains but showed increased Jc across the grain boundaries.

Characterization of superconducting SmBa2Cu3O7 films grown by pulsed laser deposition

Abstract: We have investigated epitaxial superconducting SmBa2Cu3O7 (Sm123) films grown by pulsed-laser deposition on single-crystal SrTiO3 substrates. The deposition temperature plays an important role in determining the superconducting properties of Sm123 films. The superconducting transition temperature increases with the deposition temperature whereas the transition width decreases at deposition temperatures in the range of 700–875 °C. A Sm123 film deposited at 850 °C exhibits a transition temperature above 93 K with a transition width less than 0.5 K. Even though Sm123 films exhibit a higher transition temperature than Yba2Cu3O7 (Y123), the Sm123 shows lower critical current density at liquid-nitrogen temperature. The nominal critical current density of Sm123 film is less than 1 MA/cm2 at 75.4 K. Nevertheless, the Sm123 films have less anisotropy and stronger pinning characteristics compared to Y123. They are also much smoother with fewer particulates, as revealed by scanning electron microscopy.