Phase Compatibility and Superconductivity of Y-Ba-Cu-O Compounds

Abstract

Superconducting properties of Y-Ba-Cu-O compounds were investigated in relation to precipitation of second phases. Contour lines of J c, T c and diamagnetic signal intensities were presented in the YO1.5-BaO-CuO system. These superconducting properties decreased steeply with BaCuO2 precipitation, and the maximum J c was obtained in the yttrium-rich composition of Y1.2Ba2Cu3O7-y . It is considered, therefore, that the BaCuO2 precipitating around the YBa2Cu3O7-y grains interrupt the superconducting current pass at the grain boundary. Yttrium-rich composition, which inhibits BaCuO2 precipitation, is effective for the preparation of the high-J c sample.

Powder melting process for superconductor by eutectic formation

“…Therefore, Ag addition may be either advantageous or disadvantageous depending on the Ag distribution within the sample and its degree of dissolution in the other raw materials. This is in agreement with previous studies [6,11] in which the role of Ag was reported to be strongly dependent on the processing techniques and their liquid-forming temperatures. If Ag is to be used as an effective sintering and microstructural aid for YBa 2 Cu 3 O 7−y superconductors, then it is crucial that the initial liquid-formation temperature be lowered, through control of the starting materials, to below the Ag melting point (961…”

“…The reproducibility of composition and physical properties of the melt-textured YBa 2 Cu 3 O 7−y samples was poor even after the addition of Ba to the initial raw materials (composition f) sintered on alumina substrates. Addition of BaCuO 2 to the raw materials to compensate for Ba depletion was not successful because the BaCuO 2 easily forms a secondary phase which tends to accumulate at the grain boundary and consequently impedes the YBa 2 Cu 3 O 7−y grain growth [6]. This result is contradictory to a previous study in which addition of BaCuO 2 in the raw materials could be used as a catalyst for YBa 2 Cu 3 O 7−y grain growth [7].…”

“…Owing to the high reaction temperatures required by these methods, typically above ∼1000 • C, the liquid formed during the peritectic reaction tends to react with the surrounding materials, such as substrates. For this reason, much work has been done in an attempt to lower the liquid formation temperature [6,7]. Melting at the eutectic point, in particular, appears to be an attractive approach.…”

(RE)Ba2Cu3O7 Coated Conductors for AC and DC Applications

“…Because the detrimental effect of grain boundaries on the current percolation is limited to lower operation temperature and magnetic fields below H Fig.32a) [94]. …”