The effect of A-site sublattice order on the electrical properties of Na_0.5Bi_0.5TiO₃ compound

The A-site sublattice order of the Na_0.5Bi_0.46K_0.04TiO_2.96 (NBT-K4) compound was changed by the isovalent Na⁺ ions partly substituting K⁺ ions. The Na_0.5+xBi_0.46K_0.04−xTiO_2.96 (x = 0, 0.01 and 0.02) samples were prepared. By the AC impedance test, the grain conductivity of the Na_0.52Bi_0.46K_0.02TiO_2.96 (x = 0.02) samples is 8.23 × 10⁻⁴ S/cm at 623 K, which is around 1.65 times higher than that of NBT-K4 sample at the same tested temperature. By anatomizing relaxation spectroscopy, when the Na-doped content x in the NBT-K4 compound increases from 0 to 2 mol%, the activation energy E decreases from 0.64 to 0.57 eV. Accompany with the rise of the Na-doped content in the NBT-K4 compound, although the mobile oxygen vacancy content decreases, the oxygen vacancy diffusivity are strengthened. The higher oxygen vacancy jumping rates and lower oxygen relaxation activation energies were found in the Na-doped NBT-K4 samples, which causes the higher grain conductivity in the Na_0.5+xBi_0.46K_0.04−xTiO_2.96 (x = 0.01 and 0.02) samples. There is the higher oxygen-ion conductivity and lower activation energy in the relative A-site order of Na-doped NBT-K4 compound, which is consistent with the first principle simulation results. The investigation provides a new way to design a high oxygen-ion conductivity NBT-based oxide ion conductors and related materials.