Materials in thermodynamic potential gradients

Abstract

In materials that are exposed to thermodynamic potential gradients (i.e., gradients of chemical potentials, electrical potential, temperature, or pressure), transport processes of the mobile components occur. These transport processes and the coupling between different processes are not only of fundamental interest, but are also the origin of degradation processes, such as kinetic demixing and decomposition and changes in the morphology of the material, all of which are of great practical relevance. Two classes of materials will be considered: semi-and ion-conducting oxides and ion-conducting halides. In oxides, kinetic demixing of the cations in a multicomponent oxide and kinetic decomposition of the oxide under the influence of an applied thermodynamic potential gradient will be considered for homovalent oxide solid solutions and for heterovalently doped oxides. In ion-conducting halides, the morphological stability of solid/solid interfaces, which are driven by an external electrical potential gradient, is studied. Monte Carlo simulations show that the morphological stability of the interface is determined by the difference in the ionic conductivities of the two crystals.

96Zr Tracer Diffusion in AZrO3 (A = Ca, Sr, Ba)

“…Abbreviations: ppolycrystalline; sc-single crystal; c-cubic; b-bulk; gb-grain boundaries. (1) Ho in p BaTiO3 gb [11]; (2) Ho in p BaTiO3 b [11]; (3) Ni in p Ba(Ho,Ti)O3 [10]; (4) Ni in sc BaTiO3 [10]; (5) Ni in p BaTiO3 [10]; (6) Si in MgSiO3 [39]; (7) 49 Ti in sc (La,Sr)TiO3 [25]; (8) Zr in sc BaTiO3 [12]; (9) 141 Pr in LaFeO3 gb [40; (10) 141 Pr in LaCoO3 gb [40]; (11) Co in LaCoO3 gb [41]; (12) Cr in LaMnO3 [42];(13) Mn in LaCoO3 [43]; (14) Co in LaCoO3 b [41]; (15) 141 Pr in LaMnO3 [40]; (16) Co in GdCoO3 [44]; (17) Co in EuCoO3 [44]; (18) Co in SmCoO3 [44]; (19) Co in NdCoO3 [44]; (20) Co in PrCoO3 [44]; (21) 50 Cr in (La,Ca)CrO3 gb [45]; (22) Co in LaCoO3 [44]; (23) Mn in LaMnO3 b [42]; (24) Mn in LaMnO3 gb [42]; (25) Fe in LaFeO3 gb [46]; (26) Fe in LaFeO3 b [46]; (27) 141 Pr in LaCoO3 b [40]; (28) 141 Pr in LaFeO...…”

“…Recently, it has been shown that A-site diffusion is faster than B-site diffusion in BZ [17]. Knowledge of the difference in the cation mobility at the different cation sub-lattices is vital for the understanding of the long-term stability of the materials in chemical potential gradients [19]. Moreover, cation diffusion is also relevant for the reactivity of materials with e.g., CO 2 , as recently shown for BZ-materials [20].…”

Stoichiometry Variation in Materials with Three Mobile Carriers—Thermodynamics and Transport Kinetics Exemplified for Protons, Oxygen Vacancies, and Holes

“…It can be anticipated that various ageing phenomena may be explained by such kinetics. [ 2,[46][47][48] Thus, a quantitatively precise description of the kinetics of chemical composition change, not only in simplifi ed limiting cases but in particular in the complex intermediate situations, as treated in the present publication is of outmost importance.…”

“…Even if one ionic component is overwhelmingly responsible for the ionic conductivity, this fi nite mobility of a further component leads to serious, typically unwanted long-time effects. [ 2 ] There are various situations where two ionic species can be similarly conductive, e.g., in proton conducting oxides. Though there the peculiarities appear in a most striking form and can be easily experimentally measured, the treatment to be outlined is general.…”

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

“…The present changes appear to result from a combination of the above-noted materials de-stabilization effects with gradients in oxygen chemical potential and electrical potential that are present during cell operation. It is known that morphological instabilities, kinetic decomposition, and kinetic demixing can occur in oxide materials under such gradients [18]. Gradients in the oxygen chemical potential, l O , are present at the anode/electrolyte interface since the elec- …”