At what temperature do oxygen ions become mobile in doped zirconia?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

conductive ceramics Figure 1: Schematic diagram of a zirconia oxygen sensor used to monitor automobile exhaust gases. The sensor, approximately the size of a spark plug, is fitted into the exhaust manifold of an automobile engine. The thimble-shaped zirconia sensor, sandwiched between thin layers of porous platinum, is exposed on its interior to outside air and on its exterior to exhaust gas passing through slits in the sensor shield. The two platinum surfaces serve as electrodes, conducting a voltage across the zirconia that varies according to the difference in oxygen content between the exhaust gas and the outside air.

In doped zirconia, oxygen ions ( $O^{2 -}$ ) become mobile at temperatures above 600°C (1,100°F).1

When zirconia is doped with ions such as $C a^{2 +}$ or $Y^{3 +}$ , oxygen vacancies are created within the material's structure. Once the temperature exceeds the 600°C threshold, oxygen ions gain sufficient mobility to move through and fill these vacancies, a process that facilitates ionic conduction. Because this threshold must be met for the material to conduct effectively, zirconia heating elements require a preheater to reach the necessary operating temperature.1