Structural, Optical, and Magnetic Properties of Brownmillerite KBiFe<sub>2</sub>O<sub>5</sub> and KBiFe<sub>1.95</sub>Ti<sub>0.05</sub>O<sub>5+</sub> via Reactive Templated Method
Peshal Karki, Rajasekhar Bhimireddi, Lokeswararao Dhavala, A.V. Anupama, Apparao M. Rao, K. Kanmani Raja, Anees A. Ansari
Abstract
High Resolution Image Download MS PowerPoint Slide Brownmillerite KBiFe 2 O 5 (KBFO) and KbiFe 1.95 Ti 0.05 O 5+ (KBFTO) ceramics were synthesized using the prereacted nanopowders of KFeO 2 (KFO) and BiFeO 3 (BFO), and KFO and BiFe 0.95 Ti 0.05 O 3+ (BFTO), respectively, via the reactive templated method. The powder X-ray diffraction patterns confirmed the monoclinic phase of the KBFO and KBFTO samples. The incorporation of Ti 4+ at Fe 3+ site prevented the formation of a secondary phase (Bi 2 Fe 4 O 9 ) in the KBFTO sample. Our experimentally determined lattice parameters for the orthorhombic P 2/ c KBFO and KBFTO are consistent with our density functional theory (DFT) computed lattice parameters (within a 5% error). Scanning electron microscopy images revealed an average grain size of ∼1.38 and 0.85 μm for KBFO and KBFTO, respectively. The calculated optical band gaps of the KBFO and KBFTO using the Kubelka–Munk function from their UV data were found to be 1.69 and 1.71 eV, respectively. The measured surface area of KBFTO (1.339 m 2 g –1 ) obtained from BET analysis was double that of KBFO (0.698 m 2 g –1 ). KBFTO’s room-temperature magnetization was 0.986 emu g –1, which was twice that of the KBFO, while its room-temperature conductivity measured using impedance spectroscopy was 5.69 × 10 –3 S m –1 which was 10 times that of KBFO. Notably, our DFT calculations showed that the small Ti dopant concentration enhanced the partial density of states (PDOS) above the Fermi level. It shifted the Fermi level toward higher energy, and the oxygen PDOS for KBFTO was significantly enhanced relative to KBFO, which ultimately helped improve the conductivity.