1.3.1 Suppression of the NO2 interference by Chromium Addition in WO3-Based Ammonia Sensors. Investigation of the Structural Properties and of the Related Sensing Pathways

14th International Meeting on Chemical Sensors - IMCS 2012
2012-05-20 - 2012-05-23
Nürnberg/Nuremberg, Germany
1.3 Metal Oxide-based Gas Sensors I
M. Epifani, P. Siciliano - Consiglio Nazionale delle Ricerche – Istituto per la Microeletronica ed I Microsistemi (CNR -IMM) (Italy), T. Andreu, J. Morante - Catalonia Institute for Energy Research (Spain), J. Arbiol - Institut de Ciència de Materials de Barcelona, ICMAB-CSIC (Spain), N. Garcia-Castello, J. Prades - Albert Cirera, Departament d’Electrònica, Universitat de Barcelona (Spain)
96 - 99


WO3 and Cr-WO3 powders were prepared by sol-gel process, with Cr:W atomic concentration ranging from 2% to 8.8%. WCl6 was used as W precursor and reacted with methanol in presence of acetyacetone as stabilizer. The required amount of Cr 2-ethylhexanoate was then added to the resulting solution, which was then dried. The resulting powder was heat-treated at temperatures ranging from 200 to 700 °C. With increasing the Cr concentration, the samples heat-treated at 500 °C contained an increasing amount of the additional phase Cr2WO6. The analysis of the X-ray diffraction and Transmission Electron Microscopy data showed that the use of the Cr 2-ethylhexanoate precursor seemed to favor Cr incorporation in interstitial position in the WO3 lattice. The sensing tests towards ammonia gas, from 50 to 500 ppm, showed that, up to 5% concentration, Cr addition lowered the best operating temperatures and/or enhanced the response with respect to pure WO3, then the response remarkably decayed. Detailed structural and electrical investigation showed that interstitial Cr controlled the concentration of the oxygen vacancies. The decrease of the latter hampered the parasitic response to NO2. Beyond 5% Cr concentration, Cr2WO6 extracts Cr from the WO3 structure, so restoring the oxygen vacancies and again increasing the parasitic NO2 response