Epitaxial nature and transport properties in (LaBa)Co₂O _5+δ thin films

Epitaxial (LaBa)Co2O_5+δ thin films were grown on (001) LaAlO₃ single-crystal substrates using pulsed laser deposition. Microstructure characterizations from X-ray diffraction and electron microscopy indicate that the films are highly c-axis oriented with cube-on-cube epitaxy. Transport property measurements indicate that the films have typical semiconductor behavior with a novel phase transition and hysteresis phenomena at 540 K. The chemical dynamic studies reveals that the resistance of the film changes drastically with the change of redox environment, i.e., the magnitude of resistance changes, ΔR = 1 × 10²↔1 × 10 ⁶, is found within a short response time (∼700ms). These phenomena suggest that the as-grown (LaBa)Co₂O_5+δ film have extraordinary sensitivity to rcducing-oxidizing environment and the exceedingly fast surface exchange rate.