Low temperature sintering of LaNbO4 proton conductors from freeze-dried precursors

A synthesis method based on freeze-dried precursors was used to obtain nanocrystalline powders of pure and Ca-doped LaNbO4 at 800°C. Dense ceramics were prepared at temperature as low as 1100°C. The LaNbO4 ceramics were examined by scanning electron microscopy (SEM) to study the microstructure evolution with the sintering temperature. The densification and grain growth rate are lower in Ca-doped samples. The bulk and grain boundary contributions to the overall conductivity were studied by impedance spectroscopy under different gases. Samples sintered at low temperature and with smaller grain size exhibit higher grain boundary resistance and consequently lower total conductivity.