Effect of calcination temperatures on the band gap of Bismuth Ferrite (BiFeO3) – A First Principle Study

Abstract

In the present thesis, effect of calcination temperatures on the band gap of BiFeO3 is reported. DFT calculations were performed using GGA+U methodology in the TB-LMTO-ASA code version 47. The ground state electronic properties of BiFeO3 were calculated using the combination of U = 6eV and J =1eV for the Hubbard parameters while keeping the spins of two Fe atoms (Fe1 and Fe2) in the opposite spin directions in the 10 atoms unit cell of BiFeO3, which confirmed the value of band gaps and the nature of band gaps obtained experimentally at two calcination temperatures i.e. 500°C and 600°C. After, the SCF calculations were performed using the rietveld refinement data for the ground state (R3c) BiFeO3 calcined at 500°C and 600°C, equal electronic band structure diagrams were obtained in the two spin directions. Also, the equal partial density of states plots were obtained for oxygen as well as bismuth in contrast with different partial density of states plots for Fe1 and Fe2 atoms in the two spin directions thereby authenticating the anti- ferromagnetism in case of bulk BiFeO3 at both the calcination temperatures of 500°C and 600°C, respectively. Also, the direct band gap values of 2.25eV and 2.16eV were obtained from the TDOS (including both spin1 and 2 directions) closely approximates both the experimental direct band gap values of 2.16eV and 2.25eV at 500°C and 600°C, respectively. Lastly the charge density plot was calculated in a plane to study the nature of chemical bonding among the constituent atoms of BiFeO3 through which it was concluded that the chemical bonding between the Fe and O atoms is not completely ionic with partially directional covalent bonding thrown in it thereby indicating the non-Centro symmetric setup leading to Ferro electricity observed in case of bulk BiFeO3