Effect of Chemical Inhomogeneity on the Dielectric and Impedance Behaviors of Bismuth Sodium Titanate Based Relaxors

Abstract

Different levels of Nb2O5 substitution in 0.66(Bi0.5Na0.5)TiO3−0.06BaTiO3−0.28(Bi0.2Sr0.7)TiO3 (BS-xNb) lead-free relaxors were prepared to investigate the effect of chemical heterogeneity on the dielectric and impedance behaviors. X-ray diffraction reveals that the secondary phase gradually increases in number and intensity as the dopant increases. The substitution of less Nb5+ for Ti4+ leads to reduced electronic conductivity and dielectric loss, which is attributed to the inhibition of oxygen vacancies and associated electron. It is found that more valence electron defects are generated to cause charge leakage by introducing excess Nb2O5. Moreover, the addition of Nb2O5 doping enhances the disorder and facilitates the transition of the nonergodic to ergodic relaxor phase. The ferroelectric ergodic long-range order is further disrupted and promotes the formation of local defect fields and high-temperature polar nanoregions. These effects enhance the relaxation behavior with decreased remnant polarization and form a broadly flat dielectric platform. Meanwhile, BS-2Nb exhibits attractively high recoverable energy storage density and efficiency at a relatively low electric field with stability against frequency and temperature. Combined with the complex impedance characteristics, the leakage contribution of the chemical inhomogeneity introduced by excess Nb2O5 is presented, demonstrating the significance of regulating the dielectric performance of bismuth sodium titanate-based relaxors.