Compatibility of Nd and Ba in YBa2Cu3Oy superconductor

A series of samples with nominal compositions of YBa2-xNdxCu3Oy were prepared by solid state reactions and investigated by X-ray diffraction, magnetic and electrical measurements. The solubility, x, was determined to be x0.3 Tc0 drops sharply to about 84 K, and finally for x=0.5 Tc on falls to 30 K and Tc0 is below 10 K. Our results suggest that the small compatibility of Nd and Ba in YBa2 Cu3Oy system does not seriously suppress the superconductivity.published_or_final_versio

Preparation and characterization of NdBa2Cu3O y thin films

C-axis oriented epitaxial NdBa2Cu3Oy thin films on (100) SrTiO3 substrates were prepared by off-axis rf sputtering. Thin films with Tc0=90 K in a deviation of 0.5 K were prepared reproducibly under the optimal depositing conditions. A parabolic relation of Tc0 to c-axis lattice parameter corresponding to a typical electronic phase diagram for high-Tc superconductors was observed, indicating an optimal oxygen content for the best superconductivity. The oxygen out-diffusion and thermal expansion of the films were studied by an in-situ high temperature x-ray diffraction.published_or_final_versio

Enhanced film quality of Y-Ba-Cu-O by using Eu-Cu-O buffer layer on Sr-Ti-O substrates

Eu2CuO4 (ECO) has been used as a buffer layer for growing of YBa2Cu3O7-δ (YBCO) thin films on SrTiO3 (STO) (100) substrates. The epitaxy, crystallinity and surface of YBCO thin films have been significantly improved by using ECO buffer layer as investigated by x-ray diffraction, rocking curves, scanning electron microscope, surface step profiler and x-ray small angle reflection. The best value of the full width at half maximum of the YBCO (005) peak can be greatly reduced down to less than 0.1 degree. The scanning electron microscope photos indicate very smooth surface for the YBCO thin films. The average roughness is less than 5 nm over a wide scanning region of 2000 μm. The results of x-ray small angle reflection indicate a very clear and flat interface between YBCO and ECO layers. Our results suggest that ECO should be a good barrier candidate for fabricating high-Tc superconductor junctions.published_or_final_versio

Preparation of continually graded barriers of YPrBaCuO for HTS Josephson junctions

We report preparation of a novel barrier structure for high Tc superconducting multilayer Josephson junctions using a simple composite target technique. Such a barrier consists of Yx Pr1-xBa2Cu3Oy with a continually varied concentration of yttrium. In this barrier no lattice mismatch and other incompatibility problems occur between adjacent layers. Thus the formation of interfacial defects and structural strain can be mostly prevented. The Josephson coupling takes place at the electrically formed interfaces rather than the structural interfaces. A particular feature of these junctions is that the effective thickness of the barrier strongly depends on the measuring temperature and the concentration gradient. The absence of the structural interface in the weak link region greatly enhances the reproducibility and the performance of these junctions.published_or_final_versio

Growth and characterization of Eu-Cu-O thin films on YSZ(100) substrates

High quality epitaxial Eu2CuO4 (ECO) thin films have been deposited on yttrium-stabilized zirconia (YSZ) (100) substrates by magnetron rf sputtering method. The obtained ECO films are highly c-axis-oriented and well crystallized, as shown by x-ray diffraction, rocking curves. The influence of oxygen out-diffusion on the c-axis length and the resistance behavior were studied. The post vacuum annealing removes the excess oxygen from the structure of ECO. As a result, the c-axis length decreases and the resistivity increases. By using ECO as a buffer layer, extremely smooth surface of YBCO was obtained on YSZ substrates.published_or_final_versio

Ultrathin films of YBaCuO grown on YSZ substrates with a new buffer layer Nd-Cu-O

YSZ is one of the most widely used substrates to grow oxide superconducting thin films. However, the large lattice mismatch and occurrence of intermediate layer often degrade the quality of grown films. We used a new buffer material, neodymium copper oxide (Nd2 CuO4), to improve the quality of YBCO ultrathin films grown on YSZ. Good superconducting transitions have been obtained on these films with thickness 10-12 nanometers. Such a Nd2CuO 4 layer has a stable crystal structure and behaves as an oxide semiconductor. At 77 K, its resistivity is ~40 times higher than that of PrBaCuO, which has been commonly used as buffer layer and barrier material. The lattice mismatch between Nd2CuO4 and YBCO is much smaller than that between YSZ and YBCO. It allows highly epitaxial growth of YBCO without forming big defects and the intermediate layer. Measurements by using XRD, rocking curve, and cross-sectional TEM indicated that the crystallinity of YBCO films grown on Nd2CuO4 buffer layer had been significantly improved. Besides, the smooth surface of Nd2CuO4 layer and buffered YBCO films are observed by SEM.published_or_final_versio

Excellent buffer layer for growing high-quality Y-Ba-Cu-O thin films

Eu2CuO4 (ECO) has been used as a buffer layer for growing of YBa2Cu3O7-ä (YBCO) thin films on SrTiO3(100) and Y-stabilized ZrO2(100) substrates. The epitaxy, crystallinity, and surface of YBCO thin films have been significantly improved by using ECO buffer layer as investigated by x-ray diffraction, rocking curves, scanning electron microscope, surface step profiler, and x-ray small-angle reflection. The best value of the full width at half-maximum of the YBCO(005) peak can be greatly reduced down to less than 0.1°. The scanning-electron-microscope photos indicate a very smooth surface for the YBCO thin films. The average roughness is less than 5 nm over a wide scanning region of 2000 ìm. The results of x-ray small-angle reflection indicate a very clear and flat interface between YBCO and ECO layers. Meanwhile, the resistivity of ECO is about 20 times higher than that of PrBa2Cu3Oy at the boiling point of liquid nitrogen. Our results suggest that ECO should be a good barrier candidate for fabricating high-Tc superconductor junctions.published_or_final_versio

High-Tc ramp-type Josephson junctions with a continually graded Y1–xPrxBa2Cu3Oy barrier

High-Tc Josephson junctions with a graded barrier have been prepared by using a composite target. Such a barrier is synthesized by utilizing Y1–xPrxBa2Cu3Oy with a continually graded concentration of Pr, in which no lattice mismatch and other incompatible problems take place. The structural interfaces are absent in the weak link region and Josephson coupling occurs at the naturally formed superconducting/normal interfaces within the Y1–xPrxBa2Cu3Oy layer. Thus, it can significantly enhance the reproducibilty and performance of these junctions. The temperature dependences of the barrier thickness and Josephson were also studied. © 2001 American Institute of Physics.published_or_final_versio

Antioxidant properties of banana flower of two cultivars in China using 2,2-diphenyl-1-picrylhydrazyl (DPPH,) reducing power, 2,2’-azinobis-(3-ethylbenzthiazoline-6- sulphonate (ABTS) and inhibition of lipid peroxidation assays

In this study, the antioxidant properties of banana flower extracts (cvs. Baxijiao (AAA) and Paradisiaca (AAB)) were analysed by using several biochemical assays which include 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, reducing power, 2, 2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate (ABTS) radical scavenging activities and inhibition of lipid peroxidation in egg lecithin through the formation of thiobarbituric acid-reactive substances (TBARS). These assays have been extensively studied and generally accepted as models to characterize peroxidative damage in biomembranes. In the present study, the EC50 values were calculated using each method as listed above was used to compare the antioxidant efficiency of each banana flower extract. The phenol, flavonoid, vitamin E and saponin contents were also analyzed. Baxijiao flower extract revealed better antioxidant properties by presenting much lower EC50 values, particularly for reducing power. In addition, antioxidant concentrations (polyphenols and flavonoids) were found higher in this flower sample than those in the Paradisiaca sample. The results suggested that the Baxijiao flower could be a better resource either as a dietary supplement or as a food additive than the later one.Key words: Banana flower, antioxidant, scavenging effects, peroxidation

Molecular Diversity and Potential Anti-neuroinflammatory Activities of Cyathane Diterpenoids from the Basidiomycete Cyathus africanus

Ten new polyoxygenated cyathane diterpenoids, named neocyathins A-J (1-10), together with four known diterpenes (11-14), were isolated from the liquid culture of the medicinal basidiomycete fungus Cyathus africanus. The structures and configurations of these new compounds were elucidated through comprehensive spectroscopic analyses including 1D NMR, 2D NMR (HSQC, HMBC, NOESY) and HRESIMS, and electronic circular dichroism (ECD) data. Neuroinflammation is implicated in the pathogenesis of various neurodegenerative diseases, such as Alzheimers' disease (AD). All isolated compounds were evaluated for the potential anti-neuroinflammatory activities in BV2 microglia cells. Several compounds showed differential effects on the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in lipopolysaccharide (LPS)-stimulated and Aβ1-42-treated mouse microglia cell line BV-2. Molecular docking revealed that bioactive compounds (e.g., 11) could interact with iNOS protein other than COX-2 protein. Collectively, our results suggested that this class of cyathane diterpenoids might serve as important lead compounds for drug discovery against neuroinflammation in AD.published_or_final_versio