The BaCeO3-based composite protonic conductors prepared by Spark Plasma Sintering (SPS) and free-sintering methods

Abstract

The poor chemical stability and unsatisfactory electrical conductivity of the BaCeO3-based protonic conductors may be improved by doping, by the creation of solid solutions (e.g. with BaZrO3) or by the formation of composite materials. In this work, the latter approach was used and the BaCe0·9Y0·1O3 – (Ba–Ce–Y–Si–P–O) composites were synthesized and investigated. The BaCe0·9Y0·1O3 host material and the modifier phase (6 wt%) powders were mixed by mechanical homogenization. The sintering of compacted powders was done using Spark Plasma Sintering (SPS) and the free-sintering (FS) methods, followed by the post-annealing of some samples. The influence of the sintering method and the presence of the modifier phase on the phase composition, crystallographic structure, microstructure and electrical properties were investigated. A strong influence of the sintering method on these properties was found. Also, the introduction of the modifier phase leads to considerable changes in phase composition, which are dependent on the sintering method and the post-annealing treatment. The electrical properties, determined in different gas atmospheres using the Electrochemical Impedance Spectroscopy (EIS) technique, were correlated with the phase composition and microstructure changes. The minor increase of electrical conductivity due to the introduction of the modifier phase was observed only in the case of SPS sintered samples. A detailed discussion of the observed correlations including the possible chemical composition and structural changes, mutual reactivity, amorphization, the removal of residual stress and the detailed analysis of the EIS results was done. The formation of BaCe0·9Y0·1O3 – (Ba–Ce–Y–Si–P–O) composite materials using the Spark Plasma Sintering method was found to be a promising approach towards ceramic protonic conductors with improved properties.