Materials Science Forum Vols. 546-549

Abstract: A superconductor-polymer composite of Bi1.8Pb0.4Sr2Ca2Cu3Oy and ethylene propylene rubber (EPR) was prepared by conventional solid-state reaction method. The phase structure of the composite was characterized by using x-ray diffraction technique. The resistivity of composite samples annealed at different temperatures was measured between 40K and 300K. The results indicate that the resistivity of the as-prepared composite increases with increasing EPR content and shows essentially a semiconducting behavior above Tc. For fixed EPR content, the resistivity of composite samples decreases with increasing annealing temperature. The composite begins to show some signs of superconducting transition at an annealing temperature of 700 °C and zero resistance is reached for samples sintered at 800°C. Thermal gravimetric analysis (TGA) on the composite confirmed that 65% of the EPR content still present in the superconducting composite samples. SEM was used to investigate the surface morphology of the composites. Preliminary results show that the mechanical properties of the composite have been much improved compared with its parent superconductor ceramics.

Abstract: Influence of cold rolling total thickness reduction, annealing temperature and annealing time on the textures in powder metallurgic Ni-5at.%W substrate tapes have been quantitatively investigated with the EBSD (Electron Back-Scattered Diffraction) technique. A “copper” type-like texture consisting of {1 2 3}<6 3 –4>+{0 1 –1}<3 –1 –1>+{1 –1 2}<1 –1 –1> has been found in the as-rolled tapes. This texture was much intensive in the tape at 99% thickness reduction than in the tape at 87% thickness reduction. The 99% reduction tape showed a higher fraction and sharper cube texture than the 87% reduction tape after annealing treatment. In addition, annealing at 1000°C was much favourable for the cube texture formation than annealing at 950°C and resulted in a higher cube texture fraction.

Abstract: with yttrium, barium, copper acetates as starting materials, a low-fluorine-content solution was prepared. YBa2Cu3O7-x (YBCO) films on LaAlO3 (LAO) single crystal substrates were fabricated by a new TFA-MOD method. Solution-derived YBCO films exhibited epitaxial growth, which was confirmed by X-ray diffraction (XRD). The humidity of the furnace atmosphere during annealing process influences the texture of YBCO film. Under high-humidity of furnace atmosphere, a-oriented grains, which were confirmed by scanning electron microscopy (SEM), were generated on film surface. High-resolution transmission electron microscopy (HRTEM), however, indicated that although a-axis oriented grains formed on the film surface, c-axis oriented grains occupied the area near the YBCO/LAO interface. High-performance YBCO films with Tc above 90K, and Jc more than 106A/cm2 at 77 K and zero magnetic field were obtained.

Abstract: precursor solution was prepared using barium trifluoroacetae (Ba-TFA) and non-fluorine yttrium (Y) and copper (Cu) organic salts. The precursor solution was modified by benzalacetone (BzAcH), in which the Cu2+ were chelated with BzAcH, which preventing the loss of Cu in the pyrolysis process. Dense YBCO superconducting films with smooth surface, which confirmed by scanning electron microscopy (SEM), were repeatedly obtained through sol-gel process. X-ray diffraction (XRD) 2θ scanning and φ scanning indicated that the as-prepared YBCO films had good c-axis texture. YBCO films with superconducting transition temperature (TC) above 89K were obtained.

Abstract: CeO2 has been considered as one of the most lattice compatible and chemically stable materials for YBa2Cu3O7-x coated conductors. In this paper, we presented the epitaxial growth of CeO2 thin film on both YSZ single crystal and cube textured Ni5W substrates by MOD method. Homogenous, crack-free and dense CeO2 thin films on both substrates with sharp biaxially cube texture were fabricated by post-annealing the precursor films at 1000-1150°C. For the CeO2 film on the textured Ni5W substrate, the FWHM values of (111) Phi-scan and (002) rocking curve were around 6°and 7°, respectively, the surface roughness was less than 2 nm over an area of 1μm×1μm observed by AFM. It was found that the CeO2 thin film improved both the in-plane orientation and surface roughness of the Ni5W substrate, indicating that the as deposited CeO2 films were suitable for the further growth of YBCO superconductor layer.

Abstract: It is well know that Ni-5at.% W(Ni5W) and Ni-9.3at.% W(Ni9W) alloy substrates are two kinds of promising materials to be employed in coated conductors. The Ni5W substrate is very easy to produce cube texture, while the Ni9W alloy has a lower magnetic property and higher strength. However, the pure cube texture are not capable to be obtained in Ni9W alloy. In this work, the preparation and texture development in both Ni5W and Ni9W alloy substrates have been reported. Highly biaxial textured Ni5W substrate was fabricated by cold rolling, followed by three different annealing routes. The texture analysis indicated that a sharp cube texture was formed after annealing at a wide temperature range of 800-1100°C in as rolled Ni5W substrate. The high quality of cube orientation was obtained after a two step annealing (TSA) with farthing twin boundaries analyzed by EBSD. Furthermore, in order to obtain a pure cube texture in Ni9W alloy substrate, a typical rolling process was performed and the deformation texture was optimized in these substrates. The designed deformation texture components were obtained in Ni9W alloy when pre-heating the ingot at 250 °C before performing a cold rolling, which shows a possibility to form cube texture in Ni9W alloy substrate after annealing.

Abstract: The Te doped NbSe2-xTex (x=0, 0.10, 0.20) single crystals were prepared by vapor transport method and the variations of structure and superconducting properties with Te content were studied. It is found that the Te substitution increases the degree of disorder and causes sharp decrease of superconducting transition temperature (Tc). The temperature dependence of upper critical field (Hc2) of pure NbSe2 crystal can be fitted by the two-band model, and the effect of Te substitution on Hc2(T) is discussed.

Abstract: Nb3Sn superconductors are widely used in high magnetic field application. Internal tin processed Nb3Sn wires used for ITER coils (at 4.2K, 12T) were heated by two steps, local heat treatment and reaction heat treatments. The superconducting properties of Nb3Sn were investigated as a function of reaction heat treatment (HT) for strands during 625°C~665°C.To study the heat treatment effects on Jcn and n-value of Nb3Sn strands, different HT-parameters, i.e., annealing temperature and times, were applied on the Nb3Sn multifilament strands.

Abstract: MgB2 thin films have been coated on Nb substrates without any buffer layers. An in situ pulsed laser deposition (PLD) method was used to prepare the coating. The interface between films and substrates has been characterized by scanning electron microscopy (SEM). Surface impedance has been measured for the MgB2 films on Nb substrates. The results were discussed with regard to the potential large scale applications in superconducting RF cavities.