Naslov
The mechanism of BiFeO3 hydrothermal synthesis

Autori
Gajović, Andreja ; Šturm, Sašo ; Jančar, Boštjan ; Čeh, Miran

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
EUCMOS 2008 XXXIX European Congress on Molecular Spectroscopy Book of Abstracts / Svetozar Musić, Mira Ristić, Stjepko Krehula - Zagreb : Institut Ruđer Bošković, 2008, 161-161

Skup
EUCMOS 2008 XXXIX European Congress on Molecular Spectroscopy

Mjesto i datum
Opatija, Hrvatska, 31.08.2008. - 05.09.2008

Vrsta sudjelovanja
Poster

Vrsta recenzije
Domaća recenzija

Ključne riječi
BiFeO3; multiferroic; Raman spectroscopy; HRTEM

Sažetak
The perovskite bismuth ferrite BiFeO3 is a multiferroic material – ferroelectric (TC = 1103 K) and antiferromagnetic (TN = 643 K) – exhibiting weak magnetism at room temperature. Since the spins in this material take the form of a long-wavelength (62 nm) the spiral linear magnetoelectric effect averages to zero. One of the ways to recover the linear effect is by thin-film epitaxial constraints [1] ; so we expected the same effects in nanostructured BiFeO3. The phases appearing in the hydrothermal reaction in the Fe– Bi– O system were investigated, with the aim to study the conditions for the synthesis of nanostructural bismuth ferrite. For the hydrothermal reactions a series of precipitations, with various molar ratios of iron and bismuth ions, were carried out. The solution of iron and bismuth salt was co-precipitated with a strong hydroxide to high pH values. The hydrothermal treatments were performed for 6 h at 200°C in a stainless-steel Teflon-lined autoclave. The phase composition of the samples was studied by micro-Raman spectroscopy (RS) and was compared with X-ray powder diffraction (XRD) results. To avoid laser-induced thermal effects on the samples during the recording of the Raman spectra the laser power was carefully optimized. The morphologies and nanostructures of the different phases were determined using high-resolution transmission electron microscopy (HRTEM) and/or scanning electron microscopy (SEM). The chemical composition at the nanoscale was determined with energy-dispersive X-ray spectroscopy (EDXS). BiFeO3 was detected only in the samples with a higher content of Bi3+ ions, while in the case of the lower content of Bi3+ ions only the iron oxide and/or the iron-hydroxide phases with different Bi-doping were observed. Raman spectroscopy was used to clarify the possible existence of metastable maghemite or magnetite [2] in the samples with 3.5 and 5 mol% of bismuth, since it is difficult or impossible to distinguish between these two phases just from the XRD results. In the samples with 7.5 and 10 mol % of Bi3+ ions in the reactions, the hematite phase dominated. We observed that the bismuth ferrite did not form at these low Bi3+ concentrations and was detected only for contents above 30 mol%. However, at 20% of Bi3+ content a poorly crystalline, nanosized phase appeared during the sintering. This phase implies a formation step between the doped iron oxide/hydroxide phases and the BiFeO3. RS, XRD and HRTEM results have to be combined for a proper and complete meaningful evaluation. In spite of the difficulties in synthesizing pure BiFeO3 [3], this was achieved in a hydrothermal reaction with 50 mol% Bi3+. The mechanism of the BiFeO3 synthesis will be discussed in terms of the observed stable and metastable phases. [1] W. Eerenstein, N. D. Mathur and J. F. Scott, Nature 442 (2006), p.759 and the references therein. [2] D. L. A. de Faria, S. Venancio Silva and M. T. Oliveira J. Raman Spectrosc. 28, (1997), p 873. [3] J.-T. Han, Y.-H. Huang, X.-J. Wu, C.-L. Wu, W. Wei, B.o Peng, W. Huang and J. B. Goodenough Adv. Mater. 18 (2006), p. 2145, and the references therein.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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