Water incorporation in oxides: A moving boundary problem

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

“…This behavior, which arises here simply from the coupling of the three defects according to Equations ( 18) - ( 32) to be heuristically implemented into preceding phenomenological simulations to properly describe the concentration profi les arising in slightly Fe-doped SrTiO 3 single crystals after a p H O 2 change. [ 12 ] The fact that the minimum in [h • ] marks the boundary between the regions with different effective H diffusivities can be understood, e.g., from Equation ( 30) • ] (more examples can be found in Poetzsch et al) [ 19 ] The lower effective hydrogen diffusivity in the growing outer (reoxidized) zone acts as a throttle valve for hydrogen supply to the inner zone with high diffusivity, and limits the maximum transient reduction developed in the sample.…”

“…This was already recognized in the literature. [ 12 ] leading to the introduction of a "moving boundary." Because the fl ux of one defect as given by Equations ( 18) - ( 32) , ∇ ∇ and all gradients evolving in time and space), it is obvious that the fl uxes of the different defects are related to each other in a complex way.…”

“…Fe-doped SrTiO 3 in the literature). [ 12 ] Part II [ 19 ] will explore the relations between the degree of decoupling and several material parameters, and investigate also relaxations after O2 p changes. To be precise in terminology we will use the term twocomponent diffusion to describe the general case (diffusion of H and O, which degenerates to single component diffusion, e.g., H 2 O, under special conditions).…”

Ab initio charge analysis of pure and hydrogenated perovskites

“…6,7 Here, the proton is assumed to bind to a lattice oxygen, O O x , and form a hydroxyl defect, OH O • , implying full dissociation of proton and electron. The electron, eЈ, is believed to transfer to the conduction band or associate with another defect.…”

Moving boundary diffusion problem for hydration kinetics evidenced in non-monotonic conductivity relaxations of proton conducting perovskites

“…Since the first reports on water incorporation kinetics in an FeSrTiO 3 − δ single crystal by Yu et al [5,6], and in Yb-doped ScCeO 3 − δ polycrystal [7], non-monotonic conductivity relaxations have been confirmed as general phenomena for the proton ceramic conductors in perovskite or related structure in p-type oxidized regime [8][9][10][11][12][13][14][15]. The relaxation has been modeled as the superposition of the decoupled hydrogen and oxygen diffusion, although the spatially-resolved optical spectroscopy on Fe-SrTiO 3 − δ single crystals revealed, a rather involved but realistic moving boundary diffusion phenomena [5,6], viz., the faster hydrogen in-diffusion proceeding from the hydration front developing into the sample, not from the sample surface.…”