Topotactic transition between perovskite and brownmillerite phases for epitaxial LaCoO <sub> 3− <i>δ</i> </sub> films and effects thus resulted
Hailin Huang, Jine Zhang, Ji Ma, Furong Han, Xiaobing Chen, Jinghua Song, Jing Zhang, Shaojin Qi, Yuansha Chen, Jianwang Cai, Fengxia Hu, Baogen Shen, Jirong Sun
Abstract
Abstract Oxygen vacancy distribution has a direct effect on the crystal structure and physical properties of complex oxides, resulting in versatile applications. Here, we report on a reversible topotactic phase transition between the perovskite and brownmillerite structures for the LaCoO 3− δ ( δ = 0–0.5) epitaxial film by annealing the sample under different conditions. In the atmosphere of 2 × 10 −4 Pa, LaCoO 3 film is transformed from the perovskite structure to the brownmillerite structure when annealing temperature exceeds 500 °C. Meanwhile, the magnetic order transits from ferromagnetic to anti-ferromagnetic. Variable-range hopping demonstrates the electronic transport process for both phases. The incorporation of oxygen vacancies results in an upward shift of the ln ρ - T −1/4 curve, without affecting the ln ρ - T −1/4 slope. We found signatures for preferential distribution for oxygen vacancies; the latter prefer to appear near high spin Co 3+ ions in the initial stage when they are introduced into the lattice, resulting in abnormal magnetic and transport behaviors.