Growth and characterization of single crystalline lithium niobate-tantalate (Li(Nb,Ta)O3) solid solutions for high-temperature sensor and actuator applications

压电传感器由于其在多参数现场监测和过程控制方面的优势而引起了越来越多的关注。特别是，对于适用于高达1000 ° C的温度应用的气体成分、温度和压力的敏感、稳健和具有成本效益的传感器有很高的需求。例如，能量转换、航空航天和其他经济上重要的工业应用（例如，用于涡轮机或太阳能集中器的过程控制的高温注射喷嘴或基于致动器的部件）需要其位移可以通过施加的电压来调节的压电致动器。在任何情况下，都需要同时具有良好的热稳定性和较大的压电系数，而实际应用中常用的压电材料的使用温度受到限制。相关的多晶陶瓷在高于约200 ° C时显示出热不稳定性。硅酸镓镧（La3Ga5SiO14）族的石英晶体虽然在高温下表现出优异的稳定性，但由于其压电系数较低而不适合作驱动器，铌酸锂（LiNbO3）和钽酸锂（LiTaO3）已被认为是高温传感和驱动器件的潜在材料。这两种晶体都具有很高的压电系数，但是它们的使用受到LiNbO3的热不稳定性和LiTaO3的低居里温度的限制。在这方面，Li（Nb，Ta）O3固溶体可能克服上述单个化合物的限制。这一假设得到了我们前期工作的支持。双方研究伙伴的共同目标是开发高温稳定的Li（Nb，Ta）O3固溶体，可应用于传感和驱动应用。这种单晶的生长及其化学和结构表征，包括Nb/Ta比，结构完美性以及线和体缺陷的检查将由俄罗斯合作伙伴实现。此外，该方计划分析声波场，以确定Nb/Ta比对波传播的影响。德国合作伙伴专注于高温性能，从而确定电气和机电性能，研究原子输运并开发缺陷化学模型。将通过稳定示踪同位素18O和6Li进行运输动力学分析，这允许与有关机电损失的数据相一致，以判断高温稳定性。此外，选定的材料常数的Li（Nb，Ta）O3将确定为温度的函数，由两个合作伙伴用不同的方法来验证结果。两个合作伙伴的工作密切相关，应提供关于具有最稳定Nb/Ta比的Li（Nb，Ta）O3的信息，以在第一个项目期间中期为改进晶体的生长提供反馈。

Piezoelectric sensors are attracting increasing interest since they offer numerous advantages for multiparameter in-situ monitoring and process control. In particular, there is a high demand in sensitive, robust and cost-effective sensors for gas composition, temperature and pressure that are suitable for applications at temperatures up to 1000°C. Piezoelectric actuators whose displacement can be adjusted by an applied voltage are required for e.g. energy conversion, aerospace and other economically significant industrial applications such as high-temperature injection nozzles or actuator-based components for process control of turbines or solar concentrators. In any case, excellent thermal stability and large piezoelectric coefficients are required simultaneously.In practice the application temperature of common piezoelectric materials is limited. Related polycrystalline ceramics show thermal instability above about 200°C. Even though quartz type crystals from langasite (La3Ga5SiO14) family show excellent stability at high temperatures, they are not suitable for actuators due to their low piezoelectric coefficients.Lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) have been recognized as potential materials for high-temperature sensing and actuating devices. Both crystals possess high piezoelectric coefficients, however their usage is limited by thermal instability of LiNbO3 and low Curie temperature of LiTaO3. In this respect Li(Nb,Ta)O3 solid solutions possibly overcome the above-mentioned restrictions of the individual compounds. This hypothesis is supported by our preliminary work.The joint objective of both research partners is to develop high-temperature stable Li(Nb,Ta)O3 solid solutions that can be applied in sensing and actuating applications. The growth of such single crystals as well as their chemical and structural characterization, including examination of the Nb/Ta ratio, structure perfection, and line and bulk defects will be realised by the Russian partner. Further, analysis of the acoustic wave fields to determine the influence of Nb/Ta ratio on wave propagation is planned from this party. The German partner focuses on high-temperature properties, thereby determining electrical and electromechanical properties, investigating the atomic transport and developing a defect chemical model. The analysis of transport kinetics will be performed by the stable tracer isotopes 18O and 6Li, which allows in concert with data about electromechanical losses to judge the high-temperature stability. Further, selected material constants of Li(Nb,Ta)O3 will be determined as a function of temperature by both partners with different methods to validate the results. The work of both partners is closely linked and should provide information on Li(Nb,Ta)O3 with the most stable Nb/Ta ratio to provide feedback for growth of improved crystals already in the middle of the first project period.