Synthesis of Oriented BiFeO₃Thin Films by Chemical Solution Deposition: Phase, Texture, and Microstructural Development

Abstract

Textured, thin films of BiFeO3 (∼120 nm thickness) were synthesized by chemical solution deposition from a mixture of iron- and bismuth- 2-methoxyethoxides on Si(100)/SiO2/TiO2/Pt substrates. The use of alkoxides ensured good homogeneity and a low degree of organics that further facilitated low crystallization temperatures. Crystalline films were according to x-ray diffraction already obtained at 480 °C. Precursor characteristics were investigated using thermogravimetry and differential scanning calorimetry, whereas phase purity, microstructure and film topography were examined by x-ray diffraction, transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. A small (10%) Bi excess was found necessary to obtain dense, pore-free films. Such additions also prevented decomposition of BiFeO3 at high temperatures. The observed (012) texture is believed to originate from the growth mechanism as no relation to the substrate is found. This is also confirmed by observing (012) texture for films on glass substrates.

Effects of precursor chemistry and thermal treatment conditions on obtaining phase pure bismuth ferrite from aqueous gel precursors

“…The rhombohedral BiFeO 3 phase (JCPDS 86-1518, ICSD #82614) is observed, together with one diffraction peak of a secondary phase at 27.5 • 2θ (precursor a and b). This secondary phase is attributed to Bi 25 FeO 40 in literature, 4 presence of nitrate (precursor c) enhance the low temperature BiFeO 3 crystallization, demonstrated by the more pronounced diffraction peaks compared to precursor a. This is related to the high Bi ion mobility, which contributes to ion diffusion required for crystallization (precursor b), and to the self-heating effect in the nitrate containing precursor (c).…”

“…However, BiFeO 3 has for a long time been troubled by observations of phase impurities. This is related to the complex phase diagram of Bi 2 O 3 -Fe 2 O 3 , with Bi 2 Fe 4 O 9 and Bi 25 FeO 40 being the stable compounds surrounding BiFeO 3 , 4 and to Bi 2 O 3 loss during high temperature treatments for long periods. 5 Therefore, the low temperature crystallization which is in general enabled by sol(ution)-gel routes, due to the homogeneous mixing of metal ions on the atomic or molecular scale, shows great promise.…”

Low‐temperature preparation of bismuth ferrite microcrystals by a sol‐gel‐hydrothermal method

“…[4]. Therefore, it is very difficult to precisely control the optimizing conditions for obtaining a single phase multiferroic BiFeO 3 .…”

“…The main obstacle for BiFeO 3 applications is large leakage current because of the existence of the second phase. However, due to the complex phase diagram of Bi 2 O 3 -Fe 2 O 3 , with Bi 2 Fe 4 O 9 and Bi 25 FeO 40 being the stable compounds surrounding BiFeO 3 [4], and to Bi 2 O 3 loss during high temperature treatments for long periods, it is difficult to obtain a single phase BiFeO 3 without impurity through conventional solid-state reaction at a high sintering temperature [5]. So, in the solid-state route, nitric acid leaching is required to eliminate the impurity phases after the calcination of mixed bismuth and iron oxides [1], which resulted in coarser powders and the poor reproducibility.…”

Synthesis of multifunctional multiferroic materials from metalorganics

“…Tyholdt et al synthesized BiFeO 3 films by spin-coating a sol prepared by alcoholysis of Fe(O t Bu) 3 and Bi(O t Bu) 3 in 2-methoxyethanol [91]. Using sols with 0% and 10% Bi excess, films were deposited on Pt/TiO 2 /SiO 2 /Si(1 0 0) substrates.…”