Structural, optical, electrical, and dielectric relaxation properties of rare earth containing sodium bismuth titanate [formula omitted] perovskite: Effect of ionic radius

Abstract

The main focus of this work is to study the effect of the ionic radius of different rare earth dopant cations RE3+ (RE = La, Sm, Dy, and Ho) on structural and various physical properties of sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) based perovskite nanomaterials. The X-ray diffraction data indicate the successful formation of the rhombohedral phase (space group R3c) of NBT nano perovskite incorporated with various rare earth ions in Bi-site. The lattice parameters were found to increase linearly with the ionic radius of the dopant cation. The ionic radii and atomic mass of rare earth dopants appear to be essential factors in the grain growth of the prepared compositions. The grain growth results in better crystallinity of the sample by reducing the microstrain with the increase of dopant ionic radius. Field emission scanning electron microscopy and energy-dispersive X-ray spectra confirm the prepared compositions' phase purity and stoichiometry. The UV–Vis spectra reveal that La-doped NBT composition exhibits the lowest optical band gap, which unfolds the application of NBT-based perovskite as photoactive material. The ac conductivity and complex impedance spectra unveil that the composition with the largest ionic radius, i.e., La-doped NBT compound, exhibits the highest dc and bulk conductivity with the lowest activation energy. The frequency-dependent dielectric data follows Havriliak–Negami (HN) formalism and non-Debye type relaxation phenomena. Results also indicate that La-doped NBT composition exhibits the highest dielectric strength value. Thus, this study first elaborates that the increasing ionic radius of the rare earth dopant cation in the Bi-site of NBT perovskite improves its microstructural, optical, and electrical properties.