Origins and Control of Optical Absorption in a Nondilute Oxide Solid Solution: Sr(Ti,Fe)O3–x Perovskite Case Study,Chemistry of Materials

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Origins and Control of Optical Absorption in a Nondilute Oxide Solid Solution: Sr(Ti,Fe)O3–x Perovskite Case Study
Chemistry of Materials ( IF 7.2 ) Pub Date : 2019-01-10 00:00:00 , DOI: 10.1021/acs.chemmater.8b04580
Nicola H. Perry _{1,

2} , Namhoon Kim ₃ , Elif Ertekin _{2,

3} , Harry L. Tuller _{2,

4}

Affiliation

Understanding and rationally tailoring defect-mediated optical absorption of nondilute oxide solid solutions represents a complex challenge. In this work, we investigate compositions in the SrTiO₃–SrFeO_2.5 solid solution, departing from the simpler dilute Fe-substituted SrTiO₃ case. Through ex situ and in situ optical absorption measurements of mixed conducting thin films prepared by pulsed laser deposition and through density functional theory simulations, we demonstrate understanding and rational tailoring of the optical absorption behavior. Experimentally, broad subgap absorption peaks, centered around 2.1 and 2.8–3 eV, increase in intensity with increasing Fe and/or O concentrations and decrease with increasing La donor dopant concentration. Consistent with these observations, the absorption is found to be proportional to the hole concentration and to the Fe concentration under fully oxidized conditions. This behavior is similar to the dilute case; however, the solid solution electronic structure and optical absorption behavior cannot be represented simply by Fermi level shifts in a rigid-band model. Simulations confirm these trends and identify transitions responsible for absorption as occurring from within the valence band to empty states at the hybrid (O 2p/Fe 3d) valence band maximum and to empty states at the hybrid (Ti/Fe 3d) conduction band minimum. Adding oxygen or iron, or removing La, increases the density of empty states at the top of the valence band and bottom of the conduction band, increasing the intensity of these transitions. This approach for studying solid solution behavior can be extended to other systems in the future, and the fundamental understanding of the origins of absorption also enables its in situ use as a quantitative probe of thin film point defect concentrations and kinetics.

中文翻译：

非稀氧化物固溶体中光吸收的起源和控制：Sr（Ti，Fe）O _{3– x}钙钛矿的案例研究

理解并合理地调整非稀释氧化物固溶体的缺陷介导的光吸收是一个复杂的挑战。在这项工作中，我们研究了SrTiO ₃ -SrFeO _2.5固溶体中的成分，这与简单的稀铁取代SrTiO ₃情况不同。通过异地和原地通过脉冲激光沉积并通过密度泛函理论模拟制备的混合导电薄膜的光吸收测量，我们证明了对光吸收行为的理解和合理定制。实验上，宽的亚隙吸收峰集中在2.1和2.8–3 eV附近，其强度随Fe和/或O浓度的增加而增加，随La供体掺杂物浓度的增加而降低。与这些观察结果一致，在完全氧化的条件下发现吸收与空穴浓度和Fe浓度成正比。此行为与稀释情况相似。然而，固溶体的电子结构和光吸收行为不能简单地用刚性带模型中的费米能级位移来表示。模拟证实了这些趋势，并确定了在价带内从混合态（O 2p / Fe 3d）价带最大值到空态以及在杂化（Ti / Fe 3d）导带最小态的空态引起吸收的跃迁。添加氧或铁，或除去La，会增加价带顶部和导带底部的空态密度，从而增加这些跃迁的强度。这种用于研究固溶体行为的方法可以在将来扩展到其他系统，并且对吸收起源的基本理解也使其能够添加氧或铁，或除去La，会增加价带顶部和导带底部的空态密度，从而增加这些跃迁的强度。这种用于研究固溶体行为的方法可以在将来扩展到其他系统，并且对吸收起源的基本理解也使其能够添加氧或铁，或除去La，会增加价带顶部和导带底部的空态密度，从而增加这些跃迁的强度。这种用于研究固溶体行为的方法可以在将来扩展到其他系统，并且对吸收源的基本理解也使其能够原位用作薄膜点缺陷浓度和动力学的定量探针。

更新日期：2019-01-10

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