The Effect of Annealing Temperature on the Bandgap of Bi3.25La0.75FeTi2O12 Powders.

In recent years, there has been increasing interest in the bandgap engineering of ferroelectric oxides to improve absorbance of the solar spectrum, which is governed by their band gap. To enhance the photovoltaic efficiency by tuning the optical bandgap of complex oxides, an attempt was recently made to reduce the optical band gap of iron doping of lanthanum-modified Bi4TiO12-based oxides (Fe-BLT) using oxygen vacancy doping. To study the tunability of the optical band gap from the generation of oxygen vacancies, the thermal treatment time and temperature were controlled during heat treatment under a vacuum environment. The structural, optical properties of the synthesized podwers were examined by X-ray diffraction, scanning electron microscopy, and ultraviolet-visible spectroscopy. Typically, an oxygen vacancy in a complex oxide can alter their structure very easily. On the other hand, the ultraviolet-visible absorption spectra of iron-doped bismuth titanate ceramics under optimal conditions (12 h, 800 °C) showed a decrease in optical bandgap. from 2.02 eV to 1.8 eV without a corresponding change in their crystallographic structure. This study suggests that optimal control of the thermal treatment time and temperature critically effects the optical band gap of complex oxides.