Peculiarities of the synthesis of lithium ion conducting lanthanum tantalate by solid-state reaction and precipitation from solutions

Synthesis of lithium ion conducting tantalates has been carried out by conventional solid-state reaction (SSR) techniques and by precipitation from solutions (PS). It is shown that the latter chemical route leads to the formation of a pure perovskite phase, made up of nanosized particles, and uses milder conditions when compared with the solid-state reaction technique. Thermal analyses, X-ray powder diffraction (XRD) and infrared (IR) spectroscopy are used to investigate the phase transformations that occur during the preparation of these tantalates from powder precursors. After sintering, the nanosized particles of the powder obtained by the (PS) route are preserved and pellets with good compactness (89 %) are obtained. The electrical properties of the sintered ceramics have been investigated by ac impedance spectroscopy. These experiments showed that the total ionic conductivity (bulk and grain boundaries) of the (PS) pellet is slightly lower than that of the (SSR) pellet. This decrease of conductivity is attributed to an enhancement of the blocking effect of the grain boundaries resulting from the microstructure of the fine-grain ceramics. The bulk conductivity is not affected by the synthetic route. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006.