Topotactic Phase Transition in Epitaxial La 0.7 Sr 0.3 MnO 3‐δ Films Induced by Oxygen Getter Assisted Thermal Annealing

Oxygen vacancies play a crucial role in controlling the physical properties of complex oxides. In La 0.7 Sr 0.3 MnO 3‐δ , the topotactic phase transition from Perovskite (PV) to Brownmillerite (BM) can be triggered, e.g., via oxygen removal during thermal annealing. Here, a very efficient thermal vacuum annealing method is reported using aluminum as an oxygen getter material. The topotactic phase transition is characterized by X‐ray Diffraction, which confirms a successful transition from PV to BM in La 0.7 Sr 0.3 MnO 3‐δ thin films grown via physical vapor deposition. The efficiency of this method is confirmed using La 0.7 Sr 0.3 MnO 3‐δ micron‐sized bulk powder. The accompanying transition from the original Ferromagnetic (FM) to an Antiferromagnetic (AF) state and the simultaneous transition from a metallic to an insulating state are characterized using Superconducting Quantum Interference Device (SQUID) magnetometry and Alternating Current (AC) resistivity measurements, respectively. The near‐surface manganese oxidation states are probed by synchrotron X‐ray Absorption Spectroscopy. Moreover, X‐ray Reflectivity, Atomic Force Microscopy, and Scanning Transmission Electron Microscopy reveal surface segregation and cation redistribution during the oxygen getter‐assisted annealing process.