Synthesis and characterization of high temperature proton conductors of type Ba3Ca1+xNb2−xO9−δ

High temperature proton conductors (HTPCs) of composition Ba3Ca1+xNb2−xO9 have recently attracted considerable interest for possible applications in sensors, fuel cells etc. We give here a preliminary account of the synthesis of compounds with x=−0.03, 0.0, 0.12, 0.18 and 0.35. Both, the oxide and the sol-gel route were successfully used. Calcination and densification were systematically investigated supported by particle size measurements. The resulting samples were characterized using a) x-ray techniques for structural details, b) TEM techniques to search for domain boundaries and foreign phases, c) density measurements to check the results of various densification procedures and d) temperature programmed desorption (TPD) to elucidate the evolution of gases with temperature. The thermal expansion coefficient was determined in selected cases and dilatometry was used to determine the temperature range in which the density saturates.