Yttria-doped Ceria Research Articles

Effects of long-range forces on oxygen transport in yttria-doped ceria: simulation and theory

Oxygen transport in many ionically conducting oxides occurs by diffusion or migration of oxygen-ion vacancies. An important issue in our understanding of these materials is the mechanism by which vacancies become trapped or ordered, and how this process affects transport. In this paper we reinvestigate the mechanism of vacancy trapping in yttria-doped ceria, and show that long-range forces play an important role in the transport properties of this material. We demonstrate, using dynamic Monte Carlo (MC) simulation, that these long-range forces cause strong deviations from the behaviour predicted by a simple point-defect model, deviations which are evident in previously published measurements of the conductivity. Interpretation of the physics observed in the simulation leads naturally to a Debye–Huckel modification of the point-defect model, which, when combined with kinetic parameters extracted independently from NMR spectroscopy, is capable of predicting measured macroscopic transport with no adjustable parameters. We find that in the case of yttria-doped ceria, the vacancy–defect association enthalpy is well approximated by considering only Coulombic interactions.

Dielectric relaxation in YTTRIA-doped Ceria solid solutions

The nature of the defects present in Y 2O 3-doped CeO 2 is explored by means of dielectric relaxation, employing primarily the thermally-stimulated depolarization current (TSDC) technique. For Y 2O 3 concentrations ⩽ 1 mole %, two relaxation peaks are observed. The lower-temperature peak shows a dielectric relaxation rate, τ −1 which is 1 2 the relaxation rate of the corresponding anelastic relaxation. This proves that the peak is due to nn, 〈111〉 oriented, (Y V O) pairs, where V O represents the oxygen vacancy. These pairs are positively charged defects which are compensated by an equal number of isolated Ý. The upper peak is a broad peak whose position varies with Y 2O 3 concentration in the same manner as the activation enthalpy for the ionic conductivity. The peak is not due to simple dipoles, but to relaxation of the array of alternately charged (Y V O) and Ý defects by the redistribution of oxygen-ion vacancies. A simple model, in which these defects form a superlattice containing wrong pairs, explains the essential features of the upper peak.

ChemInform Abstract: PREPARATION OF HIGH‐DENSITY CERIA‐YTTRIA CERAMICS

AbstractDie aus Ce‐Y‐Oxidpulvern durch Heißpressen erzeugte Keramik hat Fluoritstruktur mit einer Gitterkonstanten von 0.541088 nm und die Zusammensetzung Ce0‐914Y0‐"35O,‐957.

Oxygen-ion conductivity and defect interactions in yttria-doped ceria

Conductivity, σ, of the oxygen-ion conductivity solid electrolyte system CeO 2:Y 2O 3 is studied in detail as a function of temperature and dopant concentration, c 0, from 0.05 to 40 mole% Y 2O 3. It is shown that the well-known maximum in σ versus c 0 is composed of two distinct ranges. In the dilute range (<1%Y 2O 3), an oxygen vacancy is associated with one Y 3+ ion to form a charged (incompletely compensated) pair. Here σ increases, due to a linear decrease in association enthalpy H A with c 1 3 0 resulting from electrostatic interactions. In the high-concentration range, on the other hand, σ decreases and H A increases due to the development of deep vacancy traps.