Origin of anomalous giant dielectric performance in novel perovskite: Bi(0.5-x)LaxNa(0.5-x)LixTi(1-y)MyO3 (M = Mg2+, Ga3+).

Dielectric properties and dielectric relaxation behaviors of A/B sites co-substituted Bi0.5Na0.5TiO3 perovskite-type ferroelectrics are reported. The Bi(0.5-x)LaxNa(0.5-x)LixTi(1-y)MyO3 (M = Mg(2+), Ga(3+)) exhibits anomalous giant dielectric permittivity (ε') of ~10(5) under a heterogeneous constitution with easily discernible grain and grain boundary conductivity. The lone pairs substitution theory as well as extrinsic disorders are used to clarify the significant structural evolution and the origin of the dielectric performance. A bigger free volume promotes the anomalous relaxation between oxygen sites, and the polarization direction on the nanoscale deviates from the average polarization direction at its ferroelectric state. Furthermore, no obvious phase transition indicates the considerable static substitutional disorder at the Bi/Na sites, which facilitates delocalized conduction of oxygen ions in the intermediate temperature range.