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Controlling oxygen redox reactions in transition metal oxides offers an attractive route to tune their physical properties; a topotactic structural transformation from their parent phases effectively modifies the electronic state. In this work, infinite-layered SrFeO2 thin films were produced from brownmillerite SrFeO2.5 via low-temperature hydro-reduction. After the structural transition, their out-of-plane lattice constants dramatically shrank by ∼12%; tensilely strained samples exhibited metallic character, whereas the compressively strained ones maintained the insulating behavior of their bulk form. According to X-ray linear dichroism results, this strain-mediated electronic anisotropy may be attributed to electron redistribution within degenerated orbitals. This suggests a possible mechanism for the metallic conductivity of infinite-layered SrFeO2, giving a hint for understanding emergent quantum phenomena, such as the recently discovered superconductivity in nickelates, and stimulating various applications, including in ionic conductivity and oxygen catalysis.

As an alternative electrode material, transition metal oxides are promising candidates due to multivalent nature and oxygen vacancies present in the structure with facilitate redox reactions. The aim of this study is to explore the intrinsic mechanism of oxygen evolution reaction (OER) using two-dimensional thin film La1− x Sr x CoO3 electrode as a model. Herein, we report a planar two-dimensional model La1− x Sr x CoO3 electrode grown on a Nb-SrTiO3 single-crystal substrate via pulsed laser deposition. The two-dimensional La1− x Sr x CoO3 films offer different oxygen evolution activities at different pH electrolyte solutions. The mechanisms behind the variations of the oxygen evolution activity were discussed after comparing the oxygen evolution activity before and after treatments of the electrodes and measurements by various test methods. The results of this study offer a promising, low-cost electrode material for the efficient OER and a sustainable production of hydrogen fuel.

BiFeO 3 (BFO) thin films with BaTiO 3 (BTO) or SrTiO 3 (STO) as buffer layer were epitaxially grown on SrRuO 3 -covered SrTiO 3 substrates. X-ray diffraction measurements show that the BTO buffer causes tensile strain in the BFO films, whereas the STO buffer causes compressive strain. Different ferroelectric domain structures caused by these two strain statuses are revealed by piezoelectric force microscopy. Electrical and magnetical measurements show that the tensile-strained BFO/BTO samples have reduced leakage current and large ferroelectric polarization and magnetization, compared with compressively strained BFO/STO. These results demonstrate that the electrical and magnetical properties of BFO thin films can be artificially modified by using a buffer layer.

We investigated the effects of oxygen vacancies on the structural, magnetic, and transport properties of La1– x Sr x MnO3 ( x =0.1, 0.2, 0.33, 0.4, and 0.5) grown around a critical point (without/with oxygen vacancies) under low oxygen pressure (10 Pa) and high oxygen pressure (40 Pa). We found that all films exhibit ferromagnetic behavior below the magnetic critical temperature, and that the films grown under low oxygen pressures have degraded magnetic properties with lower Curie temperatures and smaller magnetic moments. These results show that in epitaxial La1– x Sr x MnO3 thin films, the magnetic and transport properties are very sensitive to doping concentration and oxygen vacancies. Phase diagrams of the films based on the doping concentration and oxygen vacancies were plotted and discussed.

The ultrafast laser-excited magnetization dynamics of ferromagnetic (FM) La0.67Sr0.33MnO3 (LSMO) thin films with BiFeO3 (BFO) coating layers grown by laser molecular beam epitaxy are investigated using the optical pump-probe technique. Uniform magnetization precessions are observed in the films under an applied external magnetic field by measuring the time-resolved magneto-optical Kerr effect. The magnetization precession frequencies of the LSMO thin films with the BFO coating layers are lower than those of uncoated LSMO films, which is attributed to the suppression of the anisotropy field induced by the exchange interaction at the interface between the antiferromagnetic order of BFO and the FM order of LSMO.