Abstract
The authors have reversibly oxygenated and deoxygenated in situ-formed thin films of YBa/sub 2/Cu/sub 3/O/sub x/ by means of low-temperature anneals in oxygen and argon. The transition shape for slightly deoxygenated material is consistent with the existence of two superconducting phases, which may be distinguished by different oxygen ordering. The authors investigated J/sub c/(B) as a function of oxygen content in samples whose oxygen content has been controlled by low-temperature anneals. The steep rise in J/sub c/ with T/sub c/. has been demonstrated and the effect on J/sub c/ of change in c investigated. It is confirmed that in situ-formed films which have low T/sub c/ as-deposited have anomalously high c values, but it is demonstrated that good films (that is, films which as deposited have c approximately 1.168 nm and T/sub c/ approximately 90 K) follow the bulk c vs. T/sub c/ relationship when deoxygenated and reoxygenated in low-temperature anneals. The cause of the c expansion is attributed to a defect, possibly the substitution of Ba for Y, introduced at the time of film deposition under conditions of low mobility. Some data have been obtained which suggest that films deposited on substrates at higher temperatures have c vs. T/sub c/ more consistent with bulk data.
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