Topotactic transition between perovskite and brownmillerite phases for epitaxial LaCoO3-delta films and effects thus resulted

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 LaCoO3-delta (delta = 0-0.5) epitaxial film by annealing the sample under different conditions. In the atmosphere of 2 x 10(-4) Pa, LaCoO3 film is transformed from the perovskite structure to the brownmillerite structure when annealing temperature exceeds 500 degrees 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 rho-T-1/4 curve, without affecting the ln rho-T-1/4 slope. We found signatures for preferential distribution for oxygen vacancies; the latter prefer to appear near high spin Co3+ ions in the initial stage when they are introduced into the lattice, resulting in abnormal magnetic and transport behaviors.