Oxygen diffusion and surface exchange in the mixed conducting oxides SrTi1−yFeyO3−δ. Issue 42 (17th October 2016)

• Record Type: Journal Article
• Authors: Metlenko, Veronika; Jung, WooChul; Bishop, Sean R.; Tuller, Harry L.; De Souza, Roger A.
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 42(2016)
• Page Start: 29495
• Page End: 29505
• Publication Date: 2016-10-17
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp05756j
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Variation of the surface exchange coefficient with Fe concentration suggests single mechanism of oxygen exchange for e − -poor and e − -rich SrTi1− y Fe y O3−δ oxides. Abstract : Oxygen transport in the mixed ionic–electronic conducting perovskite-oxides SrTi1− y Fe y O3− δ (with y = 0.5 and y = 1.0) was studied by oxygen isotope exchange measurements. Experiments were performed on thin-film samples that were grown by Pulsed Laser Deposition (PLD) on MgO substrates. Isotope penetration profiles were introduced by 18 O2 / 16 O2 exchanges into the plane of the films at various temperatures in the range 773 < T /K < 973 at an oxygen activity a O2 = 0.5. Isotope profiles were determined subsequently by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and their analysis yielded tracer diffusion coefficients D * and oxygen surface exchange coefficients k *. Activation energies for oxygen diffusion Δ H D * and surface exchange Δ H k * were obtained. Isothermal values of D * and values of Δ H D * are compared with literature data as a function of Fe content. D * is seen to increase monotonically with Fe content; Δ H D * shows more complex behaviour. D * and Δ H D * are also compared with the predictions of defect-chemical models. Analogous comparisons with literature data for k * and Δ H k * indicate, in contrast to prior studies, no mechanistic difference between electron-poor and electron-rich materials. It is concluded that the single operative mechanism of surface exchange for the entire series of STF compositions requires conduction-band electrons (minority electronic charge-carriers).