MIXED CONDUCTING GAS SENSORS - ATMOSPHERE DEPENDENT ELECTRODE IMPEDANCE

A solid state oxygen sensor based on the impedance of the metal/mixed ionic-electronic conductor interface is proposed. In this study, we ex amine porous Pt electrodes in contact with (Gd1-xCax)(2)Ti2O7 with x=0 .02, 0.1. Impedance measurements monitored the electrode impedance wit hin the ranges, 650 degrees C < T < 1010 degrees C and 10(-25) atm < P O2 < 1 atm. For both materials in oxidizing environments, a simple +1/ 2 power law dependence of electrode conductance on PO2 is found at tem peratures greater than 950 degrees C, with the behavior more complex a t lower temperatures. Under reducing conditions, the x=0.1 sample show ed a -1/6 power law, while the x=0.02 sample showed a -1/4 power law. Advantages and limitations of this arrangement as an oxygen sensor are discussed.