Manipulation of Optical Transmittance by Ordered-Oxygen-Vacancy in Epitaxial LaBaCo2O5.5+δ Thin Films

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.

Ordering and Phase Control in Epitaxial Double-Perovskite Catalysts for the Oxygen Evolution Reaction

“…Due to the low oxidation state of Co cations, cobaltites contain a particularly large concentration of oxygen vacancies, potentially yielding oxygen nonstoichiometry of several tens of percent (i.e., δ may take values up to 0.8, while maintaining cubic symmetry of the lattice). As a result, oxygen vacancies can show coherent ordering rather than statistical distribution within the lattice. ,, In this case, oxygen vacancies are found to be located in various compounds within every other CoO 2−δ atomic plane − (in the PBCO case referred to as (Pr 0.5 Ba 0.5 ) 2 Co 2 O 5+δ ; Figure c), which in the extreme case may lead to the formation of a brownmillerite structure such as that reported for SrCoO 2.5 − ).…”

“…In-plane strained (0,1,3) PBCO peaks are observed in all films, while a (0,1,5/2) peak appears only for samples grown at high temperature. contradicts some literature reports on PBCO powders (typically treated at temperatures above 1000 °C) 30,49 but is consistent with reports on SrCoO 3−δ thin films, 56 (La,Ba)-CoO 3−δ , 32 (Y,Sr)CoO 3−δ , 53 and (La,Sr)MnO 3−δ . 54,55 Limited kinetics during thin film growth and epitaxial strain (which is absent in powders) may explain these differences.…”

“…As a result, oxygen vacancies can show coherent ordering rather than statistical distribution within the lattice. 18,32,52 In this case, oxygen vacancies are found to be located in various compounds within every other CoO 2−δ atomic plane 53−55 (in the PBCO case referred to as (Pr 0.5 Ba 0.5 ) 2 Co 2 O 5+δ ; Figure 1c), which in the extreme case may lead to the formation of a brownmillerite structure such as that reported for SrCoO 2.5 56−58 ). Mixed A-site cobaltites, such as PBCO, may however exhibit even more complex atomic configurations; this is an ordered double-perovskite structure, in which the A-site cations order coherently as well (see e.g.…”

“…24,30,31 At elevated temperatures, fast oxygen exchange kinetics have been reported for PBCO 36,59 leading to considerable efforts to use PBCO in solid oxide fuel cells 60 and oxygen sensors. 32 Given the complex atomic structure of mixed A-site cobaltites, however, the validation of structure− property relations frequently being used in rational design rules for catalysts requires careful processing and a detailed analysis. Judgment of electrocatalytic performance should be accompanied by careful determination of the atomic structure of the catalyst, in order to derive a relation between materials chemistry and electrocatalytic performance.…”

“…In addition to noble metals and binary metal oxides such as IrO 2 or RuO 2 , ,− (double) perovskites have been studied as active materials for the OER ,,,− as well as for fuel cell applications in recent years. This is (1) because of the wide variety of available compositions and stoichiometry in this class of materials and (2) because of their specific surface structure which provides potentially active sites for adsorption of reactants ,, and promotes oxygen exchange between active electrode and electrolyte .…”