Band gap tuning in nanocrystalline SrTi0.9Fe0.1O2.968 perovskite type for photocatalytic and photovoltaic applications

Abstract

In the present work and for the first time, tuning of the band gap width of the SrTiO3 (STO) perovskite to a value suitable for photocatalytic (PC) and photovoltaic (PV) applications is accomplished by the incorporation of Fe cation. Nanocrystalline SrTi0.9Fe0.1O2.968 (STFO) was prepared by a modified solid state reaction process including successive sequences of milling and calcinations at high temperature. The X-ray diffraction (XRD) pattern revealed the formation of a single cubic perovskite phase of STFO with average crystallite size equaling ⁓30 nm. The local lattice strain on (h00) and (hh0) planes was found to decrease by Fe doping. The absorption spectrum deduced from diffused reflectance showed high intense broad structure extending over the range ⁓0.5 – ⁓6 eV, whereas pure STO gave strong absorption only at the UV region (λ < 400 nm). The deduced band gap width of the STFO sample was 1.43 eV; an ideal value for PC and PV applications. Deconvolution of the broad absorption band revealed the presence of four absorption structures attributed to Fe defect centers. The narrowing of the band gap was also confirmed through the photoluminescence study where many emission lines covering the violet-blue region were detected. The type of the Fe species and the relative abundance of Fe3+ and Fe4+ were determined by Mössbauer spectroscopy. The presence of oxygen vacancies and Fe-OV complexes were also supposed as lattice defects located above the O2p and below the Ti-3dt2g states. The novel electronic structure researched in this study offers a new avenue in the field of band gap engineering for future application in the field of photocatalytic materials.