Abstract
Direct conversion of superconducting Y 2 Ba 4 Cu 7 O 15-δ (Y-247) from YBa 2 Cu 3 O 7-x (Y-123) was achieved at atmospheric pressure. The Y-247 samples were synthesized by the reactions of Y-123 and Cu-(NO 3 ) 2 at 860°C in an O 2 ambient. The results strongly suggest that Y-247 is a thermodynamically more stable phase than Y-123 at the atmospheric pressure. The conversion also provides a novel and simple route to synthesize the Y-247 compound.