Aim of this proposal is to determine the crystal structure of a series of oxygen-deficient LSF specimen to understand the role of oxygen and Fe deficiencies in their structural and physicochemical properties. We showed that iron exsolution occurs in reductive environments at higher temperatures, leading to the formation of Fe rods on the surface. Utilizing an array of complementary in situ and ex situ techniques we currently characterize this phenomenon regarding its thermodynamic and kinetic properties: subsequently to the Fe exsolution, the perovskite exhibits a nonlinear shift of the diffraction peaks to smaller 2theta which can be attributed to a rhombohedral (R-3c) to cubic (Pm-3m) structural transition. In reducing atmospheres the cubic structure is stabilized to room temperature whereas the transition is reversible in oxidizing conditions. O and Fe deficiencies (to be determined by HR neutron diffraction) are expected to play a crucial role in stabilizing the cubic structure.