OXYGEN DEFICIENCY OF Ba2YCu3O7 - delta AND SUPERCONDUCTIVITY.

Oxygen deficiency of Ba//2YCu//3O//7// minus // delta was studied by thermogravimetry and thermodilatometry. Ba//2YCu//3O//7// minus // delta rapidly releases and adsorbs oxygen at a temperature in the vicinity of 150 degree C. delta was controlled by cooling the specimen in O//2 gas flow after annealing in an Ar gas atmosphere (O//2/Ar annealing) and by Ar/O//2 annealing. The lattice constants a and b in the O//2/Ar annealed specimen show an almost constant value in the range O less than delta less than 0. 7 while (a-b) in the Ar/O//2 annealed specimen decreases with delta . The Tc of the Ar/O//2 annealed sample differs from that of O//2/Ar annealed sample even if the samples have the same value of delta .