DESCRIPTION AND CHARACTERIZATION OF A HYDROGEN-SULFIDE GAS SENSOR-BASED ON CR-2-YTIYO3+X

When heated to elevated temperatures (> 250 degrees C), the chromium t itanium oxides Cr2-yTiyO3+x displayed p-type semiconducting behaviour giving a resistance increase upon exposure to reducing gases. The mate rials show a very strong and fast response to the presence of H2S in a ir, provided they are first pre-treated with a sufficient concentratio n of this gas, for a sufficient time, at a sufficiently high temperatu re. The effect of pre-treatment was permanently to increase the baseli ne resistance in air. The pre-treatment could be reversed by heating t o temperatures greater than 420 degrees C in air, Analysis techniques such as X-ray photoelectron spectroscopy (XPS) and temperature program desorption (TPD) mass spectrometry have attributed the pre-treatment to a modification of the surface of the material by sulfur in the form of sulfate or adsorbed sulfur dioxide. The resistivity response to hy drogen sulfide was found to be square root with concentration (c(1/2)) over a wide temperature range (250-500 degrees C).