High temperature properties such as electrical conductivity (σ) and resonance behaviour of stoichiometric LiNbO3 were determined at 20 to 950C. The activation energy of the conductivity was found to be 0.9 and 1.7eV at 500 to 750C and from 800 to 950C, respectively. During thermal treatments in ambient air up to 950C and back, the conductivity remains unchanged at a given temperature, i.e., the crystal was stable under these conditions. The O partial pressure (PO2) dependence of the conductivity shows 2 distinct ranges. At 750C, the property remains unchanged down to 10−15bar. Below 10−15bar, the conductivity increased according to σ ~ (PO2)−1/5. Z-cut LiNbO3 plates could be excited to thickness mode vibrations up to at least 900C. At this temperature, the quality factor Q was found to be between 30 and 100. As for changes of the conductivity, a decrease of the resonance frequency was observed below 10−15bar indicating a correlation of both properties. In order to evaluate the Li evaporation, the crystals were tempered at 900C in ambient air for 24h. A depth profile of the constituents does not indicate Li 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.

High-Temperature Electrical Conductivity and Electromechanical Properties of Stoichiometric Lithium Niobate. G.Ohlendorf, D.Richter, J.Sauerwald, H.Fritze: Diffusion Fundamentals, 2008, 8, 6.1