Electrical performance and oxygen relaxation behaviour in Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x compounds were investigated. The oxide ion conductivity of Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x compounds increased first and then decreased with increasing Mg-doped content. The highest oxide ion conductivity of 4.7 × 10 −3 S cm −1 at 773 K was observed for the Na 0.5 Bi 0.5 Ti 0.96 Mg 0.04 O 2.96 compound. A typical relaxation peak in the Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x samples was observed. The activation

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... rgy and pre-exponential factors were determined as (1.0 eV, 4.7 × 10 −16 s) and (0.94−1.0 eV, 6.8 × 10 −14 −3.1 × 10 −13 s) from internal friction and dielectric relaxation measurement, respectively. The lower oxide ion conductivity in Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x (x = 0.06, 0.08, 0.10) compounds may arise from the lower vacancy mobility. Judging from the electrical performance and relaxation parameters, although lower-level Mgdoping can improve oxide ionic conductor, oxygen vacancy mobility in Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x compounds cannot be improved with increasing Mg-doping content. These results will be meaningful to ameliorate the electrical properties of Na 0.5 Bi 0.5 Ti 1−x Mg x O 3−x compounds and understand the relationship between the electrical properties and structure.