Electrical behavior of SnO2 polycrystalline ceramic pieces formed by slip Casting: effect of surrounding atmosphere (Air and CO)

Abstract

Pieces of porous polycrystalline SnO2 with and without cobalt have beenformed by the slip-casting method, using ceramic powders synthesized by thecontrolled precipitation method. A suitable methodology was developed forforming and sintering the pieces to enable controlled modification of theirmicrostructure, principally grain size, porosity, and type of intergranularcontacts. Better control of the microstructure was obtained in the samplescontaining cobalt. In these, predominance of open necks and intergranularcontacts was observed, which can represent Schottky barriers. Because of itsgood structural homogeneity, porosity, and small grain size (of the order of1 lm), the sample with 2 mol.% Co sintered at 1250C for 2 h was selected forelectrical characterization by complex impedance spectroscopy, varying theoperating temperature, concentration and nature of the surrounding gas (airor CO), and bias voltage. The resulting Rp and Cp curves were very sensitive tovariation in these parameters, being most obvious for the Cp curves, whichshowed a phenomenon of low-frequency dispersion when bias voltages otherthan zero were used, in the presence of O2, and at operating temperature of280C. The electrical behavior of the SnO2 with 2 mol.% Co sample sintered at1250C was consistent with the nature and microstructural characteristics ofthe active material and was justified based on the presence of shallow- anddeep-type defects, and variations in barrier height and width, caused byadsorption of gas molecules.