An investigation was made of the absorption of interstitial O and of the formation of O vacancies in samples which were in equilibrium with O partial pressures of between 10-4 and 103Torr, or in a vacuum, at high temperatures. Below 600C, the vacancy concentration was negligible and the equilibrium between the sample and gaseous O involved only interstitial O. The pressure versus composition equilibrium curve was determined, at 550C, by repeated vacuum extraction from a fixed volume. An analysis of the partial desorption stages indicated the formation of interstitial O2- ions; with corrections due to the formation of peroxide species, such as pairs of O ions with an ionization number of -2 or -3 instead of -4. Equilibrium fractions of O vacancies of up to 8% could be created above 720C at pressures below 0.1Torr. These were reversibly filled by re-oxygenation at high temperatures, without decomposition of the sample. The vacancies were much less mobile than interstitial O, and were in the CuO2 plane. They could be frozen-in, and coexisted with interstitial O.

Interstitial O and O Vacancies in La2CuO4 during High-Temperature Treatments. F.Cordero, R.Cantelli: Physica C, 1999, 312[3-4], 213-24