Influence of the La6W2O15 Phase on the Properties and Integrity of La6-xWO12-?–Based Membranes

The aim of the present work is to evaluate the influence of La6W2O15 secondary phase on the properties and integrity of La6-xWO12-δ–based membranes. Structural, microstructural and thermo–chemical study was carried out evidencing significant crystallographic and thermal expansion anisotropy: the reason for poor thermo–mechanical stability of La6W2O15. Conductivity of La6W2O15 was one to two orders of magnitude lower compared to the phase pure La6-xWO12-δ in the range of 300 to 900 °C. The relaxation study showed that the hydration process was faster for the La6W2O15 compared to the LWO phase, due to the higher electronic contribution to the total conductivity. Short–term stability tests in H2 at 900 °C and in a mixture of CO2 and CH4 at 750 °C were conducted and material remained stable. Remarkable reactivity with NiO and YSZ at elevated temperatures was further evidenced compared to the relative inert behavior towards MgO and CGO.