Metlenko Veronika, Jung WooChul, Bishop Sean R, Tuller Harry L, De Souza Roger A
Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany.
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Phys Chem Chem Phys. 2016 Oct 26;18(42):29495-29505. doi: 10.1039/c6cp05756j.
Oxygen transport in the mixed ionic-electronic conducting perovskite-oxides SrTiFeO (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 O/O exchanges into the plane of the films at various temperatures in the range 773 < T/K < 973 at an oxygen activity aO = 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 ΔH and surface exchange ΔH were obtained. Isothermal values of D* and values of ΔH are compared with literature data as a function of Fe content. D* is seen to increase monotonically with Fe content; ΔH shows more complex behaviour. D* and ΔH are also compared with the predictions of defect-chemical models. Analogous comparisons with literature data for k* and ΔH 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).
通过氧同位素交换测量研究了混合离子 - 电子导电钙钛矿氧化物SrTiFeO（y = 0.5和y = 1.0）中的氧传输。实验在通过脉冲激光沉积（PLD）在MgO衬底上生长的薄膜样品上进行。在氧活度aO = 0.5时，在773 < T/K < 973的不同温度下，通过O/O交换在薄膜平面内引入同位素渗透剖面。随后通过飞行时间二次离子质谱（ToF - SIMS）确定同位素剖面，对其分析得出示踪剂扩散系数D和氧表面交换系数k。获得了氧扩散的活化能ΔH和表面交换的活化能ΔH。将D的等温值和ΔH的值作为Fe含量的函数与文献数据进行比较。可以看出D随Fe含量单调增加；ΔH表现出更复杂的行为。还将D和ΔH与缺陷化学模型的预测进行了比较。与文献中k和ΔH数据的类似比较表明，与先前的研究相比，贫电子和富电子材料之间没有机理差异。得出结论，整个STF组成系列的单一表面交换操作机制需要导带电子（少数电子电荷载流子）。
