Emission and Absorption Experiments on Strontium Titanate in Reducing Atmospheres

Abstract

We performed two types of experiments on polycrystalline SrTiO₃ thin films at temperatures between 573 and 1273 K in reducing gas mixtures containing CO or CH₄. Using an FT-IR spectrometer with a long-path gas cell, we analysed the composition of the gas mixture by means of absorption measurements before and after its exposure to the sample, and in a second step we measured the emission from the surface of the metal oxide. The absorption experiments revealed two different catalytically activated processes of CO oxidation, at 950 and 1100 K respectively. In the temperature region where catalytic conversion predominates, the oxidation of CO has an Eley-Rideal type characteristic, whereas the oxidation of CH₄ obeys a Langmuir-Hinshelwood mechanism. The experiments with CH₄ showed a pronounced dependence on the oxygen partial pressure above 1040 K, which could originate from reduction of the SrTiO₃ surface. We found emission from physisorbed CO₂ in CO-containing atmospheres, but no emission from adsorbed molecules was found in the experiments with CH₄.