HIGH-TEMPERATURE THERMODYNAMICS OF OXYGEN EQUILIBRIUM OF SOLID-SOLUTIONS YBA2CU3-XZNXO6-PHASE(DELTA WITH GAS)

The equilibrium oxygen content was measured in the solid solution YBa2 Cu3xZnxO6-delta, where x=0, 0.1, 0.2, 0.3, in the temperature range 60 0-825 degrees C and oxygen pressure between 10(-5) and 1.0 atm. The co ncentration dependencies of the partial molar enthalpy Delta H degrees (delta) and entropy Delta S degrees(delta) of oxygen were determined. A decrease of both Delta H degrees(delta) and Delta S degrees(6) at de lta <0.2 is observed. This behavior is interpreted as evidence that pa rticipation of the apex O4 oxygen in the gas<->solid equilibrium occur s with exhaustion of the O1 and O5 oxygen positions in the basal plane . (C) 1998 Elsevier Science S.A.