Oxidation of Ba2YCu3Ox at High Po2

Dense large‐grain ceramic samples of Ba2YCu2Ox have been oxidized at 400° to 500°C in 10 to 30 MPa of oxygen for 1 to 10 d. The high‐pressure treatment has increased the equilibrium content x slightly above 7 but there is no concomitant increase in Tc. At x = 7.03 the superconducting transition, measured by ac susceptibility, has an onset temperature of ∼91 K and ΔT∼4 K and no change in lattice parameter is observed. High oxygen pressure increases the rate of oxidation.