Analyzing structural changes and variable range hopping conduction in Na0.5Bi0.5TiO3 perovskite: Effect of Sr2+ doping at Bi-site

Abstract

In this present investigation, we explored the impact of Sr²⁺ doping at the Bi-site on the structural, electrical, and optical characteristics of ${\text{Na}}_{0.5}{\text{Bi}}_{0.5}\text{Ti}{O}_3$ (NBT) nanomaterial. By employing the citrate auto-combustion method, we synthesized pure ${\text{Na}}_{0.5}{\text{Bi}}_{0.5}\text{Ti}{O}_3$ nano-perovskites, as well as various Sr-doped counterparts. Analysis of the observed X-ray diffraction patterns through Rietveld refinement revealed a rhombohedral phase with space group R3c, although the composition doped with 10 % Sr exhibited impurity phases. The introduction of Sr²⁺ ions had a discernible influence on diverse microstructural parameters, including lattice parameters (a and c), microstrain, X-ray density, and particle size. Detailed morphological and elemental assessments were conducted utilizing TEM, FE-SEM, and EDX spectroscopy. The analysis of UV–Vis absorption spectra yielded a reduction in the optical band gap with increasing Sr addition up to 8 % doping, followed by an increase. Random Free-Energy Barrier Model (RBM) was employed to analyze complex AC conductivity. The three-dimensional Godet's Variable Range Hopping (3D G-VRH) model was also applied to elucidate the electrical transport properties.