Influence of Water Treatment of LaF3 Crystal on LaF3-Based Oxygen Sensor Workable at Room Temperature

Abstract
The effects of a water treatment of the LaF3 single crystal on an LaF3-based oxygen sensor were investigated. It was found that the oxygen-sensing properties were significantly affected by the water treatment depending on the perovskite-type oxides (LaCrO3, LaCoO3, La0.8Ca0.2MnO3) used as the sensing electrode material and the duration of the treatment. As revealed by XPS, the treatment induced the incorporation of oxygen in the surface region of the LaF3 crystal, leading to an increase in the number of electrons of the electrochemical reduction of oxygen from 1 or 2 to 4.