Electronic conductivity of Ce0.9Gd0.1O1.95−δ and Ce0.8Pr0.2O2−δ: Hebb–Wagner polarisation in the case of redox active dopants and interference

Abstract

The electronic conductivity of Ce_0.9Gd_0.1O_1.95−δ and Ce_0.8Pr_0.2O_2−δ under suppressed ionic flow was measured as a function of pO₂ in the range from 10³ atm to 10⁻¹⁷ atm for temperatures between 600 °C and 900 °C by means of Hebb–Wagner polarisation. The steady state I–V curve of Ce_0.9Gd_0.1O_1.95−δ could be well described by the standard Hebb–Wagner equation [M. H. Hebb, J. Chem. Phys., 1952, 20, 185; C. Wagner, Z. Elektrochem., 1956, 60, 4], yielding expressions for the n- and p-type conductivity as a function of pO₂. On the other hand, significant deviation of the steady state I–V curve from the standard Hebb–Wagner equation was observed for the case of Ce_0.8Pr_0.2O_2−δ. It is shown that the I–V curve can be successfully reproduced when the presence of the redox active dopant, Pr³⁺/Pr⁴⁺, is taken into account, whereas even better agreement can be reached when further taking into account the interference between the ionic and electronic flows [C. Chatzichristodoulou, W.-S. Park, H.-S. Kim, P. V. Hendriksen and H.-I. Yoo, Phys. Chem. Chem. Phys., 2010, 12, 33]. Expressions are deduced for the small polaron mobilities in the Ce 4f and Pr 4f bands of Ce_0.8Pr_0.2O_2−δ.