Symmetry-dependent bandgap evolution with Zr-substitution in BaTiO3

Abstract

Zirconium-substituted barium titanate (BaTi<inf>1-x</inf>Zr<inf>x</inf>O<inf>3</inf>) has emerged as a model system for study of relaxor behavior in ferroelectric perovskites. Substitution of Zr drive relaxor behavior as well as structural phase transition tetragonal to cubic symmetry around x = 0.15. While this material has been thoroughly examined for relaxor behavior and other potential applications, the study of optical bandgap around phase transition lacking. The present work investigates the effect of Zr content on the optical bandgap across this phase boundary. The structural evolution with Zr concentration was systematically characterized using X-ray Diffraction confirming the tetragonal-to-cubic phase transition. Optical bandgaps were extracted from diffuse reflectance spectroscopy using Tauc analysis. Our results reveal a distinct non-linear trend in bandgap variation with Zr concentration, with a notably higher rate of change in the tetragonal phase compared to the cubic phase. This behavior is attributed to changes in type of orbital overlap and interatomic distances driven by both compositional modification and symmetry change. These findings emphasize the strong correlation between crystal structure and electronic properties in perovskite oxides, offering valuable guidance in bandgap engineering in optoelectronic applications. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2026.