Manipulation of Optical Transmittance by Ordered-Oxygen-Vacancy in Epitaxial LaBaCo₂O_5.5+δ Thin Films

Giant optical transmittance changes of over 300% in wide wavelength range from 500 nm to 2500 nm were observed in LaBaCo₂O_5.5+δ thin films annealed in air and ethanol ambient, respectively. The reduction process induces high density of ordered oxygen vacancies and the formation of LaBaCo₂O_5.5 (δ = 0) structure evidenced by aberration-corrected transmission electron microscopy. Moreover, the first-principles calculations reveal the origin and mechanism of optical transmittance enhancement in LaBaCo₂O_5.5 (δ = 0), which exhibits quite different energy band structure compared to that of LaBaCo₂O₆ (δ = 0.5). The discrepancy of energy band structure was thought to be the direct reason for the enhancement of optical transmission in reducing ambient. Hence, LaBaCo₂O_5.5+δ thin films show great prospect for applications on optical gas sensors in reducing/oxidizing atmosphere.