Alignment of YBa2Cu3O7‐xand Ag─YBa2Cu3O7‐xComposites at ∼930°C by Eutectic Formation

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Abstract
The present work describes a new technique to synthesize aligned YBa2Cu3O7‐xand Ag─YBa2Cu3O7‐xsuperconducting composites from Ba‐ and Cu‐deficient compositions (relative to YBa2Cu3O7‐x) plus BaCuO2. For YBa2Cu3O7‐x, high transition temperature midpointTc(91 K), temperature of zero resistivityT0(90 K), and critical current densityJc(>3000 A°Cm−2at 77 K) were achieved by using this technique. This procedure provides the potential for using a reliable and reproducible densification and alignment technique alternative to partial or full melting. The composite is highly aligned, with an average grain size of ∼1 to 2 mm and domains of width greater than 5 mm. The initial phase assemblage consists of YBa2Cu3O7‐x(123) as the major phase plus YBa2CuO5(211) CuO as minor phases. The BaCuO2is added to the Ba‐ and Cu‐deficient starting composition in order to assist in the formation of a CuO‐rich liquid as well as to compensate for the Ba and Cu deficiences in 123. Since the liquid forms at ∼900°C and is compatible with 123, it can be used to facilitate alignment of 123 at ∼930°C. The addition of Ag to the system results in eutectic formation with the (solidified) liquid, substantial filling of the pores during sintering, and improved alignment.