Dynamic Piezoelectric Behavior of Lithium Niobate at High Temperature

Abstract

High temperature piezoelectric materials have numerous potential applications, including high temperature ultrasound NDT, MEMS, sensors, or actuators. However, conventional piezoelectric materials are unsuitable for operation above 400°C. Lithium niobate (LiNbO3) is a promising candidate because of its very high Curie temperature (approximately 1210°C) and reasonable piezoelectric coefficients. However, the piezoelectric properties are not sufficiently understood, partly due to the difficulties in characterizing this behavior at high temperature. Degradation mechanisms well below the Curie temperature, suspected to include phase transformations, oxygen loss, and excessive ionic conductivity, further deteriorate this property. In order to better understand these physical mechanisms, electrochemical impedance spectroscopy (EIS) is used to characterize monocrystalline LiNbO3 from room temperature to 500°C, with excitations from 20 Hz to 20 MHz. An equivalent circuit model analysis, including resonant frequencies, is developed to investigate the temperature dependence of the piezoelectric behavior, as well as the mechanical elasticity and damping. Numerical values extracted from this analysis allows for numerical simulations to model device behavior.