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

压电式传感器在监测恶劣环境中的工业过程(如能量转换)和提高效率方面具有很大的应用前景。无线侦察系统的应用为其巨大的经济意义提供了支持。为了准确确定相关器件的工作频率，要求具有低的机电损耗以及在极端温度下的高稳定性。因此，研究、了解和最小化压电晶体中的机电损耗效应是关键目标。在最初的应用中选择压电CTGs(Ca3TaGa3Si2O14)晶体是合理的，因为在本报告所述期间证实了它具有非常低的机电损耗。从确定共振频率的热膨胀、导热系数和与温度的关系以及声波的特征相速度等基本性质入手，详细研究了1000℃以下的原子输运机制。建立了反映主导原子输运机制的缺陷模型。此外，还获得了4.2K到900°C极宽温度范围内的全套机电材料常数，从而可以进行器件模拟。机电损耗是与国家标准和技术研究所一起详细确定的，并在分配基本损耗机制的模型框架中进行描述。总而言之，CTGs在1000°C下表现出非常低的损耗和非常好的长期稳定性，这突显了它与高温系统的相关性。基于第一个资助期的研究结果，在低氧分压下的原子输运、质子和/或羟基对电荷输运的贡献、点缺陷对机电损耗的贡献、非线性压电系数对机电器件行为的影响以及表面和体声波衰减的极化相关性方面都存在悬而未决的问题。将再次根据申请者的互补能力对从目标得出的一揽子工作进行调查，同时考虑到从室温到TU Clausthal的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。为了识别缺陷，利沃夫国立理工大学还将测量光吸收。Leibniz IFW Dresden的主要研究将包括随温度变化的BAW和增加频率范围的声表面波衰减的研究、粘度张量和特定声表面波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.