Band gap energy of perovskite structured ABO3 compounds

Band gap energy for nonstoichiometric BaTiO3 and perovskite structured ABO3 compounds have been investigated in regard to the relationship among band gap energy, defect chemistry, and crystal structure. The band gap energy was determined by UV-Visible spectrophotometer for powder samples, which are synthesized by citrate process and ultrasonic mixing to avoid the impurity effects. The band gap energy of nonstoichiometric BaTiO3 varied systematically in the solubility region around stoichiometric BaTiO3, indicating that the partial Schottky defects affect to the band gap energy. The band gap energy for ABO3 compound had systematic trends with each parameter such as ionic size, lattice size, B-O bonding distance, tolerance factor, etc. Lattice volume and tolerance factor showed a single trend with band gap energy, but unlike simple binary compounds, the band gap energy for ABO3 compounds had a complex trend with the bonding distance. In addition to the simple ABO3 compounds, in the solid solution system for two different end members of ABO3 compounds, the lattice tilt effect on band gap energy will be discussed. This study provides an insight in understanding the origin of band gap energy and engineering the band gap energy.