The investigation of the defect chemistry of solid oxides is of central importance for the understanding of redox processes. This can be performed by measuring conductivity as a function of the oxygen partial pressure, which is conventionally established by using buffer gas mixtures or oxygen pumps based on zirconia. However, this approach has some limitations, such as difficulty in regulating oxygen partial pressure in some intermediate-pressure regions or the possibility of influencing the redox process by gases that can also be incorporated into the oxide or react with the surface via heterogeneous catalysis. Herein, we present an alternative physical method in which the oxygen partial pressure is controlled by dosing pure oxygen inside an ultra-high vacuum chamber. To monitor the conductivity of the oxide under investigation, we employ a dedicated four-probe measurement system that relies on the application of a very small AC voltage, in combination with lock-in data acquisition using highly sensitive electrometers, minimizing the electrochemical polarization or electro-reduction and degradation effects. By analyzing the model material SrTiO₃, we demonstrate that its characteristic redox behavior can be reproduced in good agreement with the theory when performing simultaneous electrical conductivity relaxation and high-temperature equilibrium conductivity measurements. We show that the use of pure oxygen allows for a direct analysis of the characteristic oxygen dose, which opens up various perspectives for a detailed analysis of the surface chemistry of redox processes.

中文翻译：

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研究固体金属氧化物中缺陷化学的物理方法

固体氧化物缺陷化学的研究对于理解氧化还原过程至关重要。这可以通过测量作为氧分压的函数的电导率来执行，这通常是使用缓冲气体混合物或基于氧化锆的氧气泵来建立的。然而，这种方法具有一些局限性，例如难以在某些中压区域中调节氧分压或可能通过也可以混入氧化物或通过非均相催化与表面反应的气体影响氧化还原过程的可能性。在这里，我们提出了一种替代的物理方法，其中通过在超高真空室内计量纯氧来控制氧分压。为了监控所研究的氧化物的电导率，我们采用专用的四探针测量系统，该系统依赖于非常小的交流电压的施加，并结合使用高灵敏静电计的锁定数据采集，从而最大程度地减少了电化学极化或电还原和降解效应。通过分析模型材料SrTiO_{如图3所示}，当同时进行电导率松弛和高温平衡电导率测量时，我们证明其特征性的氧化还原行为可以与理论很好地重现。我们表明使用纯氧可以直接分析特征氧的剂量，这为氧化还原过程的表面化学的详细分析开辟了各种前景。