Inter-growth bismuth layer-structured ferroelectdcs (BLSFs),Bi4Ti3Ol2-Na0.5Bi4.5Ti4O15 (BIT-NBT),were successfully synthesized using the traditional solid-state reaction method.X-ray diffraction (XRD) Rietveld refinements were conducted using GSAS software.Good agreement and low residual are obtained.The XRD diffraction peaks can be well indexed into I2cm space group.The inter-growth structure was further observed in the high-resolution TEM image.Dielectric and impedance properties were measured and systematically analyzed.At the temperature range 763-923 K (below Tc),doubly ionized oxygen vacancies (OVs) are localized and the short-range hopping leads to the relaxation processes with an activation energy of 0.79-1.01 eV.Above Tc,the doubly charged OVs are delocalized and become free ones,which contribute to the long-range dc conduction.The reduction in relaxation species gives rise to a higher relaxation activation energy ～ 1.6 eV.