Nature and stability of the ‘‘60-K superconducting phase’’ in the YBa2Cu3O7−δ system
C. N. R. Rao, R. Nagarajan, A. K. Ganguli, G. N. Subbanna, S. V. Bhat
DOI 10.1103/PhysRevB.42.6765 · Physical Review B
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Abstract
Based on electron microscopy, nonresonant microwave absorption, electron paramagnetic resonance, and other studies, it is shown that in the YBa2Cu3O7−δ system, compositions with δ=0.0– 0.20, 0.25, and 0.5 are stable and monophasic, the last two being associated with ordered-oxygen-vacancy structures. The δ=0.3–0.4 region (Tc∼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 YBa2Cu3O6.7 are not thermodynamically stable, casting thereby some doubt on the belief that the 60-K regime represents a genuine single-phase superconducting material.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| YBa2Cu3O7-δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 90 | Pressure not reported | unknown |
| YBa2Cu3O6.75 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 77 | Pressure not reported | unknown |
| YBa2Cu3O6.7 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 60 | Pressure not reported | unknown |
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