In the last few years, multiferroic materials are emerging as a material of choice to realize memory based devices, sensor based devices and optoelectronic based devices. Among the several multiferroic materials, bismuth ferrite (BFO) appears to be a potential candidate for photovoltaic devices due to its relatively lower optical bandgap (2.08 - 2.7eV) and large remnant polarization (90 μC/cm~2). It is also suitable for memory devices due to the co-existence of different ferroic orders and a large remnant polarization. However, the practical application of this material is still hindered due to the inherent limitations which include large leakage current and pure phase formation of BFO compound. Keeping this view in mind, we have successfully synthesized the pure phase of BFO nanoceramics by adopting low temperature sol - gel synthesis route. Furthermore efforts were devoted to study the effect of annealing temperature and its duration on the structural, morphological and optical properties of these ceramics. The as-prepared samples were calcined at 400°C and subsequently annealed at various temperatures (500°C, 550°C and 600°C) for different durations (2h, 4h and 6h). Interestingly, the sample annealed at 550°C for 2h yielded pure phase of BFO ceramics and the average crystallite size of these ceramics was found to be increasing with both increase in annealing temperature and duration. The Fourier transform infrared spectra (FTIR) recorded for all these samples exhibited strong absorption bands in the range of 400 - 600 cm~(-1), which corroborated the perovskite structure of BFO nanoceramics. The microstructural analyses have revealed the existence of granular shaped grains with negligible porosity in all the samples studied. Furthermore, the samples annealed at higher temperatures for longer duration showed the agglomeration of the grains in the scanning electron micrographs. The optical bandgap was determined for all the samples prepared under various annealing conditions by Tauc's method. Interestingly, it was found that the value of bandgap of these ceramics could be tuned as a function of annealing temperature and duration. For instance, the value of the optical bandgap obtained for the pure sample annealed at 550°C for 2h was found to be 2.08 eV. Therefore, in this present investigation, the tailoring of physical properties of BFO nanoceramics by aforementioned thermal treatment could be beneficial for designing memory as well as photovoltaic devices.
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