Enhanced sinterability of Ba3MoNb0.95Zr0.05O8.475 oxide ion conductor by adding K2CO3

Ba 3 MoNbO 8.5 -based materials are an attractive class of hexagonal perovskite-derived oxide ion conductors, and the oxide ion conductivity can be increased to 0.012 Scm −1 at 700 °C by doping Zr to form the composition of Ba 3 MoNb 0.95 Zr 0.05 O 8.475 (BMNZ5). However, BMNZ5 shows lower relative density around 69% after sintering at 1200 °C. Increasing the temperature to 1300 °C densifies the sample but unfortunately results in the formation of a BaMoO 4 second phase. Interestingly, adding K 2 CO 3 leads to the reduced temperature forming the BMNZ5 phase, and the relative density increases to 89% by adding 5 mol% K 2 CO 3 . Although the conductivity decreases slightly, adding K 2 CO 3 leads to an acceptable balance between the relative density and conductivity. The samples added with 1.0, 2.5 and 5.0 mol% K 2 CO 3 show reasonably high total conductivity of 0.0079, 0.0062 and 0.0077 Scm −1 at 700 °C in a dry Ar-20% O 2 atmosphere. No proton conduction was detected in both the pristine and 2.5 mol% K 2 CO 3 -added compositions by the H 2 O/D 2 O isotope effect measurements.