Influence of divalent Ni and trivalent Cr ions on the properties of ytterbium modified bismuth ferrite

Different concentrations of Ni²⁺ and Cr³⁺ ions are individually doped in the Fe site of Bi_0.95Yb_0.05FeO₃ and its effect on structural, band gap, magnetic and electrical properties of bismuth ferrite is analyzed. Samples are synthesized using citrate based sol-gel method. XRD pattern of all the samples confirmed the formation of BFO with rhombohedral crystal structure. Reflectance spectra of the samples show band corresponding to charge transfer and d-d transitions in Fe. The direct band gap of the samples is calculated using Kulbeka-Munk theory. When compared to Yb modified BiFeO₃, an enhancement of magnetization is observed in the Ni co-doped samples and variation with increase in Cr concentration is seen. All the Ni co-doped samples display high leakage behavior, whereas 1, 3 Cr co-doped samples show low leakage and an increase is observed for 5% Cr concentration. The conduction mechanism responsible for the leakage behavior in the Ni co-doped and Cr co-doped samples is found to be different. Ferroelectric measurements show ferroelectric behavior in all the samples. In Ni co-doped samples, the conducting nature has an influence on observed ferroelectric behavior.