The electrical conductivity and thermodynamic behavior of SrO-doped nonstoichiometric cerium dioxide

Abstract

Electrical conductivity and thermogravimetric measurements were made on SrO-doped nonstoichiometric cerium dioxide (i.e., Ce 1− y Sr y O 2− y− x ) as a function of temperature (∼700–1500°C) and oxygen partial pressure (∼1 to 10 −21 atm). Assuming limiting case defect models the ionic, σ i , and electronic, σ e , conductivities were calculated from this data. In the region where y ⪢ x (i.e., at low temperatures and high oxygen pressures) the conductivity is independent of P O 2 and up to approximately 3 mole% SrO, it is proportional to mole% SrO. The equation for ionic conductivity, σ i ⋍ [4.5 ± 0.5] [m/o SrO]exp(−0.58/kT) , was obtained by fitting the conductivity data in this region to an expression derived on the basis of an oxygen vacancy model. In the composition region between approximately x = 10 −3 and x = 10 −2, both the thermodynamic behavior and the electrical conductivity was shown to be consistent with a defect model involving randomly distributed doubly ionized oxygen vacancies and electrons localized on normal cerium sites. In this region the electronic conductivity varies linearly with x and the electronic mobility decreases with increasing SrO content.