Ti-Doped AgNbO₃ as Novel Dense Diffusion Barriers of Limiting Current Oxygen Sensors

The oxygen sensors with limiting current derived from a dense diffusion barrier have an excellent advantage of detecting oxygen partial pressure by controlling the ratio of air and fuel in combustion environments. Therefore, AgNb_1-TiO_3-δ (wherein x varies from 0.1 to 0.3) was prepared as such a dense diffusion barrier layer for sensor application. Among the investigated compositions as a new condensed barrier for the diffusion of sensors, AgNb_1-TiO_3-δ (x = 0.1, 0.2, 0.3) exhibits oxygen ionic conductivities from 1.37 × 10^-4 to 5.78 × 10^-3 S·cm^-1 in the temperature range of 600-900 °C and outstanding stable electrochemical properties. Herein, we employ these novel materials as dense diffusion barriers and 8 mol % zirconia stabilized by yttria (8YSZ) as a solid-state electrolyte for the fabrication of the oxygen sensors with limiting current. We observed a direct connection between the limiting current and oxygen content within the interval of 0.5-5.0 mol % at 800 °C and a low working voltage. The increase of Ti-doping amount in AgNbO₃ accelerates the sensing response to oxygen gas and promotes the service life of the sensor.