Search

A detailed study on YBa2Cu3O7-δ (YBCO) films with BaZrO3(BZO) inclusions (YBCO-BZO) deposited on SrTiO3 substrate with different BZO contents is presented. X ray diffraction, SEM imaging and superconductive critical temperature (Ta) measurements were performed to evaluate film growth quality. Independently from the BZO content, all YBCO-BZO films showed Tc values close to that of pure YBCO indicating that the Tc reduction which is usually observed on YBCO-BZO films can be successfully recovered by changing the deposition conditions. All YBCO-BZO films showed an improved critical current density (Jc) dependence on magnetic field if compared to the typical Jc(H) of YBCO, resulting in higher irreversibility fields up to 9 T at 77 K. SEM observation on etched samples suggests a direct link between the defect density measured in YBCO-BZO samples and that calculated from the observed in field performances. The analysis of Jc(B) as a function of applied magnetic field direction revealed that the pinning due to isotropic pinning centers typical for YBCO is coupled with a c-axis correlated pinning in YBCO-BZO which can be ascribed to BZO induced columnar defects. Jc(B) recorded at several temperatures down to 10 K revealed matching effect features. [ABSTRACT FROM AUTHOR]

Much denser YBa2Cu3O7 (YBCO) superconducting films at least 1 μm thick with smooth surfaces have been obtained after introducing (Y/Nd)BCO multilayered structures. A significant enhancement of current carrying abilities has been achieved in these pulsed laser deposited films. The critical current density (Jc) has been increased by a factor of up to three in the entire field range. The imitation of the (Y/Nd)BCO multilayered structure by using YBCO ‘interlayers’ has also exhibited a considerable improvement in the current carrying ability. Similarities and differences between these two ‘multilayering’ approaches, leading to the observed effects, are discussed. The presence of interfaces even without element variation is likely to be the key to the improvements observed. In order to further promote Jc enhancement, small ‘multilayered’ additions of silver (Ag) to the films and multilayers provide various results: (i) rather strong enhancement for rather thin films and low addition levels, (ii) considerable degradation for large addition levels, and (iii) much less pronounced effect for thicker films. The enhancement of Jc is observed in zero and low magnetic fields, but has almost no effect at higher fields. All these experimental observations are discussed in terms of pinning, transparency and structural modifications introduced during the deposition of the film structures. [ABSTRACT FROM AUTHOR]

High temperature superconducting tapes based on cuprate compounds are nowadays available on long lengths by several companies. Because high superconducting properties are strongly influenced by the crystallographic orientation of the superconducting film, and because the appropriate crystallographic orientation is obtained through epitaxial film growth, the development of an oriented template is of crucial technological importance. In the rolling assisted biaxially textured substrate (RABiTS) technique, a strong cube texture is obtained by cold rolling fcc metal tape and high temperature annealing, followed by the deposition of one or more buffer layer by either physical vapor deposition (PVD) or chemical solution deposition (CSD). Using the latter approach, it has been recently shown that it is possible to combine substrate recrystallization and buffer layer growth in a single step if the onset of recrystallization occurs at a temperature lower than buffer layer nucleation. In the present contribution, a detailed investigation of biaxially-oriented La 2 Zr 2 O 7 (LZO) buffer layer grown on cold-rolled Ni-W substrate by combined EBSD, AFM and TEM analyses is reported. It is shown that it is possible to obtain highly {001}〈110〉-textured LZO film directly on cold-rolled Ni-W substrate. Although some small polycrystalline regions appear, this approach leads to a strong suppression of grain boundary grooving typically occurring in RABiT-type substrates. Further, it is shown that, notwithstanding the microstructure of the metal substrate continues to evolve during the conversion heat treatment, the obtained LZO film is well adherent, without cracks or delamination. [ABSTRACT FROM AUTHOR]

Abstract Bismuth telluride (Bi 2 Te 3) based alloys are preferred thermoelectric materials for room temperature thermoelectric applications. Electrical transport and thermopower properties of n-type nanostructured Bi x Sb 2-x Te 3 films were tuned by post-growth heat treatment. We report that annealing of sputter-deposited nanostructured Bi 0.7 Sb 1.3 Te 3 films lead to several-fold increases in thermoelectric power factor α2σ, where σ is electronic conductivity and α is Seebeck coefficient. Annealing at T anneal = 200 °C nearly quadruples the power factor to α2σ = 3.1 μW cm−1 K−2. Spectroscopy and microscopy analyses indicate that the power factor increase is attributable to ~50% decrease in the Bi/Sb ratio, and grain growth, which increase the charge carrier concentration and mobility. The observed Bi depletion is contrary to annealing-induced Te depletion reported in p-type films. For T anneal > 200 °C, although continued Bi depletion increases σ, a precipitous decrease in α sharply lowers the power factor, yielding tenfold lower α2σ for T anneal = 400 °C than the as-deposited films. Our findings indicate that post-deposition annealing is a potent way to tune the thermoelectric properties of n-type Bi 2 Te 3 -based alloy films to fabricate devices for high-efficiency solid-state refrigeration and power harvesting from waste heat. Graphical abstract Unlabelled Image Highlights • Compositional, microstructural and thermoelectric properties of nanostructured n-type bismuth antimony telluride (Bi x Sb 2-x Te 3) • Multifold enhancement in thermoelectric power factor (PF) in Bi x Sb 2-x Te 3 films • PF enhancement correlates with annealing-induced grain growth and Bi depletion. • Thermal annealing potent way to improve PF by tuning composition and microstructure [ABSTRACT FROM AUTHOR]