Local Order and Oxygen Ion Conduction Induced High-Temperature Colossal Permittivity in Lead-Free Bi_0.5Na_0.5TiO₃-Based Systems

In this study, an effective method is presented to enhance the dielectric constant at high temperature through Ba2+, Mg2+ codoped nonstoichiometric Bi0.5Na0.5TiO3 (BNT) relaxor ferroelectric ceramics. The temperature dependence of permittivity, complex impedance spectrum, and conductivity was investigated to understand the effect of Ba2+, Mg2+ doping on dielectric properties of BNT. The results show that the value of dielectric constant of (Ba0.01Bi0.5Na0.49)(Ti0.9Mg0.1)O3 ceramics increases 2 orders of magnitude with a very broad temperature range corresponding to pure BNT ceramics. The results of conductivity and complex impedance spectrum with various temperatures indicate that the high-temperature dielectric constant is mainly caused by oxygen ion conductivity and the interfacial effect. The A-site local order induced by Ba2+ doping generates dielectric anomalies, which results in the broadening temperature range for colossal dielectric constant. The study provides a new method to obtain a colossal dielectric constant system with a wide temperature range.