Naslov
Phase relations in the Fe– Bi– O system under hydrothermal conditions

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

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

Izvornik
Conference proceedings EMC 2008 / - Berlin : Springer, 2008, 129-130

ISBN
978-3-540-85154-7

Skup
14th European Microscopy Congress EMC 2008

Mjesto i datum
Aachen, Njemačka, 01.-05.09.2008

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
hydrothermal synthesis ; bismuth ferrite ; hematite ; goethite ; bismuth oxide

Sažetak
The phases appearing during a hydrothermal reaction in the Fe– Bi– O system were investigated, with the aim to optimize the conditions for the syntheses of nanostructured bismuth ferrite. BiFeO3 is a multiferroic material ; hence it is ferroelectric and antiferromagnetic at room temperature [1]. 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 this linear effect is with thin-film epitaxial constraints. Thus, we expect the same effects in nanostructured BiFeO3. For the hydrothermal reactions two different precipitation procedures were carried out with various molar ratios (x) of iron and bismuth ions. In the first procedure the solutions containing both iron and bismuth ions (starting compounds Fe(NO3)3• 9H2O and Bi(NO3)3), were co-precipitated with tetraethyl ammonium hydroxide (TMAH), while in the second procedure the precipitation of the iron and bismuth ions was carried out separately, prior to mixing in the autoclave. Before the precipitation the Bi(NO3)3 was dissolved in HNO3 by vigorous stirring. The hydrothermal treatments were performed in the autoclave at pH 13.54 at 200°C for 6 h. The stability of the phases was checked in the case of 10 mol% Bi(NO3)3 by one week of hydrothermal treatment. The prepared phases were analyzed by X- ray powder diffraction (XRD), while the morphologies and nanostructure of the different phases were determined using high-resolution transmission electron microscopy (HRTEM) and/or scanning electron microscopy (SEM). The chemical compositions were examined by energy-dispersive X- ray analysis (EDXS). The phases observed in the prepared samples are listed in Table I. The tailoring of the goethite morphology in both series of precipitations was investigated by TEM. It was observed that the aspect ratio of goethite nanorods increased with the increase of Bi3+ ions in the reaction. However, other phases, like hematite and bismuth ferrite, were also produced. We obtained pure bismuth ferrite only in a co- precipitated sample with x=50%. In the case of separate precipitation, BiFeO3 was produced in a reaction with a lower content of Bi3+. Again, various phases coexisted in the sample. Goethite and hematite were shown to be stable phases (Figure 2). In hematite, containing approximately 7.2% of Bi3+, stacking faults were observed (Figure 2b). These are potential sites for Bi3+ accommodation, thus indicating a possible mechanism for the synthesis of nanosized BiFeO3.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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