Formation of Y₂Ba₄Cu₇O_y at Ambient Pressure

Abstract

Preparation of Y₂Ba₄Cu₇O_y (247 phase) was examined at 1 atm of oxygen partial pressure under the following conditions; (l)using NaNO₃ as a reaction accelerator, (2)without reaction accelerator and without seed and (3)using the seeding method, respectively. They were pressed and fired at 850–900°C under oxygen gas flow. The 247 phase was obtained in the temperature range from 860°C to 890°C using NaNO₃. Under the condition(2), however, the 247 phase could not be formed in the same temperature range. But, the seeding method was effective; the 247 phase formed at the temperature range from 870°C to 890°C. The sample of the 247 phase prepared at 870°C under the condition(1) exhibited superconductivity with zero resistive point at 93 K.