THERMAL-ANALYSIS OF TRANSITION-METAL AND RARE-EARTH-OXIDE SYSTEM-GAS INTERACTIONS BY A SOLID ELECTROLYTE-BASED COULOMETRIC TECHNIQUE

The oxidation-reduction behaviour of transition metal and rare earth o xide systems in oxygen potential controlled atmospheres was investigat ed by means of a solid electrolyte-based coulometric technique (SEC) i n carrier gas mode to obtain information concerning the extent of oxyg en stoichiometry, the p-T-x diagram of any mixed oxide phase, the kine tics of the oxygen exchange and the phase transitions. The direct coup ling of SEC and electrical conductivity measurements provides further information about the relationship between oxygen deficiency and condu ctivity, especially as concerns the oxygen mobility and the transition from ionic to mixed ionic/electronic conductivity in any system. In t he fluorite-type phases PrO2-x, Ce0.8Pr0.2Oy-x and Ce0.8Sr0.08Pr0.12Oy -x, the higher oxidation state of Pr is stabilized and the electrical conductivity increases in this sequence. The perovskite-type phase Sr1 -yCeyFeO3-x shows transitions and a second phase reflected in the temp erature-programmed spectrum of this substance. The electrical conducti vity of Sr0.9Ce0.1FeO3-x changes from n-type to p-type with increasing oxygen pressure.