Modification of sensitivity of BaSnO 3 sensor due to parameters of synthesis and formation of the device
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ederico Schipani and Celso M. Aldao Catalysts and Surfaces Division, INTEMA, National University of Mar del Plata, Mar del Plata 7600, Argentina
Jorge E. Rodríguez-Páez Department of Physics, CYTEMAC Group, University of Cauca, Popayán 90002, Colombia
Miguel A. Ponce Catalysts and Surfaces Division, INTEMA, National University of Mar del Plata, Mar del Plata 7600, Argentina (Received 1 June 2015; accepted 23 September 2015)
Powders of BaSnO3 were synthesized to obtain gas sensor thick films (using the screen printing technique) for the detection of O2 and CO. Impedance spectroscopy was used at different atmospheres and temperatures. In the presence of O2, the films showed a maximum value of sensitivity at 300 °C, with the powders formed by Pechini presenting greater reproducibility and sensitivity (with an order of magnitude greater than that for the powders formed by precipitation). Results showed that the films formed with powders obtained using the Pechini method presented a better response to CO, with a maximum sensitivity at 450 °C. In addition, in the presence of CO and for T . 250 °C, these films showed an anomalous behavior regarding their sensitivity as a function of time when platinum electrodes were used: a great increase in the electrical resistance value for exposure times greater than 10 min.
I. INTRODUCTION
The BaO–SnO2 binary system is known to have three compounds: BaSnO3, Ba3Sn2O7, and Ba2SnO4. The first of the three is the best known, most researched, and most useful. Barium stannate, BaSnO3, has a cubic perovskite structure.1 It is the most widely used oxide for technological applications due to its dielectric properties, standing out as a capacitor, varistor, transparent electrocatalytic conductive electrode, and photovoltaic cell, in photocatalytic applications, and as a gas sensor.2–4 Ceramic powders of BaSnO3 are usually obtained by a solid state reaction between BaCO3 and SnO2 at 1000–1400 °C.5,6 Other techniques that have been used include hydrothermal,7,8 considering the effect of different solvents,9 sol–gel,10 self-heat-sustained route,11 modified combustion,12 and reverse micelle method.13 The interest in this perovskite is mainly due to the easy modification of its electrical properties and its stability at high temperatures. For gas sensing, BaSnO3 is a very promising material for high-temperature detection of gases,2 particularly those gases generated in combustion processes. It has been reported that BaSnO3 has a 3.4 eV band gap, which is within the range generally desired for gas sensor materials.14,15 Contributing Editor: José Arana Varela a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.318 J. Mater. Res., Vol. 30, No. 22, Nov 27, 2015
In polycrystalline materials, it is widely accepted that barriers formed between particles or grains have a Schottky-type nature and this governs their electrical behavior. Adsorption of gaseous species at the grain boundaries can induce changes in barrier heights and in donor concentrations. Many oxi
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