Annealing in vacuum at above 600K introduced O vacancies into the RuO2, and possibly the CuO2, planes. Diffusive jumps of the O vacancies were accompanied by a reorientation of the local distortion, and were probed by measuring the elastic energy loss and modulus as a function of temperature at 1 to 10kHz. An intense acoustic absorption peak developed near to 670K at 1kHz, and finally stabilized after heating at up to 920K under vacuum. An analysis of the peak indicated a barrier, to O diffusion, of about 1.4eV and a slowing down of Curie-Weiss type (with TC = 400 to 470K) due to interactions among the O vacancies. A secondary peak was attributed to O vacancies which were trapped at defects in the RuO2 planes, or to vacancies in the CuO2 planes.

Formation and Mobility of Oxygen Vacancies in RuSr2GdCu2O8. F.Cordero, M.Ferretti, M.R.Cimberle, R.Masini: Physical Review B, 2003, 67[14], 144519 (7pp)