Phase stability of $La0.5Sr0.5CoO3−y$ films upon annealing in hydrogen atmosphere

The effect of annealing epitaxial $La0.5Sr0.5CoO3−y$ films in forming gas (FG) mixed with 0.01%, 0.1%, and $1%mol$ oxygen was investigated using in situ x-ray diffraction at temperatures up to $800°C$⁠. The phase transition that occurs at $275°C$ in pure FG is shifted to higher temperatures by small admixtures of oxygen in FG. Electron diffraction patterns demonstrate that this is a transition into an oxygen-deficient ordered phase with $0,1∕3,0$ and $0,2∕3,0$ superstructures. The $La0.5Sr0.5CoO3−y$ phase can be recovered by annealing in oxygen at moderate temperatures as long as it has not decomposed at higher temperatures.