Tunable bandgap in BiFeO3 nanoparticles: The role of microstrain and oxygen defects

Abstract

We demonstrate a tunable bandgap from 2.32 eV to 2.09 eV in phase-pure BiFeO3 by controlling the particle size from 65 nm to 5 nm. Defect states due to oxygen and microstrain show a strong dependence on BiFeO3 particle size and have a significant effect on the shape of absorbance curves. Oxygen-defect induced microstrain and undercoordinated oxygen on the surface of BiFeO3 nanoparticles are demonstrated via HRTEM and XPS studies. Microstrain in the lattice leads to the reduction in rhombohedral distortion of BiFeO3 for particle sizes below 30 nm. The decrease in band gap with decreasing particle size is attributed to the competing effects of microstrain, oxygen defects, and Coulombic interactions.

Dy doped BiFeO 3 : A bulk ceramic with improved multiferroic properties compared to nano counterparts

“…This implies that with particle size reduction, the amount of lattice mismatch and dislocations increased. Such results are consistent with findings reported in [35]- [36].…”

Substitution-driven structural, optical and magnetic transformation of Mn, Zn doped BiFeO

“…The band gap energy has been found as 1.47 (7 0.04) and 1.65 ( 7 0.03) eV for 5% and 10% Zn-doped, 1.54 ( 7 0.04) and 1.73( 7 0.01) eV for 5% and 10% Mndoped and 1.5 eV for Mn, Zn co-doped samples respectively. Several parameters including microstructure [26], chemical structure [27] and defects [28] may affect band gap value. Metal ion doping is an effective way to develop visible-lightdriven photocatalysts.…”

Ferroelectric and magnetic properties of magnetoelectric (Na0.5Bi0.5)TiO3–BiFeO3 synthesized by acetic acid assisted sol–gel method

“…The spectral changes observed for BFO is similar to some recent reports. 11,35 The absorption edge at 500 nm corresponds to the charge transfer from valence band O 2p states to conduction band Fe-3d states. The broad band observed at 650 nm is due to the d-d transition of Fe 3+ states.…”