Topotactic Phase Transition in Epitaxial La_0.7Sr_0.3MnO_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_0.7Sr_0.3MnO_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_0.7Sr_0.3MnO_3-δ thin films grown via physical vapor deposition. The efficiency of this method is confirmed using La_0.7Sr_0.3MnO_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.