Crystalline Oxide Solid Solutions in Oxygen Potential Gradients

Abstract

The steady state demixing of an initially homogeneous oxide solid solution (A, B)0 in an oxygen potential field is studied theoretically and experimentally.In case that D\ > DB Do > the crystal is shifted with respect to the oxide lattice system toward the higher oxygen potential and is enriched in A at the side of the higher oxygen potential, while the transport of oxygen in the crystal is negligible. A numerical solution of the transport problem is presented, and the predicted effect is verified experimentally.

Operational Inhomogeneities in La0.9Sr0.1Ga0.8Mg0.2O3–δ Electrolytes and La0.8Sr0.2Cr0.82Ru0.18O3–δ–Ce0.9Gd0.1O2–δ Composite Anodes for Solid Oxide Fuel Cells

“…Although, cation diffusivities are normally several orders of magnitude lower than that of oxygen ions [21], at sufficiently long times, high temperatures [22], and electric fields [23][24][25], substantial cation migration may still occur. Note that the migration of the different cations are not identical; certain elements migrate faster, others slower [26]. We can expect the appropriate gradient terms and concentration changes to be appreciable over a region of about 1 lm from the interface [27], consistent with the experimental results.…”

Materials in thermodynamic potential gradients

“…The phenomenon of kinetic demixing was first analyzed by Schmalzried et al [7] and experimentally demonstrated using as a model system the oxide solid solution (Co 1-x Mg x )O, where Co is the faster component. As expected, strong enrichment of Co was found at the high-p O 2 side of the material.…”

“…8), whereas in the latter case, the cross-coefficients have to be considered. [7], the demixing profile is then obtained by integration of eq. 11 with appropriate boundary conditions.…”

On the Soret effect in binary nonstoichiometric oxides—kinetic demixing of cuprite in a temperature gradient

“…Under working conditions, these materials are often exposed to external forces causing both reactions and transport within the materials. Prominent examples are electromigration or kinetic demixing in electric fields [1][2][3][4][5], kinetic demixing in chemical potential gradients [6][7][8][9], stress-driven segregation [10,11] or thermodiffusion ( [12][13][14][15][16][17][18][19][20], see [21,22] for reviews).…”