Material problems of oxide superconductors from chemical aspects

Chemically unique properties of Ba/sub 2/LnCu/sub 3/O/sub y/ (Ln=rare earth element) superconductors raise various problems. Firstly, apparent resistivity anomalies are observed when the specimen surface acquired humidity. This phenomenon turned out to be the electrochemical effect that the suprious electromotive force appears at the electrode, indicating the importance of careful resistivity measurements. Secondly, oxygen content y significantly vary from 6.0 to 6.93, slightly depending in Ln ion. However, it does not increase any more even by the high pressure treatment in oxygen up to 50 atm. Thirdly, although the low temperature annealing is generally accepted to be effective in bringing out good superconducting properties, electrical resistivity deteriorates after a prolonged heat treatment at 200-3000C. The creation of highly resistive layer at the rain boundary is assumed to be responsible for the above effect