Langasite based high-temperature bulk acoustic wave sensors

The objective of the work is to review the high-temperature properties, the operation limits and the sensor principles related to high-temperature stable langasite (La₃Ga₅SiO₁₄, LGS) resonators. The electromechanical properties of such resonators including mechanical stiffness, piezoelectric and dielectric constant, effective viscosity and electrical conductivity are determined up to 900°C and described using a one-dimensional physical model. Insights from defect chemical models are correlated with the electromechanical properties of the resonators. Further, application examples are given which demonstrate the capabilities of high-temperature stable piezoelectric resonators. For example, the simultaneous determination of mechanical and electrical properties of thin sensor films by resonant sensors enables the detection of CO in hydrogen-containing atmospheres. Further, the ability of langasite resonators to detect soot at elevated temperatures is demonstrated.