ENEA C.R. Casaccia - Sala Blu 10.30 a.m., April 16th, 1999

 

SEMICONDUCTING OXIDE THICK-FILM SENSORS FOR ENVIRONMENTAL MONITORING:

FROM THE POWDER TO THE DEVICE

 

Enrico Traversa

Department of Chemical Science and Technology - II University of Rome

Via della Ricerca Scientifica, 00133, Rome, Italy

 

Environmental monitoring is one of the most desired amongst the numerous industrial and civil applications for which the development of reliable solid-state gas sensors is demanded. For this application, sensors able to selectively detect the various gases at a concentration level of a few ppb are needed. The methods for air quality control currently approved by the standards consist in analytical techniques, which need the use of very costly and bulky equipments. In this paper, we report results about the use of thick film gas sensors based on semiconducting oxides in laboratory and environmental monitoring field tests. TiO2-based, LaFeO3 and SmFeO3 thick films were produced by screen-printing technology on alumina substrates with comb-type Au electrodes. Nanosized perovskite-type oxide powders used for the preparation of the thick films were prepared by the thermal decomposition at 700°C of hexacyanocomplexes. Nanosized pure and Ta-doped TiO2 powders were prepared using a sol-gel technique. The films have been fired at different temperatures, in N2 and air atmospheres. We used perovskite-type oxides because they are p-type semiconducting oxides, while TiO2 is an n-type semiconductors, like the oxides commonly used for gas sensors. The use of p-type semiconducting oxides gives a potential advantage for the detection of oxidizing gases, such as NO2, and for the preparation of sensor arrays. The gas-sensitive electrical response of the thick films were tested in laboratory, in environments with different gases (CO and NO2) in dry and wet air. The field tests were performed by measuring the variation of conductivity of Ta-doped TiO2, LaFeO3 and SmFeO3 thick films exposed to real atmosphere. The prototype sensors were placed in a sensor array with other semiconducting oxides thick-film sensors, like SnO2 and In2O3, beside a traffic light in Ferrara at the same place where a conventional station of environmental monitoring is located. The sensors' electrical response was compared with the results of the analytical instruments for environmental monitoring. The same trend was observed for both systems, with very promising results. This allows us to consider as feasible the use of oxide sensors for cheap, innovative stations for environmental monitoring.

The lecture is based on the results reported or related to the following papers:

1. E. Traversa, P. Nunziante, G. Gusmano, M. Sakamoto, and Y. Sadaoka, "Low-Temperature Preparation of Nanosized, Crystalline LaFeO3 Powders", Mater. Sci. Forum, 203 (1996) 47-51.

2. E. Traversa, M. Sakamoto, and Y. Sadaoka, "Mechanism of LaFeO3 Perovskite-Type Oxide Formation from the Thermal Decomposition of d-f Heteronuclear Complex La[Fe(CN)6].5H2O", J. Am. Ceram. Soc., 79 (1996) 1401-1404.

3. M.C. Carotta, M.A. Butturi, G. Martinelli, Y. Sadaoka, P. Nunziante, and E. Traversa, "Microstructural Evolution of Nanosized LaFeO3 Powders Prepared from the Thermal Decomposition of a Cyano-Complex for Thick Film Gas Sensors", Sens. Actuators B, 44 (1997) 590-594.

4. E. Traversa, P. Nunziante, M. Sakamoto, Y. Sadaoka, M.C. Carotta, and G. Martinelli, "Thermal Evolution of the Microstructure of Nanosized LaFeO3 Powders from the Thermal Decomposition of a Heteronuclear Complex, La[Fe(CN)6].5H2O", J. Mater. Res., 13 (1998) 1335-1344.

5. M.C. Carotta, G. Martinelli, Y. Sadaoka, P. Nunziante, and E. Traversa, "Gas-Sensitive Electrical Properties of Perovskite-Type SmFeO3 Thick Films", Sens. Actuators B, 48 (1998) 270-276.

6. Y. Sadaoka, H. Aono, E. Traversa, and M. Sakamoto, "Thermal Evolution of Nanosized LaFeO3 Powders from a Heteronuclear Complex, La[Fe(CN)6].nH2O", J. of Alloys and Compounds, 278 (1998) 135-141.

7. E. Traversa, M. Sakamoto, and Y. Sadaoka, "A Chemical Route for the Preparation of Nanosized Rare Earth Perovskite-Type Oxides for Electroceramic Applications", Particulate Science and Technology, xx (1998) in press. (Invited).

8. G. Martinelli, M.C. Carotta, M. Ferroni, Y. Sadaoka, and E. Traversa, "Screen-Printed Perovskite-Type Oxide Thick Films as Gas Sensors for Environmental Monitoring", accepted for publication in Sens. Actuators B, xx (1999) in press. (Invited).

9. M.C. Carotta, M.A. Butturi, G. Martinelli, M.L. Di Vona, S. Licoccia, and E. Traversa, "Thick Film Microsensors Based on Nanosized Titania Sol-Gel Powder", accepted for publ. in Electron Technology.

10. G. Martinelli, M.C. Carotta, E. Traversa, and G. Ghiotti, "Thick Film Microsensors Based on Nanosized Semiconducting Oxide Powders", accepted for publication in Materials Research Society Bulletin, special issue "Gas Sensing Materials", ed. by K. Ihokura and J. Watson. (Invited).

11. E. Traversa, Y. Sadaoka, M.C. Carotta, and G. Martinelli, "Environmental Monitoring Field Tests Using Screen-Printed Thick-Film Sensors Based on Semiconducting Oxides", submitted for publication in Sens. Actuators B. 
 
 

Enrico Traversa received a Laurea (Italian doctoral degree) in Chemical Engineering from the University of Rome "La Sapienza". In 1988, he joined the Dipartimento di Scienze e Tecnologie Chimiche, Faculty of Engineering of the University of Rome "Tor Vergata", where since 1992 he is Associate Professor of Materials Technology. His studies, documented by 4 patents, 1 book, and more than 140 papers mainly published on International Journals and on the Proceedings of International Conferences, started in the field of metal corrosion and protection and lately changed to electroceramics. His research interests include at present the preparation of nanosized electroceramic powders with non-conventional methods and their characterization, the development of gas sensors for environmental monitoring, the design of multiphase materials for chemical sensors with novel detection methods, and the preparation of nanocomposites with functional properties. He was the recipient of several grants used to visit Japan, amongst them, a grant within the framework of the European Union S&T Grant in Japan, for 6 months spent at the RCAST of the University of Tokyo. He is member of the International Board of the Journal of Electroceramics. For the same journal, he co-edited a special issue on "Ceramic Sensors". He participated to several International Conferences as invited Speaker. He gave seminars at many prestigious institutions in Japan and worldwide (Norway, Korea, Taiwan, India, Thailand, Slovenia, USA and UK). Traversa can be reached at the Dipartimento di Scienze e Tecnologie Chimiche, Universita' di Roma "Tor Vergata", Via della Ricerca Scientifica, 00133 Rome, Italy; phone +39-06-7259-4492; fax +39-06-7259-4328; e-mail traversa@uniroma2.it.

Other main publications relevant to the sensor field:

* G. Gusmano, G. Montesperelli, E. Traversa, and G. Mattogno, "Microstructure and Electrical Properties of MgAl2O4 Thin-Films for Humidity Sensing", J. Am. Ceram. Soc., 76 (1993) 743-750.

* G. Gusmano, G. Montesperelli, P. Nunziante, and E. Traversa, "Microstructure and Electrical Properties of MgAl2O4 and MgFe2O4 Spinel Porous Compacts for Use in Humidity Sensors", Br. Ceram. Trans., 92 (1993) 104-108.

* G. Gusmano, G. Montesperelli, P. Nunziante, and E. Traversa, "Study of the Conduction Mechanism of MgAl2O4 at Different Environmental Humidities", Electrochimica Acta, 38 (1993) 2617-2621.

* E. Traversa, M. Miyayama, and H. Yanagida, "Gas Sensitivity of ZnO/La2CuO4 Heterocontacts", Sens. Actuators B, 17 (1994) 257-261.

* A. Bearzotti, A. Bianco, G. Montesperelli, and E. Traversa, "Humidity Sensitivity of Sputtered TiO2 Thin Films", Sens. Actuators B, 19 (1994) 525-528.

* G. Mattogno, G. Righini, G. Montesperelli, and E. Traversa, "X-Ray Photoelectron Spectroscopy Investigation of MgAl2O4 Thin-Films for Humidity Sensors", J. Mater. Res., 9 (1994) 1426-1433.

* E. Traversa and A. Bearzotti, "Humidity Sensitive Electrical Properties of Dense ZnO with Non-Ohmic Electrode", J. Ceram. Soc. Jpn., 103 (1995) 11-15.

* E. Traversa, "Ceramic Sensors for Humidity Detection: The State-of-the-Art and Future Developments", Sens. Actuators B, 23 (1995) 135-156.

* E. Traversa, S. Matsushima, G. Okada, Y. Sadaoka, Y. Sakai, and K. Watanabe, "NO2 Sensitive LaFeO3 Thin Films Prepared by r.f. Sputtering", Sens. Actuators B, 25 (1995) 661-664.

* G. Montesperelli, A. Pumo, E. Traversa, G. Gusmano, A. Bearzotti, A. Montenero, and G. Gnappi, "Sol-Gel Processed TiO2-Based Thin Films as Innovative Humidity Sensors", Sens. Actuators B,, 25 (1995) 705-709.

* E. Traversa, A. Bearzotti, M. Miyayama, and H. Yanagida, "The Electrical Properties of La2CuO4/ZnO Heterocontacts at Different Relative Humidities", J. Mater. Res., 10 (1995) 2286-2294.

* E. Traversa, "Design of Ceramic Materials for Chemical Sensors with Novel Properties", J. Am. Ceram. Soc., 78 (1995) 2625-2632.

* E. Traversa, A. Montenero, and G. Gusmano, "Innovative Humidity Sensitive Electrical Properties of Sol-Gel Processed Ceramic Thin Films", Eur. J. Solid State Inorg. Chem., special issue "Advanced Materials and Processing", ed. by M. Yoshimura, 32 (1995) 719-729. (Invited).

* E. Traversa, "Intelligent Ceramic Materials for Chemical Sensors", J. Intelligent Mater. Systems and Structures. 6 (1995) 860-869.

* E. Traversa, G. Gnappi, A. Montenero, and G. Gusmano, "Ceramic Thin Films by Sol-Gel Processing as Novel Materials for Integrated Humidity Sensors", Sens. Actuators B, 31 (1996) 59-70. (Invited).

* G. Gusmano, A. Bianco, G. Montesperelli, and E. Traversa, "An EIS Study of the Humidity Sensitive Electrical Conduction of Alkali-Doped TiO2 Films", Electrochim. Acta, 41 (1996) 1359-1368.

* E. Traversa, A. Bearzotti, M. Miyayama, and H. Yanagida, "Influence of the Electrode Materials on the Electrical Response of ZnO-Based Contact Sensors", J. Eur. Ceram. Soc., 18 (1998) 621-631.

* G. Gusmano and E. Traversa, "Rare Earth Perovskite-Type Oxide as Gas Sensors", Kovine Zlitine Tehnologije (Metal Alloys Technologies), 32 (1998) 501-506. (Invited).

* E. Traversa, L. Montanaro, H. Aono, and Y. Sadaoka, "Sol-Gel Synthesis, Sintering and Electrical Properties of NASICON Having New Compositions, Na3Zr2-(x/4)Si2-xP1+xO12", in Ceramic Transactions, Vol. 95: Sol-Gel Synthesis and Processing, ed. by S. Komarneni, S. Sakka, P.P. Phule' and R.M. Laine, The Am. Ceram. Soc., Westerville, Ohio, USA, 1999, pp. 225-234.

* M.L. Di Vona, S. Licoccia, L. Montanaro, and E. Traversa, "Sol-Gel Synthesis of NASICON: 1 and 2D NMR Investigation", Chem. Mater., xx (1999) in press. 

* E. Traversa, S. Villanti, G. Gusmano, and Y. Sadaoka, "Design of Ceramic Materials for Chemical Sensors: SmFeO3 Thick Films Sensitive to NO2", accepted for publication in J. Am. Ceram. Soc.. 

* H. Aono, Y. Sadaoka, E. Traversa, and L. Montanaro, "Electrical Properties of Sol-Gel Processed NASICON Having New Compositions", submitted for publication in Sens. Actuators B. 

* E. Traversa, L. Montanaro, H. Aono, and Y. Sadaoka, "Synthesis of NASICON with New Compositions for Electrochemical Carbon Dioxide Sensors", submitted for publication in J. Electroceramics.

* Y. Shimizu, E. Di Bartolomeo, E. Traversa, G. Gusmano, T. Hyodo, K. Wada, and M. Egashira, "Effect of Surface Modification on NO2 Sensing Properties of SnO2 Varistor-Type Sensors", submitted for publication in Sensors and Actuators B.

 

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