Anomaly Negative Resistance Phenomena in Highly Epitaxial PrBa0.7Ca0.3Co2O5+δ Thin Films Induced from Superfast Redox Reactions
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Thin films of Ca-doped double perovskite, PrBa<sub>0.7</sub>Ca<sub>0.3</sub>Co<sub>2</sub>O<sub>5+δ</sub> (PBCC), were epitaxially grown on (001) SrTiO<sub>3</sub>, and their redox reactions under a switching flow of H<sub>2</sub> and O<sub>2</sub> gases were examined at various temperatures by measuring the resistance R(t) of the films as a function of the gas flow time t. In the temperature range between 350 and 725 °C, these thin films are reduced and oxidized in an ultrafast manner under the flow of H<sub>2</sub> and O<sub>2</sub> gases, respectively, suggesting that PBCC thin films are promising candidates for developing ultra-sensitive oxygen sensors or SOFC cathodes at intermediate or high temperatures. When the gas flow is switched to O<sub>2</sub>, the reduced PBCC thin films exhibit a negative resistance at temperatures above 600 °C but a positive resistance at temperatures below 600 °C. The probable cause for these anomalous transport properties is the diffusion of the H atoms from the cathode to the anode in the PBCC film, which provides a current opposite to that resulting from the external voltage.
Physics and Astronomy