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

• Applicant: Professor Dr.-Ing. Holger Fritze
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 409656768

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.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research
• Cooperation Partner: Professor Dr. Dmitry Roshchupkin