An integrated approach for determining oxygen stoichiometries in oxides

The use of a novel technique capable of measuring in-situ oxygen mass chang es in solid oxides is reported. This technique comprises an inertial, taper ed element oscillating microbalance (TEOM), the operation of which is based on the natural frequency of an oscillating tapered element containing the material and its mass. TEOM was employed to determine oxygen stoichiometrie s as a function of temperature and oxygen partial pressure for a perovskite oxide, namely La0.2Sr0.8Co0.8Fe0.2O3-delta. Experiments were performed at temperatures between 300 and 500 degreesC and oxygen partial pressures betw een 5 X 10(-4) and 1.3 X 10(-3) atm where gas atmospheres of well-defined o xygen partial pressures were generated by means of a solid state electroche mical cell. It was found that, at the conditions under consideration, oxyge n stoichiometry decreases with increasing temperature and decreasing oxygen partial pressure. Oxygen stoichiometries were also independently determine d by means of solid electrolyte coulometry (SEC) at temperatures between 30 0 and 600 degreesC and oxygen partial pressures between 1.3 X 10(-4) and 1. 3 X 10(-3) atm. The results obtained by SEC were found to be in good agreem ent with those obtained by TEOM for the range of common operating condition s. (C) 2000 Elsevier Science B.V. All rights reserved.