Oxygen partial pressure dependent acoustic loss in piezoelectric LiNbO3 resonators at 700 °C

Lithium niobate (LiNbO3) crystals have been the focus of substantial research due to their applications in, for example, optical and surface-acoustic-wave devices at room temperature. Moreover, they are attractive for use as high-temperature resonant sensors or mechanical actuators, where acoustic losses are less significant due to the high piezoelectric coefficients in LiNbO3 compared to non-polar piezoelectric crystals such as quartz or langasite-related compounds. So far, high-temperature charge transport in LiNbO3 has been examined only to a limited extent as a function of oxygen partial pressure ( $$p_{\text{O}_2}$$ ). Furthermore, an explicit correlation between acoustic losses and charge transport at low $$p_{\text{O}_2}$$ has, to the best of our knowledge, not yet been established or published. In this study, the correlation between acoustic losses and electrical conductivity of 3.5 MHz LiNbO3 thickness-shear mode resonators is investigated over a wide $$p_{\text{O}_2}$$ range from 10−20 to 10−4 bar at a temperature of ≈ 700 °C. To describe the losses, a physical model of a vibrating plate is introduced. The key parameter, i.e., the electrical conductivity, is included as measured. The model function is optimized using a least-squares method by varying only the piezoelectric coefficient and the dielectric constant. Good agreement with the data is achieved. Remarkably, the $$p_{\text{O}_2}$$ -dependent conductivity and, therefore, the underlying hopping of small electron polarons govern the overall loss at low $$p_{\text{O}_2}$$ . Furthermore, a $$p_{\text{O}_2}$$ -dependent dielectric constant is required to describe the losses appropriately.