Effect of simultaneous chemical substitution of A and B sites on the electronic structure of BiFeO_3 films grown on BaTiO_/SiO_2/Si substrate

摘要

Electrical properties and electronic structure of Bij_(1-x)Ca_xFe_(1-y)Mn_yO_(3-δ) grown by pulsed-laser deposition on BaTiO_3/SiO_2/Si substrate were investigated. Results showed that Ca has drastic effect on symmetry of crystal and electrical poperties of BiFeO_3. On the other hand, Mn revealed to have more radical effect on optical properties and energy gap of the compound. XPS results represented that although Ca tend to decrease Fe valence state, Mn tends to stabilize it at 3+ (at least in this concentrations). UV-visible study yielded bandgap of 2.51-2.81 eV (at 300 K) for different concentrations of Ca and Mn. UV-visible spectra also revealed sub-bandgap defect transitions at 2.2 and 2.4 eV. Slave-particle approach has also been applied to elucidate nature of the metal-insulator transition.