Abstract
Hot-spots appearing on several RE123 ceramics upon application of external voltage have been reported to show sensitivity towards different oxygen partial pressures. In this paper, influence of hot-spot temperature in the range of 160–810 °C on oxygen sensing behavior of Er123 sensor rods is reported. Simultaneous measurements of hot-spot temperature and output current response in different oxygen partial pressures between 1% and 100% showed hot-spots operating at temperatures as low as 660 °C in 1% oxygen partial pressure produced good stability and repeatability. Response time for oxygen sensing was observed to decrease with increasing hot-spot temperature, with minimum value of 0.50 s recorded at 695 °C in 1% oxygen partial pressure. In addition, a large change in activation energy from 2.8 eV to 0.626 eV was established at around 670 °C and this has been suggested to be related to structural change from orthorhombic to tetragonal taking place at around the same temperature. The reduction of activation energy increased diffusion of oxygen ions in the rod and caused rapid changes in resistivity which triggered movement of the hot spot to the negative electrode.
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