Perovskite-type oxides of BaxSr1 - xFeP3 (x = 0, 0.1, 0.5, 0.9 and 1.0) were examined as a sensing electrode (SE) material of potentiometric yttria-stabilized zirconia (YSZ)-based oxygen sensors. The sensors using each of BaxSr1 (-) xFeO3-SEs were found to be insensitive to the various examined gases (100 ppm each) such as NH3, H-2, C3H6, C3H8, CH4, NO2, NO and CO, while they were sensitive to oxygen in the concentration range of 0.05-21 vol.% at 600 degrees C. The number of electron (n) in the electrochemical reaction of oxygen for the present sensors was estimated to be about 42 based on Nernst equation in the examined concentration range. The estimated n values for the present sensors are consistent with that (n = 4.2) for the conventional YSZ-based oxygen sensor using Pt-SE, being almost same as the theoretical value (n = 4). The YSZ-based sensor attached with BaFeO3-SE further showed excellent responses at temperatures of 450-600 degrees C. The electric potential difference (AV) value of the present sensor was rather stable under the operating conditions (relative humidity: 20-100%, 400 ppm CO2, 600 degrees C) for the examined period of 14 days. In addition, it was found that the sensor using BaFeO3-SE could work well as a lambda (lambda) sensor at 600 degrees C in the combustion gas of O-2/C3H8, as is the case with the sensor using Pt-SE. (C) 2015 Elsevier B.V. All rights reserved.