First-principles study of BiFeO₃and BaTiO₃in tetragonal structure

Abstract

Structural, electronic, magnetic and mechanical properties of the perovskites BiFeO3 (BFO) and BaTiO3 (BTO) are investigated using density functional theory (DFT). Structural and mechanical parameters are calculated using generalized gradient approximation (GGA) and the results consistent with the available literature. The stable magnetic phases are achieved by optimizing total energies versus volumes of the cells in different magnetic configurations such as nonmagnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM). BTO is found to be NM while BFO favors G-type AFM (G-AFM) phase. The electronic properties are investigated using GGA, GGA with Hubbard potential (GGA[Formula: see text]+[Formula: see text]U) and modified Becke–Johnson (GGA-mBJ) exchange–correlation functionals. BFO is found to be a direct bandgap semiconductor having gap energy value 3.0 eV whereas BTO is an indirect semiconductor with bandgap energy 2.9 eV. Spin–orbit coupling effect is dominant in BFO due to the larger size of A-site cation. The electrical polarization shows that both the compounds are ferroelectric materials with significant spontaneous polarization of 144.1 [Formula: see text]C/cm2 and 27.9 [Formula: see text]C/cm2 for BFO and BTO respectively.

Enhancing ferroelectric photovoltaic effect of BaTiO3 by the lateral interface

“…The bandgap of BaTiO 3 is 2.46 eV by our calculation, which is in good agreement with the previous theoretical results (2.4 eV) 30 , but is lower than the experimental data (3.4 eV) 36 . And the bandgaps of BaO/BaTiO 3 is 1.49 eV, which is lower than that of BaTiO 3 , indicating that the formation of interface obvious decrease the bandgap of BaTiO 3 .…”

“…Here, the effective Hubbard parameter U eff = U (Hubbard parameter) − J (exchange interaction) 29 was adopted. The values of U eff were set to 4 eV for the Ti 3 d states 30 . The Berry‐phase calculations 31,32 (the so‐called “modern” theory of polarization) is performed to calculate the polarization.…”

Potential High-Temperature Piezoelectric Ceramics with Remarkable Performances Enhanced by the Second-Order Jahn–Teller Effect

“…After losing three and two electrons to form Bi 3+ and Pb 2+ , there were two electrons existing in the s orbital for Bi and Pb. As seen, the energy of the electrons ranging from −8 to 2 eV in the s orbital was observed to be very homogeneous, which was confirmed by the mild and almost close to the line, for which the same wider peaks occurred in other works . Nevertheless, the energies of the electrons in the p and d orbital displayed much more binding, which was verified by several sharp peaks.…”

Cocatalyst Engineering in Piezocatalysis: A Promising Strategy for Boosting Hydrogen Evolution

“…A is a constant and n is 2 considering that BiFeO 3 is a direct band gap semiconductor. 54 According to the curve plots for (αhv) 2 versus hv in the inset of Figure 5a, the optical band gap of BiFeO 3 is determined to be 2.25 eV, which is not altered after the introduction of Pd. As revealed by the Mott−Schottky plots (Figure 5b), BiFeO 3 exhibits n-type semiconductor characteristics given that the curve of 1/C 2 versus potential is upward sloping, and the flat band potential of which is determined to be −0.85 V versus the Ag/AgCl electrode (vs Ag/AgCl), equivalent to −0.65 V versus the normal hydrogen electrode (vs NHE).…”

“…According to the UV–vis diffuse reflectance spectra (Figure a), BiFeO 3 is a narrow-band-gap semiconductor and the band gap of which is determined by using the equation where α, hv , and E g are the absorption coefficient, light energy, and optical band gap, respectively. A is a constant and n is 2 considering that BiFeO 3 is a direct band gap semiconductor . According to the curve plots for (α hv ) 2 versus hv in the inset of Figure a, the optical band gap of BiFeO 3 is determined to be 2.25 eV, which is not altered after the introduction of Pd.…”