Tuning the band gaps of ferroelectric Aurivillius compounds by transition metal substitution

A wide bandgap is one of the major obstacles that hamper the photoelectric application of ferroelectrics. This work reported the tunable band gaps of ferroelectric Aurivillius Bi3.15Nd0.52Ti3O2 (BNdT) by B-site X (X = Ni, Co, Cr Mn, or Fe) substitution. The analysis of the UV-vis absorption spectra showed a decrease in the band gap induced by substitution and the valence band XPS (VBXPS) spectra indicated that the substitution of X ions elevates the valence band maximum (VBM). The octahedral distortion was estimated qualitatively by Raman analysis and quantitatively through the structural refinements. It is found that the change of the energy band structure and the band gap tuning are proportional to the octahedral distortion induced by B-site substitution. To our knowledge it's the first time to relate the octahedral distortion to the band gap tuning quantitatively for ferroelectric Aurivillius compounds, and the present work will shed light on the mechanism of band gap tuning of ferroelectric oxides materials and provide an available way on manipulating oxide optoelectronics.