Influence of structural and morphological variables on the optical and electrical response of Na-doped BFOs

Abstract

In this study, the influence of p-type doping with Na atoms on the optical bandgap and electrical conductivity of a series of bismuth ferrites (BiFeO₃) synthesized by a low-cost solid-state method was evaluated. To identify the properties that influenced the bandgap and electrical response of the samples, the phase of interest was identified and quantified by X-ray diffraction (XRD), the morphological characteristics were determined by scanning electron microscopy (SEM). Structural properties were elucidated by spectroscopic techniques and finally the optical response (indirect bandgap) was measured by ultraviolet–visible spectroscopy (UV–Vis) and electrical response (conductivity) by solid-state electrochemical impedance spectroscopy (SS-IES). The results of this work demonstrated that the optical and electrical response of the series of Na-doped BiFeO₃ samples is dependent on at least eight structural and morphological variables (sodium ratio, purity, unit cell volume, oxygen vacancy concentration, crystalline domain size, structural microdeformations, particle size and Warburg-type resistive phenomena). Among the most relevant results, the influence of purity, intrinsic and physical defects was identified, observing a decrease of the electrical resistance and energy gap with the presence of Na.