High proton conductivity in barium yttrium stannate Ba 2YSnO 5.5

Abstract

Ba 2YSnO 5.5 is found to crystallize in a perovskite structure with a=848 pm. The compound may be hydrated (Δ H hydr.°=−101.5 kJ mol −1, Δ S hydr.°=−92.5 J mol −1 K −1) to a high degree (maximum water content=13.5 mol%) which leads to the formation of protonic charge carriers (OH O ⋅) and the occurrence of very high proton conductivity with low activation enthalpy ( E a=0.51 eV) comparable to that of BaCeO 3 based materials which are the oxides with the highest proton conductivities reported so far. The conductivity contributions from native ions (V O ⋅⋅, h ⋅) are found to be negligible for temperatures below 600°C. In contrast to BaCeO 3 based materials Ba 2YSnO 5.5 shows good chemical durability with respect to carbonate formation. However, structural instability becomes apparent in a high grain boundary impedance, a collapse of the structure upon reduction and the macrocracking induced by lattice strain resulting from hydration.