Retaining a dissipation-free state while carrying large electrical currents is a challenge that needs to be solved to enable commercial applications of high-temperature superconductivity. Here, we show that the controlled combination of two effective pinning centres (randomly distributed nanoparticles and self-assembled columnar defects) is possible and effective. By simply changing the temperature or growth rate during pulsed-laser deposition of BaZrO(3)-doped YBa(2)Cu(3)O(7) films, we can vary the ratio of these defects, tuning the field and angular critical-current (Ic) performance to maximize Ic. We show that the defects' microstructure is governed by the growth kinetics and that the best results are obtained with a mixture of splayed columnar defects and random nanoparticles. The very high Ic arises from a complex vortex pinning landscape where columnar defects provide large pinning energy, while splay and nanoparticles inhibit flux creep. This knowledge is used to produce thick films with remarkable Ic(H) and nearly isotropic angle dependence.

Metal oxides are emerging as important materials for their versatile properties such as high-temperature superconductivity, ferroelectricity, ferromagnetism, piezoelectricity and semiconductivity. Metal-oxide films are conventionally grown by physical and chemical vapour deposition. However, the high cost of necessary equipment and restriction of coatings on a relatively small area have limited their potential applications. Chemical-solution depositions such as sol-gel are more cost-effective, but many metal oxides cannot be deposited and the control of stoichiometry is not always possible owing to differences in chemical reactivity among the metals. Here we report a novel process to grow metal-oxide films in large areas at low cost using polymer-assisted deposition (PAD), where the polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and the formation of uniform metal-organic films. The latter feature makes it possible to grow simple and complex crack-free epitaxial metal-oxides.

Epitaxial c-axis oriented BiFeO3 (BFO) thin films were deposited on conductive SrRuO3 (SRO) on (001) SrTiO3 substrates by pulsed laser deposition. A Pt/BFO/SRO capacitor was constructed by depositing a top Pt electrode. The leakage current density versus. electric field characteristics were investigated from 80to350K. It was found that the leakage mechanisms were a strong function of temperature and voltage polarity. At temperatures between 80 and 150K, space-charge-limited current was the dominant leakage mechanism for both negative and positive biases. On the other hand, at temperatures between 200 and 350K the dominant leakage mechanisms were Poole-Frenkle emission and Fowler-Nordheim tunneling for negative and positive biases, respectively.

During the development of YBa2Cu3O7−δ (YBCO) coatings on flexible metal tapes, it has become evident that the achievable critical current (Ic) reaches a maximum value of about 200 A per cm of conductor width at a coating thickness of 1–2 μm. Additional YBCO beyond this thickness can actually reduce Ic. To investigate, critical current density (Jc) has been measured for samples with YBCO ranging from 0.39 to 6.3 μm in thickness. Several films were thinned by ion milling and remeasured with two significant results: almost no supercurrent is carried at thickness levels above 2 μm; and for films thicker than 3 μm, Jc is drastically reduced near the substrate as well.

IntroductionIn the area of second-generation hightemperature superconductor (HTS) wires, there are vigorous programs that have been undertaken by various institutions and consortia to develop long lengths of highquality superconducting tape using costefficient manufacturing techniques. The methodologies employed include diverse processes used to fabricate YBa 2 Cu 3 O 7-␦ (YBCO) HTS films as well as the biaxially textured template platforms on which the superconducting films are deposited.Ion-beam-assisted deposition (IBAD) of cubic metal oxide films is one of the approaches being pursued to form such textured templates. Within the IBAD research community, there have been many different cubic metal and metal oxide materials that have been demonstrated to be biaxially textured to some degree. Two of these that are currently being used as templates for long-length coated conductors are yttrium-stabilized zirconia (YSZ) and gadolinium zirconate (GZO). These are described in the article by Iijima et al. in this issue. A third template, magnesia (MgO), is the focus of this article. Before discussing IBAD-MgO and its specific advantages and disadvantages relative to the other IBAD templates, it is useful to briefly review the history of ion-beam processing methods employed to texture films. Early History of Ion-Beam TexturingExperimental studies of the penetration of medium-energy ions (15-75 keV) in single crystals of fcc metals (Au and Al) found that the ion-penetration ranges decrease sequentially along the [110], [100], and [111] crystallographic directions, respectively. 1-3 Computer simulations using Born-Mayer potentials to describe the range variations with crystallographic orientation of 5 keV Cu atoms in fcc Cu single crystals corroborated the experimental penetration distributions observed for Au and Al. 4 It was concluded that channeling processes along the principal axes of fcc crystal lattices were responsible for the qualitative resemblance between the experimental and calculated penetration range results. 2,3 Analyses were also performed for 1-10 keV Cu atoms incident on various crystallographic directions of fcc, diamond, and bcc lattices. 5 These calculations resulted in an ordering of the channeling range dependencies for the Cu atom penetrations as a function of direction and lattice type. For the three lattice types studied, this ordering is illustrated in Table I, with the range variations listed in order from highest to lowest for the three lowindex directions. Sputter experiments using Cu and Ag single crystals for 1-10-keV Ar ions impacting within a few degrees of the three low-index planes found that the sputter yields progress from lowest to highest for the [110], [100], and [111] directions, respectively. 6 These sputter yield versus crystalline orientation results agreed with the predicted range variations for the fcc lattices, in that the probability of atoms being sputtered from a material is greater if the collisions between the incident ions and the atoms of the solid occur nearer to it...