Skiba Emily J, Chen Ting, Perry Nicola H
Department of Materials Science & Engineering and Materials Research Laboratory, University of Illinois at Urbana-Champaign, 1304 W Green St, Urbana, Illinois 61801, United States.
International Institute for Carbon-Neutral Energy Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395 Japan.
ACS Appl Mater Interfaces. 2020 Oct 28;12(43):48614-48630. doi: 10.1021/acsami.0c14265. Epub 2020 Oct 19.
The oxygen surface exchange coefficient () dictates the efficiency and response time of many mixed conductors, so its accurate, continuous measurement in realistic conditions, enabling rational tailoring, is necessary. However, recent results showed that values determined by a thin-film optical transmission relaxation (OTR) method were orders of magnitude lower than those extracted from the cross-cell AC-impedance spectroscopy (AC-IS) approach, and similar discrepancies among methods exist in the literature. OTR has also detected dramatic increases in in situ during crystallization. Therefore, in this work, we sought to establish whether values from OTR are reliable, and to gain further insight into crystallization-induced changes, via comparison to the electrical conductivity relaxation (ECR) method. We performed simultaneous OTR and ECR measurements on the same region of an as-grown amorphous SrTiFeO (STF) film, prepared by pulsed laser deposition and characterized by Rutherford backscattering spectrometry, during thermal treatment to induce crystallization and a large increase in . We also compared cross-cell AC-IS vs OTR on an as-grown amorphous film during crystallization and OTR vs ECR on a crystalline-grown film. Simultaneous measurements eliminate variability in between samples or due to different thermal/gas history. OTR and ECR methods yielded the same values, and the same crystallization temperature, within error. Both isothermal optical absorption and electrical conductivity changes are proportional to the hole and oxygen concentration changes under the conditions of this study. However, while OTR was able to measure optical absorption changes under all of the conditions tested, ECR was not viable in the high-resistance regime. Cross-cell AC-IS values were elevated vs OTR values, were less stable over time, and were only accessible in limited conditions. We discuss the potential impacts of current collectors and oxygen exchange driving force on values determined by cross-cell AC-IS vs ECR vs OTR.
氧表面交换系数（ ）决定了许多混合导体的效率和响应时间，因此在实际条件下对其进行准确、连续的测量，以实现合理的定制是必要的。然而，最近的结果表明，通过薄膜光学传输弛豫（OTR）方法测定的 值比从交叉电池交流阻抗谱（AC-IS）方法提取的值低几个数量级，并且文献中各方法之间也存在类似的差异。OTR还检测到结晶过程中原位 的急剧增加。因此，在这项工作中，我们试图确定OTR得到的 值是否可靠，并通过与电导率弛豫（ECR）方法比较，进一步深入了解结晶诱导的变化。我们对通过脉冲激光沉积制备并通过卢瑟福背散射光谱表征的生长态非晶SrTiFeO（STF）薄膜的同一区域进行了同步OTR和ECR测量，在热处理过程中诱导结晶并使 大幅增加。我们还比较了生长态非晶薄膜结晶过程中交叉电池AC-IS与OTR以及晶态生长薄膜上OTR与ECR的情况。同步测量消除了样品之间或由于不同热/气体历史导致的 的变化。OTR和ECR方法在误差范围内得到了相同的 值和相同的结晶温度。在本研究条件下，等温光吸收和电导率变化均与空穴和氧浓度变化成正比。然而，虽然OTR能够在所有测试条件下测量光吸收变化，但ECR在高电阻状态下不可行。交叉电池AC-IS的 值相对于OTR值升高，随时间稳定性较差，并且仅在有限条件下可获得。我们讨论了集电器和氧交换驱动力对交叉电池AC-IS与ECR与OTR测定的 值的潜在影响。
