Stability and physical properties of the K, Na and Nb doped BiFeO3 lead-free system synthesized by the solid state route

Abstract

A study of the structural, dielectric, and optical properties of the lead-free ceramic compound (1-x)BiFeO3–(x)(K0.5Na0.5)NbO3 [(1-x)BFO-(x)KNN] prepared by the solid-state reaction method is presented. The structural analysis was carried out by performing Rietveld refinement on the X-ray diffraction data showing a distorted rhombohedral structure of the R3c space group for all samples. The presence of all active Raman modes confirms this result. The effect of K, Na, and Nb incorporation in the BFO structure is clearly seen in the scanning electron microscopy micrographs of the samples, and energy dispersive x-ray spectroscopy (EDS) confirms the existence of all elements. Piezoelectric force microscopy analysis reveals a well-defined domain structure for the higher concentrations of KNN as well as ferroelectric switching behavior. The room temperature dielectric response increases with KNN doping. A small hump in the dielectric permittivity vs. temperature plots is observed near 350 °C and is ascribed to a para-antiferromagnetic phase transition at the Nèel temperature. An optical absorption study revealed that tuning of the bandgap energy is possible through controlled doping, as shown in the present case, where the bandgap varies from 2.16 eV for x = 0.0 to 1.93 eV for x = 0.08. The results of this investigation demonstrate that K, Na, and Nb doping is an effective way to enhance the dielectric and optical properties of BFO.