Elaboration and characterization of tin oxide–lanthanum oxide mixed layers prepared by the electrostatic spray pyrolysis technique

Lanthanum oxide–tin oxide mixed layer was found to show promising sensing properties to CO2 in the air. In this paper, we describe the characterization of such layers fabricated by the electrostatic spray pyrolysis technique. Analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM) show a structure of grain aggregates, while energy dispersion analysis reveal that the original and final compositions are very close with an uniformly distribution in the layer. X-ray diffraction gives the nature of the deposited oxide, which is LaOCl and SnO2. Electrical characterization versus temperature and concentration reveal a sensitivity peak for the 2% lanthanum oxide mixed layer at about 425°C. A variable frequency (13 MHz–500 Hz) ac voltage was applied to all the sensor structures to perform the complex impedance spectrum measurements, at a temperature range 350–550°C, and a CO2 concentration range 400–2000 ppm in synthetic air. For all these measurements, we obtain the same equivalent circuit, which fits very well the experimental data, and allows us to propose a conduction model.