Abstract
Giant optical transmittance changes of over 300% in wide wavelength range from 500 nm to 2500 nm were observed in LaBaCo2O5.5+δ thin films annealed in air and ethanol ambient, respectively. The reduction process induces high density of ordered oxygen vacancies and the formation of LaBaCo2O5.5 (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 LaBaCo2O5.5 (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, LaBaCo2O5.5+δ thin films show great prospect for applications on optical gas sensors in reducing/oxidizing atmosphere.
Highlights
Perovskite cobaltites have been paid considerable attention of research in the past two decades due to their unique physical properties, such as magnetic, electronic and optical properties, which resulting from the strong correlation and interactions of charge, orbital, spin and photon[1,2,3,4,5,6,7]
The epitaxial LBCO thin films exhibit several impressing improvement of physical properties, for example, a much larger magnetoresistance value was observed on epitaxial thin films than those from its bulk material at low temperatures; besides, LBCO thin films possess extraordinary sensitivity to reducing/oxidizing environments, especially an exceedingly fast redox reaction at high temperature[17,18,19,20,21,22,23,24,25,26,27,28]
We find out that the LBCO optical gas sensors can be used to detect the ethanol gas by the transmittance changes of the LBCO films between Air and ethanol vapor gas with obviously high optical sensitivity
Summary
Transmittance by Ordered-Oxygenreceived: 18 May 2016 accepted: 26 October 2016 Published: 23 November 2016. The remarkable mixed conductivity and catalytic properties at high temperature and exciting magnetic and electrical transport properties at low temperature have been intensively studied by scientists and technicians[8,9] All these excellent physical properties have encouraged people to design lots of kinds of functional devices, including solid oxide fuel cells, energy harvest devices, electrical and chemical sensors, etc[10,11,12,13]. The LBCO films exhibited good gas sensing properties at a fairly low temperature of 375 °C, which have the potential for the development of the electronic gas sensor devices by using the resistance switching[13]. The ordered oxygen vacancies in LBCO films have been directly measured and the mechanism of optical transmittance enhancement induced by ordered oxygen vacancies has been explored
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