Oxygen Nonstoichiometry and Defect Chemistry Modeling of Ce[sub 0.8]Pr[sub 0.2]O[sub 2−δ]

Abstract

The oxygen nonstoichiometry (δ) of Ce0.8Pr0.2normalO2−δ has been measured as a function of PnormalO2 at temperatures between 600 and 900°C by coulometric titration and thermogravimetry. An ideal solution defect model, a regular solution model, and a defect association model, taking into account the association of reduced dopant species and oxygen vacancies, were unable to reproduce the experimental results. However, excellent agreement with the experimentally determined oxygen nonstoichiometry could be achieved when using either a nonideal solution model with an excess enthalpic term linear in δ (ΔHPrexc=anormalHδ) and a completely random distribution of defects (referred to as “δ-linear”), or a “generalized δ-linear” solution model, where the excess Gibbs energy change in the reduction reaction of the dopant linearly varies with δ (ΔGPrexc=anormalGδ) . A comparison of the partial molar enthalpy and entropy of oxidation, estimated from the defect models with those determined directly from the oxygen nonstoichiometry, suggests that the δ-linear solution model is the most appropriate in accounting for the observed nonideal reduction behavior of Pr.

Chemomechanical properties and microstructural stability of nanocrystalline Pr-doped ceria: An in situ X-ray diffraction investigation

“…The chemical expansion arises upon the reduction of Pr 4+ and/or Ce 4+ cations to their respective +3 valance states [16,17]. It is known that Pr 4± reduces to Pr 3± at lower temperatures compared to Ce 4± reduction to Ce 3± due to the lower enthalpy of reduction of Pr 3± .…”

Ionic/Electronic Conductivity, Thermal/Chemical Expansion and Oxygen Permeation in Pr and Gd Co-Doped Ceria PrxGd0.1Ce0.9-xO1.95-δ

“…In several studies, 17,20,25 it has been reported that the electronic conductivity of Pr-doped ceria can be well described by a small polaron mechanism. Hence, mobility and conductivity will scale with temperature according to:…”

Electronic and Ionic Transport in Ce0.8PrxTb0.2−xO2−δand Evaluation of Performance as Oxygen Permeation Membranes

“…37 Disk shaped samples and rods were prepared at a uniaxial pressure of ∼3 MPa and further isostatic pressure of 325 MPa. The specimens were sintered at 1500…”

“…Based on the a O2 dependency of the oxygen nonstoichiometry of Ce 0.8 Pr x Tb 0.2−x O 2−δ , 37 it is expected that during the largest part of the I-V curve the condition ∇μ i ≈ 0 is valid for part of the material, the rest complying to the condition ∇μ i = 0. When the established oxygen activity range in a Hebb-Wagner polarization experiment covers several defect regimes, a single Hebb-Wagner type equation, 42,43 of the form:…”