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Raman scattering study of polycrystalline BiFeO3 obtained by mechanochemical synthesis
|Zorica Marinkovic-Stanojevic 2, Nebojsa Romcevic 1, Branka Hadzic 1, Biljana Stojanovic 2
1. Institute of Physics (IF), Pregrevica 118, Belgrade 11080, Serbia
A powder mixture of Bi2O3 and Fe2O3 was mechanically tretaed in a planetary ball mill in air atmosphere for 120, 240, 360 and 720 minutes. Samples were denoted according to the time of milling as BFO120, BFO240, BFO360 and BFO720. Mechanochemical reaction leads to the gradual formation of polycrystalline BiFeO3 (BFO) at room temperature. After 240 min of synthesis, all of the reflection peaks can be indexed as BFO rhomohedral R3c crystallographic structure. Highly dense and single-phase BFO ceramics were prepared by conventional solid-state reaction at the temperature of 810oC for 1h followed immediately by quenching process.
Raman scattering study of polycrystalline BFO ceramics were carried out at room temperature. Most of the 13 Raman modes predicted by group theory ( ГRaman, R3c = 4A1 + 9E) for R3c structure of BFO are observed in the present work. There are nine normal modes, including A1-1, A1-2, and A1-3 modes with strong scattering intensity, and six E modes with medium scattering intensity. The results of Raman spectra matches well with the recently reported single crystal and epitaxialy grown thin film of BFO. The observed three A1 modes should be governed by the Bi-O covalent bonds, which are the origin of the ferroelectric distortion. The Raman spectra suggest that the ferroelectric distortion of BFO360 sample is more stable than that of BFO120, BFO240 and BFO720 due to the weakening of the scattering intensities of the A1 modes in these samples.
The slight difference in some of the peak positions observed in investigated samples can be attributed to the sample preparation details. It is known that mechanochemical synthesis influences the oxygen stoichiometry. This is expected to show changes in oxygen bonding and disorder that is reflected in the vibrational frequencies of mode involving oxygen.
Presentation: Poster at E-MRS Fall Meeting 2008, Symposium A, by Nebojsa Romcevic
See On-line Journal of E-MRS Fall Meeting 2008
Submitted: 2008-05-12 11:58 Revised: 2008-06-26 17:28