Oxygen Stoichiometry and Ag Substitution in Pb sub 2 Sr sub 2 Y sub (1-x) Ca sub x Cu sub (3-y) Ag sub y O sub (8+delta)

Thermogravimetry and x-ray powder diffraction have been used to study the oxygen stoichiometry in Pb sub 2 Sr sub 2 YCu sub 3 O sub (8+delta) and compositions with Ca substituted for Y and Ag for Cu as a function of temperature and p sub O sub 2. Reversible addition of oxygen occurs at 300-600C to a maximum of delta=1.6 at 540C in 1 atm. oxygen. Irreversible oxygen uptake accompanied by decomposition into Pb sup (4+) containing perovskites occurs around 700C. These perovskites lose oxygen and revert to the parent phase above 850degrees in air. This behavior allows preparation of the phase at high temperatures in air provided they are quenched to avoid reoxidation on cooling.