WEB Electrical and Electromechanical Properties of Single Crystalline Lithium Niobate-Tantalate Solid Solutions at Elevated TemperaturesTuesday (22.09.2020) 12:05 - 12:20 F: Functional Materials, Surfaces, and Devices 2 Part of:
Piezoelectric materials with sufficiently high piezoelectric coefficients that can be operated at temperatures considerably above 500 °C are in high demand for industrial actuating applications. Lithium niobate (LiNbO3, LN) and lithium tantalate (LiTaO3, LT) possess high piezoelectric coefficients, however their usage is limited by thermal instability (LN) and low Curie temperature (LT). In this respect Li(Nb,Ta)O3 (LNT) solid solutions are expected to overcome the above-mentioned restrictions of the individual compounds. The current work focuses on the electrical and electromechanical properties of LNT solid solutions with different Nb/Ta ratios at high temperatures and in a wide oxygen partial pressure (pO2) range. Further, the transport mechanisms in LNT at elevated temperatures are studied as well. The bulk crystals for the study are grown by two different methods namely micro-pulling-down and Czochralski techniques. The electrical and electromechanical properties are investigated by means of impedance spectroscopy and resonant ultrasound spectroscopy, respectively. The oxygen transport kinetics are investigated in the temperature range from 850°C to 1200°C using the 18O isotope as the tracer. Subsequently, the diffusion profiles are acquired by secondary ion mass spectrometry. The high-temperature experiments are performed on platinum-electroded samples in a gas-tight tube furnace, which allows working temperatures up to 1000 °C. The adjustment of pO2 is realized using an oxygen ion pump in the range from 10^-15 to 10^-3 bar by well-defined Ar/H2/O2 gas mixtures. The investigations revealed, that LNT solid solutions show considerably lower conductivity than LiNbO3 at high temperatures and low oxygen partial pressures, which implies improved stability. At 930 °C and pO2 = 10^-15 bar, the electrical conductivity of LiNb0.29Ta0.71O3 sample is almost two orders of magnitude lower than that of LiNbO3.