α-Iron oxide: An intrinsically semiconducting oxide material for direct thermoelectric oxygen sensors

Intrinsically semiconducting oxide materials offer the possibility for highly sensitive direct thermoelectric gas sensors. Intrinsic alpha-Fe2O3 has been chosen as a well suited candidate for direct thermoelectric gas sensors. The band gap of alpha-Fe2O3 is relatively low for an oxide material (2.2 eV). The intrinsic behavior is present for temperatures above 400 degrees C. The tested direct thermoelectric oxygen sensors were actively heated to the operating temperature at 580 degrees C. The achieved sensitivity (85 mu V K-1 per decade oxygen partial pressure) is about 3 times higher compared to typical conductometric oxygen sensitive materials like SrTiO3/SrTi1-xFexO3-delta. The used temperature modulation technique combined with a regression analysis allowed a determination of the measurand thermopower within 6.4s and the possibility for self-diagnostics. These presented results show a possible realization of fast, accurate, highly sensitive direct thermoelectric gas sensors. (C) 2010 Elsevier B.V. All rights reserved.