Development of high-temperature stable piezoelectric materials and electrodes

我们小组发现，在1300°C的温度范围内，压电材料的电损耗和电极的稳定性是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。最有希望的高温压电材料是La3Ga5SiO14和GaPO4，它们的相稳定性分别高达1470°C和930°C。我们小组目前正在研究蓝晶石的高温性质。因此，建议研究的重点是后一种材料。尽管温度限制在930°C，但由于在高达900°C的温度下具有极低的电损耗值，因此对正磷酸镓的研究是合理的。该项目的第一部分包括对其压电行为、操作过程中的微观结构和成分变化及其与晶体生长条件的相关性的研究。谐振器的电极经历了极高的加速度。它们必须代表高导电性和低质量的良好折衷。机械性能必须与气体、大气和温度几乎无关，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的要求。因此，项目第二部分的目标是研究和改进电极的性能，包括化学和热稳定性、导电性、结合强度以及在1300°C以下的电极氧化和非化学计量比。建议的起始材料是铂-Rh合金、TiN和La0.3Sr0.7CrO_3。

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.