Optimisation of oxide-ion conductivity in acceptor-doped Na0.5Bi0.5TiO3 perovskite: Approaching the limit?

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Abstract

Na0.5Bi0.5TiO3 (NBT) perovskite is often considered as a potential lead-free piezoelectric material but it can also be an excellent oxide-ion conductor (M. Li et al., Nature Materials, 13, 2014, 31-35). Here we report the non-stoichiometry and oxide-ion conductivity of undoped and acceptor-doped NBT. A range of acceptor-type ions with varying doping levels are selected to incorporate into NBT or Bi-deficient NBT (nominal Na0.5Bi0.49TiO2.985; NB0.49T). Low levels of acceptors (typically < 2 at%) can be doped on both cation sites of NBT by an ionic compensation mechanism to create oxygen vacancies and are therefore effective in enhancing the bulk oxide-ion conductivity to values of ∼2 mS cm-1 at 400 °C. A maximum enhancement of less than 1 order of magnitude is achieved using either A-site Sr (or Ca) or B-site Mg doping in NB0.49T. This conductivity maximum is in good agreement with an oxygen-vacancy diffusivity limit model in a perovskite lattice proposed by R. A. De Souza (Advanced Functional Materials, 25, 2015, 6326-6342) and suggests that optimisation of the ionic conductivity in NBT has been achieved. Our findings on NBT illustrate that this approach should be applicable to other acceptor-doped perovskite oxides to determine their electrolyte (oxide-ion) conductivity limit.

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Yang, F., Li, M., Li, L., Wu, P., Pradal-Velázque, E., & Sinclair, D. C. (2017). Optimisation of oxide-ion conductivity in acceptor-doped Na0.5Bi0.5TiO3 perovskite: Approaching the limit? Journal of Materials Chemistry A, 5(41), 21658–21662. https://doi.org/10.1039/c7ta07667c

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