Ex situ studies of the surface passivation effect due to oxidizing pre-annealing show that the delayed exsolution is directly correlated to a reduced particle volume as determined by microscopic investigations. The sample pieces were pre-annealed under oxidizing conditions for t = 20 min, t = 60 min and t = 180 min (p(O2) = 0.108 mbar, T = 400 C) and compared to an as-prepared sample and a sample with an intentional SrO termination layer after thermal reduction in the same process step (4% H2/Ar, 400 C, t = 5 h). Dashed lines serve as guides for the eye. Sample conditions are denoted by the colour code (blue, yellow and grey shading) at the top of a.
