Chemical expansion of praseodymium-cerium mixed oxide films at high temperatures

该研究项目的主要目标是研究薄膜在高温下的化学膨胀。待研究的材料是镨铈混合氧化物（PCO），温度范围为400 ° C至700 ° C。与例如高温压电晶体相比，该选择的动机是在插入或移除氧时显著更高的机械膨胀。与块体材料相比，PCO膜提供了低时间常数的优点，因为氧气的传输距离短。除了化学膨胀，层中的缺陷结构和决定时间的原子输运机制必须确定。开发、实现和测试一种特殊的干涉仪或更准确地说是振动计是一项重要的技术任务，该干涉仪甚至能够在几毫赫兹的频率下测量亚纳米范围内的层厚度变化。通过差分振动计的开发和信号分集的使用，信号的噪声应该大大降低。研究结果和新的测量方法可以应用于PCO模型系统以外的其他材料，从而可以进一步了解其他力学系统中的化学膨胀和小位移。然而，几乎没有任何关于薄膜化学膨胀的数据。它们在很大程度上是间接确定的，并显示出一些矛盾。与结构材料和电子功能材料相比，高温致动器材料需要广泛的研究。这种高温"人造肌肉"是能源转换和太空探索等领域所需要的。申请人在高温材料领域和振动计开发领域具有互补能力，非常适合解决科学挑战，并且在这种组合中是独一无二的。此外，这项工作将与一位作者密切合作进行，这位作者显然是唯一一位关于PCO膜膨胀的机械测定的出版物的作者，因此计划的样品交换提供了可比的结果。初步工作表明，振动计通常能够检测由电化学泵送氧气引起的PCO膜厚度的变化。然而，一个重要的限制是标准振动计在低频时的信号噪声。PCO薄膜中的氧平衡需要几毫赫兹的激发频率，到目前为止还没有有意义的测量。例如，在仪器方面，已经表明信号分集显著降低了噪声。

The primary objective of the research project is to investigate the chemical expansion of thin films at high temperatures. The material to be studied is praseodymium-cerium mixed oxide (PCO) in the temperature range from 400 °C to 700 °C. The choice is motivated by considerably higher mechanical expansion upon insertion or removal of oxygen in comparison to e.g. high-temperature piezoelectric crystals. Compared to bulk material, PCO films offer the advantage of low time constants as short transport distances for oxygen occur. In addition to the chemical expansion, the defect structure in the layers and the time-determining atomic transport mechanisms have to be determined. The development, realization and test of a special interferometer or more precisely vibrometer, which is able to measure changes of the layer thickness in the sub-nanometer range even at frequencies of a few millihertz, represents an essential technical task. Through the development of a differential vibrometer and the use of signal diversity, the noise of the signal should be drastically reduced. The results and the new measuring method can be applied to other materials than the PCO model system, so that further insights into chemical expansion and small displacements in other mechanical systems can be obtained.The topic is highly relevant. However, hardly any data on the chemical expansion of thin films is available. They have been determined largely indirectly and show some contradictions. In contrast to structural materials and electronic functional materials, high-temperature actuator materials require extensive research. Such high temperature "artificial muscles" are e.g. demanded for energy conversion and space exploration.The applicants have complementary competences in the field of high-temperature materials and the development of vibrometers, which are well suited for solving the scientific challenge and which are unique in this combination. Furthermore, the work will be carried out in close cooperation with an author of the apparently only available publication on mechanical determination of PCO film expansion, so that the planned sample exchange provides comparable results.The preliminary work has shown that vibrometers are generally able to detect changes in the thickness of PCO films which are caused by electrochemical pumping of oxygen. A significant restriction, however, is the signal noise of standard vibrometers at low frequencies. Oxygen-equilibrium in the PCO films requires excitation frequencies of a few millihertz, where no meaningful measurements are possible so far. On the instrumentation side, for example, it has been shown that signal diversity significantly reduces noise.