Carbon dioxide gas sensing properties of ordered oxygen deficient perovskite LnBaCo2O5+δ (Ln=La, Eu)

Polycrystalline samples of layered cobaltites LnBaCo2O5+δ (Ln=La, Eu) were synthesized by standard solid state reaction. Structural, magnetic and carbon dioxide gas sensing properties of the samples were carefully investigated. The polycrystalline LnBaCo2O5+δ samples showed typical sequences of magnetic transitions according to the nonstoichiometric oxygen (δ) content. Well-defined hysteresis loops were observed at different temperatures (270K for EuBaCo2O5+δ), which supports the existence of a ferromagnetic order in the samples. Thick films were prepared with the as-prepared powders for the gas sensing evaluation. Considerable response to CO2 gas was measured for the first time on sensors based on LnBaCo2O5+δ powders. The resistance of the sensors increases with an increase of CO2 concentration, with dry air as base gas. The gas sensing response of the sensors is fast and shows good reproducibility. The EuBaCo2O5+δ, and LaBaCo2O5+δ cobaltites show distinct behavior upon increase in the CO2 concentration, which might be associated with the value of δ for each system. The probable carbon dioxide gas sensing mechanism of the studied cobaltites is discussed.