Sansheng WANG
,
Lin WANG
,
Bingfu GU
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材料科学技术（英）
A full solution method has been developed as a low cost process of YBa2Cu3O7-x (YBCO) coated conductor fabrication. In this study, highly biaxially textured SrTiO3 (STO) buffer layers were fabricated on LaAlO3 (LAO) single crystal substrates by sol-gel method using metal alkoxides as the staring precursor materials. High quality YBCO superconducting film was then fabricated on STO-buffered LAO substrate by trifluoroacetic metalorganic deposition (TFA-MOD) method. For the YBCO superconducting film, only (00l) diffraction peaks can be detected by XRD (X-ray diffraction) analysis with no other phases detectable. Especially, In-plane texture of YBCO film is improved compared to that of STO buffer layer from phi scans analysis, which indicates the self-epitaxy phenomenon explained by considering interfacial energy. STO and YBCO films both
show c-axis oriented grains growth and have uniform surface microstructure. A critical transition temperature, Tc (R=0) of 89.5 K and a critical current density of 2 mA/cm2 (77 K, self-field) were obtained for a 0.2 μm thick YBCO film on STO-buffered LAO substrate. No reaction between YBCO and STO was detected by XRD analysis. This full solution process may provide a promising low cost fabrication route for YBCO coated conductors on metal tape.
关键词:
YBCO coated conductor
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Jun ZHANG
,
Qian LIU
,
Lin WANG
材料科学技术（英）
Fine and coarse aggregates play an important role in the fracture of concrete. However, quantitative information available on the effect of the coarse aggregate size on the fracture properties of concrete is still limited. In the present paper, the effect of coarse aggregate size (single grade of 5～10, 10～16, 16～20 and 20～25 mm) on stress-crack opening (σ-ω) relation in normal and high strength concretes (compressive strength of 40 and 80 MPa, respectively) was studied. The investigation was based on three-point bending tests implemented by fictitious crack analysis. The result shows that coarse aggregate size and cement matrix strength significantly influence the shape ofσ-ω curve. For a given total aggregate content, in normal strength concrete, smaller size of aggregate leads to a high tensile strength and a sharp stress drop after the peak stress. The smaller the coarse aggregate, the steeper the σ-ωcurve. By contrast, in high strength concrete, the effect of aggregate size on σ-ω relation almost vanishes. A similar σ-ω relation is obtained for the concrete except for the case of 20～25 mm coarse aggregate size. The stress drop after the peak stress is more significant for high strength concrete than that for normal strength concrete. Meanwhile, the smaller the coarse aggregate size, the higher the flexural strength. Fracture energy and characteristic length increase with increasing coarse aggregate size in both normal and high strength concretes.
关键词:
Aggregate size
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