ND(1-X)CU3O(Y) PROCESSED IN HIGH-PRESSURE OXYGEN - EFFECTS OF ENHANCED OXYGEN-UPTAKE ON STRUCTURE AND SUPERCONDUCTIVITY(X)BA(2)

The T(c) of Nd1+xBa2-xCu3Oy (0.1 less-than-or-equal-to x less-than-or- equal-to 0.6) has been increased by synthesizing and annealing the com pounds in 200 bar oxygen pressure. The oxygen content, y, increases to compensate the effect of Nd'' substitution and the formal average cop per valence (FACV) remains unchanged at approximately 2.3 throughout t he composition range. Although the FACV remains constant, T(c) falls s ystematically with increasing x, suggesting that Nd3+ at the Ba2+ site binds a portion of holes. Thermogravimetric data show an increasingly negative slope of the weight-temperature plot with larger x, indicati ng that the enthalpy for binding the oxygen in the CuO chain increases when oxygen per formula unit increases beyond seven.