Investigating the influence of Cu and Ti substitution on the structural, optical, and dielectric properties of BiFeO3

Abstract

The environmentally friendly BiFe_1−x(Ti_1/2Cu_1/2)_xO₃ system with various substitution rates, including x = 0 (BFO), x = 0.02 (BFTCO₂) and x = 0.04 (BFTCO₄), has been synthesized using the solid-state reaction technique. All compositions exhibited a distorted rhombohedral structure with R3c space, as observed from the results of XRD and Raman spectroscopy. A significant impurity phase (Bi₂₅FeO₄₀) appears in pure and doped BFO, with a percentage ranging between 6 and 9%. This impurity was also detected using Mössbauer spectroscopy. UV-vis spectroscopy revealed a decrease in optical band energy with the substitution, suggesting the potential applications of doped BFO within the visible range of the spectrum, making it suitable for photocatalytic and solar cell applications. The smallest bandgap was observed for BFTCO₂ with E_g = 1.93 eV. The origin of this reduction is discussed from a scientific point of view. Furthermore, Cu²⁺ and Ti⁴⁺ co-doped BFO display an improvement in dielectric properties due to the reduction in the value of tan δ. Dielectric measurements revealed an anomaly below T_N with diffusive and dispersive behavior, suggesting a relaxor-like behavior for all compositions. The relaxor character was quantified by using the Vogel–Fulcher relationship which yielded activation energy of 0.359–0.614 eV. In our system, the relaxor behavior showed an enhancement with the heterogeneity created by the substitution rate, reaching its maximum for BFTCO₄, characterized by the empirical parameters which are: ΔT_relax = 96 K and γ = 1.96. Finally, co-doped BFO ceramics not only present promising materials for optical applications due to the narrow bandgap, but their relaxor behavior can also be tailored for promising applications in high-energy storage devices.