Hydration and conduction behavior of Sc and Zr-substituted Ba7Nb4MoO20

Ba 7 Nb 4 MoO 20 has acceptably high ionic conductivity at 600–800 °C and is attractive for potential application in high temperature solid state electrochemical devices. Up to now, most of the research focuses on isovalent and donor-doping to improve the electrical properties of Ba 7 Nb 4 MoO 20 . In this work, an acceptor-doping strategy was taken by doping Sc and Zr to partially substitute Nb. More vacant oxygen sites thereby form for charge compensation, leading to the increasing proton concentration following the compositional sequence of hydrated Ba 7 Nb 4 MoO 20  < Ba 7 Nb 3.97 Zr 0.03 MoO 19.985  < Ba 7 Nb 3.97 Sc 0.03 MoO 19.97 . Notably, both the H 2 O/D 2 O isotope effect and EMF measurements indicate that the proton conduction – if there is any – is negligibly small, and the Sc and Zr-doped Ba 7 Nb 4 MoO 20 is essentially an oxide ion conductor in the temperature range studied in this work.