High-Temperature Electrical Conductivity and Electro- mechanical Properties of Stoichiometric Lithium Niobate

High temperature properties such as electrical conductivity (σ) and reson- ance behaviour of stoichiometric lithium niobate (LiNbO3) are determined in the tempera- ture range from 20 to 950 °C. The activation energy of the conductivity is found to be 0.9 and 1.7 eV in the temperature range from 500 to 750 °C and from 800 to 950 °C, respec- tively. During thermal treatments in ambient air up to 950 °C and back, the conductivity remains unchanged at a given temperature, i.e., the crystal is stable under these condi- tions. The oxygen partial pressure (pO2) dependence of the conductivity shows two dis- tinct ranges. At 750 °C, the property remains unchanged down to 10 −15 bar. Below 10 −15 bar, the conductivity increases according to σ ~ (pO2) −1/5 . Z-cut LiNbO3 plates can be excited to thickness mode vibrations up to at least 900 °C. At this temperature, the quality factor Q is found to be between 30 and 100. As for changes of the conductivity, a de- crease of the resonance frequency is observed below 10 −15 bar indicating a correlation of both properties. In order to evaluate the lithium evaporation, the crystals are tempered at 900 °C in ambient air for 24 h. A depth profile of the constituents does not indicate li- thium loss within the accuracy of the secondary ion mass spectroscopy. The preliminary results underline the potential of stoichiometric LiNbO3 for high-temperature applications and justify its closer investigation.