# Nature and stability of the "60-K superconducting phase" in the $YBa_2Cu_3O_7-\delta$ system

Rao, CNR and Nagarajan, R and Ganguli, AK and Subbanna, GN and Bhat, SV (1990) Nature and stability of the "60-K superconducting phase" in the $YBa_2Cu_3O_7-\delta$ system. In: Physical Review B, 42 (10). 6765 - 6768.

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Official URL: http://prb.aps.org/abstract/PRB/v42/i10/p6765_1

## Abstract

Based on electron microscopy, nonresonant microwave absorption, electron paramagnetic resonance, and other studies, it is shown that in the $YBa_2Cu_3O_7-\delta$ system, compositions with $\delta = 0.0-0.20$, 0.25, and 0.5 are stable and monophasic, the last two being associated with ordered-oxygen-vacancy structures. The $\delta = 0.3-0.4$ region $(T_c \sim 60 K)$ is not associated with an ordered-vacancy structure. More importantly, compositions in this region undergo structural changes on annealing at relatively low tempertures, eventually decomposing to the more stable phases. It appears that compositions such as $YBa_2Cu_3O_{6.7}$ are not thermodynamically stable, casting thereby some doubt on the belief that the 60-K regime represents a genuine single-phase superconducting material.

Item Type: Journal Article Copyright of this article belongs to American Physical Society. Division of Chemical Sciences > Solid State & Structural Chemistry Unit 12 Jul 2007 25 Jan 2012 08:45 http://eprints.iisc.ernet.in/id/eprint/11531