Defect chemistry and electromechanical properties of piezoelectric Ca3TaGa3Si2O14 single crystals at extreme temperatures

压电传感器在恶劣环境下监测工业过程（例如用于能量转换）并提高其效率方面非常有前途。无线询问系统的应用支持了巨大的经济重要性。为了准确确定相关器件的工作频率，需要在极端温度下具有低机电损耗和高稳定性。因此，研究、理解和最小化压电晶体中的机电损耗效应是关键目标。在初始应用中选择压电CTGS（Ca 3 TaGa 3Si 2 O 14）晶体是合理的，因为它具有非常低的机电损耗，这在报告期间得到了证实。从确定基本属性，如热膨胀，热导率和谐振频率的温度依赖性以及声波的特征相速度开始，在高达1000°C的温度下进行原子输运机制的详细研究。一个缺陷模型，反映占主导地位的原子输运机制的发展。此外，获得了从4.2 K到900°C的极宽温度范围内的完整机电材料常数，允许器件模拟。机电损失是与美国国家标准与技术研究所一起详细确定的，并在分配基本损失机制的模型框架中描述。总之，CTGS在1000°C下表现出非常低的损耗和非常好的长期稳定性，这突出了其与高温系统的相关性。根据第一个资助期内获得的结果，在低氧分压下的原子输运、质子和/或OH-基团对电荷输运的贡献、点缺陷对机电损耗的贡献、非线性压电系数对机电装置的行为的影响，以及表面和体声波衰减的偏振依赖性。根据申请人的互补能力，考虑到TU Clausthal在室温至1300°C范围内缺陷化学，原子输运和机电损耗之间关系的新方面，将再次研究这些目标的工作包。为了识别缺陷，将在利沃夫国立理工大学额外测量光吸收。Leibniz IFW Dresden的主要研究将包括对增加的频率范围内的温度相关BAW和SAW阻尼的研究，粘度张量和特定SAW参数的确定以及非线性压电行为。

Piezoelectric sensors are very promising for monitoring industrial processes in harsh environments (e.g. for energy conversion) and increasing their efficiency. The great economic importance is supported by application of systems with wireless interrogation. To exactly determine the operating frequency of related devices, low electromechanical loss as well as high stability at extreme temperatures are required. Consequently, investigation, understanding and minimization of electromechanical loss effects in piezoelectric crystals are key objectives.The choice of piezoelectric CTGS (Ca3TaGa3Si2O14) crystals made in the initial application is justified since it exhibits very low electromechanical loss as confirmed during the reporting period. Starting from the determination of fundamental properties such as thermal expansion, thermal conductivity and temperature dependence of the resonance frequency as well as of characteristic phase velocities of acoustic waves, a detailed investigation of the atomic transport mechanisms at temperatures up to 1000°C are carried out. A defect model reflecting the dominant atomic transport mechanism is developed. Furthermore, the complete set of electromechanical material constants in an extremely wide temperature range from 4.2 K to 900°C is obtained, allowing device simulations. The electromechanical loss is determined in detail together with the National Institute of Standards and Technology and described in the frame of a model that assigns the fundamental loss mechanisms. In conclusion, CTGS shows very low loss and very good long-term stability at 1000°C, which underlines its relevance for high-temperature systems.Based on the results obtained during the first funding period, there are open questions in the field of atomic transport at low oxygen partial pressures, the contribution of protons and/or OH- groups to the charge transport, the contribution of point defects to electromechanical loss, the influence of non-linear piezoelectric coefficients on the behavior of electromechanical devices as well as in the polarization dependence of attenuation of surface and bulk acoustic waves. The work packages derived from the objectives will again be investigated according to the complementary competencies of the applicants, taking into account new aspects of the relationship between defect chemistry, atomic transport and electromechanical loss in the range from room temperature to 1300°C at TU Clausthal. For the identification of defects, the optical absorption will be measured additionally at the Lviv National Polytechnic University. The main research at Leibniz IFW Dresden will include the investigation of temperature dependent BAW and SAW damping for an increased frequency range, the determination of the viscosity tensor and of specific SAW parameters as well as the non-linear piezoelectric behavior.