Investigation of n-type electronic defects in the protonic conductor SrCe1-xYxO3-delta

Rare earth doped strontium cerates show mixed conduction by protons, oxygen ions and electronic defects in wet hydrogen or oxygen atmospheres at high temperatures. In order to characterize the n-type electronic defects, conductivity measurements using the Hebb-Wagner polarization technique at high temperatures were performed in wet hydrogen atmospheres. In addition, absolute concentrations, [Ce3+], of the magnetic Ce3+-ion were determined from magnetization measurements at 1.8 K on quenched samples. Between 400 degrees C less than or equal to T less than or equal to 800 degrees C and between 10 Pa less than or equal to p(H2)less than or equal to 10(5) Pa and 10(2) Pa less than or equal to p(H2O)less than or equal to 2 . 10(4) Pa, the electronic conductivity, sigma(n), is observed to vary like p(H2)(1/4) and to be independent of p(H2O). The comparison of these results with defect models for the hydrogen/water incorporation and for the oxygen-loss in reducing atmospheres indicates that in the explored range of temperatures and partial pressures the e' responsible for sigma(n) are largely compensated by OHo. (wet situation with V(o)(..)less than or equal to OHo.). In addition, the Y-Cel-ions in the doped samples must, to a large extent, be present as rather stable electrically neutral complexes, e.g., as (Y'V-Ce(O).) or (Y'(CeVOY)-Y-..'(Ce)). The temperature dependence of sigma(n) shows an Arrhenius-behaviour with Delta H-n = 1.2 eV and Delta H-n = 1.5 eV for the undoped and doped sample, respectively indicating different e' mobilities in both sample types. The variation of [Ce3+] determined magnetically with p(H2) and p(H2O) indicates a partial decomposition of the samples (formation of Ce2O3 during their exposure to H-2/H2O-atmospheres at high temperatures.