Development of high-temperature stable piezoelectric materials and electrodes

在高达1300°C的温度范围内，压电材料的电损耗和电极的稳定性被我们的团队确定为压电器件的限制因素。由于温度的限制，高吸引力的传感器和执行器应用是不可行的。最有前途的高温压电材料是langasite （La3Ga5SiO14）和gaapo4 (GaPO4)，其相稳定性分别高达约1470°C和930°C。我们小组目前正在研究langasite的高温特性。因此，本文研究的重点是后一种材料。尽管温度限制为930°C，但在高达900°C的温度下，正磷酸镓的极低电损耗证明了研究的合理性。项目的第一部分包括对压电行为的研究，在运行过程中微观结构和成分的变化以及它们与晶体生长条件的关系。谐振装置的电极经历极高的加速度。它们必须在高导电性和低质量之间取得良好的折衷。力学性能必须几乎与气体气氛和温度无关，以避免共振行为的干扰。因此，谐振器件对电极的要求超过了普通高温电极。因此，该项目的第二部分的目标是研究和改进电极性能，包括化学和热稳定性，电导率，粘接强度以及电极氧化和非化学计量学，温度范围高达1300°C。建议起始材料为Pt-Rh合金、TiN和La0.3Sr0.7CrO3。

Electrical losses in piezoelectric materials and the stability of the electrodes were identified by our group as the limiting factors of piezoelectric devices in the temperature range up to 1300 °C. Highly attractive sensor and actuator applications are not feasible due to temperature limitations. The most promising high temperature piezoelectric materials are langasite (La3Ga5SiO14) and gallium orthophosphate (GaPO4) exhibiting a phase stability up to about 1470 °C and 930 °C, respectively. Our group is presently investigating the high temperature properties of langasite. Therefore, the emphasis of the proposed research is on the latter material. Despite the temperature limit of 930 °C, the study of gallium orthophosphate is justified by the extremely low electrical losses at temperatures up to 900 °C. The first part of the project includes the investigation of the piezoelectric behavior, of the microstructural and compositional changes during operation and of their correlation with the crystal growth conditions. The electrodes of resonant devices experience extremely high accelerations. They must represent a good compromise on high conductivity and low mass. The mechanical properties must be nearly gas atmosphere and temperature independent to avoid disturbances of the resonance behavior. Consequently, the demands on electrodes for resonant devices exceed those for common high temperature electrodes. Therefore, the objective of the second part of the project is the investigation and improvement of the electrode properties including chemical and thermal stability, electrical conductivity, adhesive strength as well as electrode oxidation and non-stoichiometry in the temperature range up to 1300 °C. Proposed starting materials are Pt-Rh alloys, TiN and La0.3Sr0.7CrO3.