Role of La substitution on structural, optical, and multiferroic properties of BiFeO3 nanoparticles

The present work reports the influence of Lanthanum (La) substitution on the structural, optical, electrical, and magnetic properties of bismuth ferrite (BiFeO3) nanoparticles (NPs). The compositions of Bi1-xLaxFeO3 (0% < x < 20%) NPs, with 5% Bi-excess, were synthesized through sol-gel conventional route. The XRD results suggest the formation of rhombohedral perovskite structure (R3c space group) along with a minor secondary phase. The crystallite size calculated from XRD and FESEM was observed to decrease from 60.0 to 40.0 nm with an increase in La content. The bandgap calculated using UV-Vis spectroscopy was found to decrease with La doping, and PL spectroscopy infers formation of defects in La-BFO NPs. The P-E loop studies reveal that La-doped BFO exhibits ferroelectric behavior at room temperature. The various parameters such as spontaneous polarization, dielectric constant, and distribution parameter of relaxation time measured from the electrical investigation were found to increase up to 5% La doping BFO then start decreasing with further increase in the La content in BFO. The impedance spectra of La-BFO was fitted using the theory of Cole-Cole with R(C(R(QR)))(CR) model. It is observed that La-concentration above 5% generates excess space charge which might cross the threshold to start conduction resulting in degrading of multiferroic properties. The DC magnetization study revealed the ferromagnetic behavior of the samples at room temperature. It is observed that La substitution affects the shape of the magnetization hysteresis curve beyond 5% La-concentration, and transforming it to a neck-like formation providing evidence for the spin-canting effect in the samples. These results make La-doped BiFeO3 NPs a propitious candidate for the multiferroic applications like high-density data storage devices and supercapacitors.