Crystal field modification via rare earth ions (Dy, Nd) incorporation on BiFeO3 fine nanoparticles

Rare earth (Dy, Nd)-doped and co-doped multiferroic bismuth ferrites nanoparticles (NPs) with formulas Bi1 - xDyxFeO3 (x = 0, 0.02 and 0.04), Bi1-yNdyFeO3 (y = 0.02 and 0.04) and Bi1- x-yDyxNdyFeO3 (x = 0.02 and y = 0.02) were synthesized by a controlled hydrothermal process. X-ray diffraction (XRD) confirmed the presence of the typical rhombohedral distorted perovskite structure of BiFeO3 (BFO) for all synthesized nanopowders. Whereas a slight impurity phase started to appear in both 4% Dy- and 4% Nd-doped BFO samples. The crystallite sizes as determined by Scherrer equation were found to increase slightly with doping. In close agreement, images seen by TEM confirmed the size of nanoparticles. EDX analysis confirmed the presence of elements in such sample. Optical study revealed a clear crystal field and band structure modification. Direct optical bandgap determined through Tauc plot deduced from reflectance measurement showed a remarkable decrease in value. The real and imaginary parts of dielectric constant (epsilon', epsilon") show a maximum increase on co-doped BFO concomitant with remarkable increase in dielectric loss (tan delta) which indicates substantial enlarge in leakage current density. Further, the pure BFO shows a well-defined dielectric loss peak, which shifts toward higher frequency for doped NPs. Vacancies proliferation is one of the main sources of movable space charges in BFO and, through, for leakage current.