Effects of Cu and Zr Co-substitution on the structural, dielectric, and optical properties of BiFeO₃ ceramic

Multiferroic materials, particularly BiFeO₃ (BFO) and its derivatives, have gained significant interest due to their potential applications in energy storage and photocatalysis. In this study, we investigate the effect of the low concentration (2%) of co-substitution with (Zr, Cu) on the structural, vibrational, optical, dielectric and ferroelectric properties of BFO. Both pristine BFO and BiFe_0.98(Zr_1/2Cu_1/2)_0.02O₃ (BFCZ02) were synthesized through the solid-state reaction method. X-ray diffraction analysis revealed the good crystalline nature of both compositions, with the formation of impurities such as Bi₂₅FeO₃₉. Rietveld refinement and Raman analysis confirmed a consistent rhombohedral structure with the R3c space group for all samples. The average crystallite size decreased from 61.08 nm (BFO) to 39.08 nm (BFCZ02), indicating doping-induced grain refinement. Dielectric permittivity was studied over a wide temperature range (300-700 K) at various frequencies. An anomaly corresponding to the Néel temperature (T _N) was observed at 623 K for pure BFO, which decreased significantly to 604 K upon the co-substitution. A possible explanation for this shift was proposed. UV-visible spectroscopy at room temperature showed absorption peaks between 400 and 440 nm for both ceramics. The optical bandgap energy was estimated to be 2.34 eV for BFO and 2.21 eV for BFCZ02, suggesting the importance of the co-substitution of BFO in visible-light photocatalysis and photovoltaic applications. Possible reasons for the reduction in bandgap were proposed and discussed. The P-E loop study of the samples shows the modified ferroelectric behavior with Zr and Cu co-substitution. The results demonstrate that co-substitution with Zr and Cu enhances the optical response, improves dielectric performance, positioning BFCZ-02 as a promising candidate for multifunctional applications, including photovoltaics, photocatalysis, energy harvesting, and adaptive dielectric devices.