Yao Lu; Xiangxiao Meng; Zhipeng Pei; Kai Leng; Weiren Xia; Xinhua Zhu
Abstract
Double perovskite Ba2FeNbO6 (BFN) powders were synthesized by molten salt method. Their optical properties were characterized by UV-Vis absorption spectra, and the band gaps (Eg) were determined to be 2.12 - 2.25 eV. The Eg values were tuned by adjusting the processing parameters ...
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Double perovskite Ba2FeNbO6 (BFN) powders were synthesized by molten salt method. Their optical properties were characterized by UV-Vis absorption spectra, and the band gaps (Eg) were determined to be 2.12 - 2.25 eV. The Eg values were tuned by adjusting the processing parameters of molten-salt route (e.g., annealing temperature, holding time as well as the molten salt ratios). The varied Eg values are ascribed to the different content ratios of Fe 3+ to Fe 2+ ions and the oxygen vacancies in the BFN powders. Oxygen vacancies in the BFN powders result in the distortions of FeO6 octahedrons, leading to different Fe-O bond lengths. Thus, the overlapping between the O-2p < /em> and Fe-3d orbitals is changed, making the Eg values changed. A small absorption shoulder with absorption edge at 650 nm (Eg ~ 1.91 eV) observed in the BFN powders, was ascribed to the d-d electronic transition from the Fe 3d-b2g to Fe 3d-b1g orbitals, which were formed by further splitting of Fe 3d orbitals in the distorted octahedral field. The present work offers an effective approach to tuning the Eg of BFN powders, which find promising applications in the fields of photovoltaic and photocatalytic devices.
Peng Song; Zhipeng Pei; Heng Wu; Yao Lu; Weiren Xia; Xinhua Zhu
Abstract
Double-perovskite structured multiferroic Bi2FeMnO6 (BFMO) ceramics synthesized via solid-state reaction route at 880 o C for 3 h, crystallized in a distorted rhombohedral structure with R3c space group. Their lattice parameters in the hexagonal system were determined to be a = 5.571 Å and c = ...
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Double-perovskite structured multiferroic Bi2FeMnO6 (BFMO) ceramics synthesized via solid-state reaction route at 880 o C for 3 h, crystallized in a distorted rhombohedral structure with R3c space group. Their lattice parameters in the hexagonal system were determined to be a = 5.571 Å and c = 13.191 Å. SEM images show that the BFMO ceramic grains exhibit spherical morphology with an average size of 6.70 mm. Their atomic ratio of Bi:Fe:Mn was determined to be 2.07:1.02:1.00, close to the nominal value of 2:1:1. Raman spectra have verified the vibrational frequencies in the BFMO ceramics, and only 11 Raman active modes are observed. The less observed Raman modes in the BFMO ceramics compared with the theoretical group analyses, can be ascribed to the small correlation field splitting of the ceramic samples due to their polycrystalline nature. BFMO ceramics exhibit almost frequency-independent dielectric behavior in a frequency range of 500 - 10 6 Hz at room temperature. Their dielectric constant and dielectric loss were measured to be 700 and 0.03 at 10 6 Hz, respectively. The piezoelectric moduli d33 of the poled BFMO ceramics was measured to be 56 pC/N, which is two times larger than that reported for BiFeO3 thin film (d33 ≅ 25 pC/N). Copyright © VBRI Press.
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