High temperature characterization of piezoelectric lithium niobate using electrochemical impedance spectroscopy resonance method

Piezoelectric materials reversibly deform when exposed to an electric field. This property is indispensable to modern engineering devices, enabling a wide range of sensors and actuators. However, unfortunately conventional piezoelectric materials are limited to operating temperatures of below approximately 200 °C. Lithium niobate is a promising candidate for high temperature applications (above 500 °C), as it has a high Curie temperature (1200 °C) and good piezoelectric properties. Nevertheless, degradation mechanisms occurring at elevated temperatures are not fully understood, although they are known to interfere with the piezoelectric behavior. In addition, the material properties of this technologically promising ceramic have not been adequately characterized at high temperatures, particularly when excited at high frequencies, due to the difficulty of performing such measurements. We therefore employ an electrochemical impedance spectroscopy resonance method using a novel analytical model to determine the material properties of single crystal lithium niobate over the wide frequency range of 100 kHz to 7 MHz for temperatures up to 750 °C. We find that lithium niobate retains its good piezoelectric properties over this entire frequency and temperature range and rules out suspected degradation mechanisms involving ionic conductivity or vacancy diffusion.