Structural and microstructural correlation with ferroelectric and dielectric properties of nanostructured Na0.5Bi0.5TiO3 ceramics

Polycrystalline Na0.5Bi0.5TiO3 (NBT) ceramics were synthesized by using sol–gel and solid state reaction techniques with an average grain size of ≅240 nm and ≅14 μm respectively. Structural analysis confirmed the R3c phase-stabilization in both bulk and nano-NBT. The lattice strain analysis estimated by using W–H plot from the XRD profiles revealed the strain was compressive in NBT-nano. Phonon life times (τ) of Na/Bi–O, Ti–O and TiO6 phonon modes were decreased in NBT-nano due to the grain size effect. Microstructure of NBT-nano displayed an enormous rise in the number of grain boundaries than NBT-bulk. Ferroelectric loops became slanted in NBT-nano due to the multi-domain to mono-domain transformation. The mono-domain transition eased the domain reversal and switching, which in-turn lowered the Ec value in NBT-nano (i.e. Ec = 45 kV/cm). The clamping effect caused by grain size reduction in NBT-nano leads to reduced Pr value (Pr = 25.2 µC/cm2). The compressive strain developed in the crystal lattice of NBT-nano leads to an increase in Tm (i.e. 335 °C). The variation in diffusivity parameter (γ) and degree of correlation strength q(T) between the polar nano regions were found to be the cause for enhanced relaxor features in NBT-nano.