Thermogravimetric study of the La/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-//sub delta/ system: The correlation of T/sub c/ with oxygen content

We report a systematic study of a series of single-phased La/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-//sub delta/ samples where the oxygen content was determined by thermogravimetric analysis. The highest zero-resistance T/sub c/ was 72 K, corresponding to delta = 0.25. An increase in delta reduced T/sub c/ to 44 K, similar to the behavior reported for Y/sub 1/B/sub 2/Cu/sub 3/O/sub 7-//sub delta/. This is consistent with the idea that as oxygen is taken away from the planes where Cu-O chains exist, T/sub c/ is reduced. For samples where the oxygen content was increased until $delta: became negative, T/sub c/ decreased to a value as low as 23 K, presumably due to increased La-Ba disorder. These samples with low T/sub c/ and high oxygen content have apparent tetragonal x-ray spectra, suggesting that Cu-O chain ordering has been further disrupted and that the oxygen occupancy on these planes has increased.