Single-source-precursor synthesis of soft magnetic Fe3Si- and Fe5Si3-containing SiOC ceramic nanocomposites

We present here the single-source-precursor synthesis of Fe3Si and Fe5Si3-containing SiOC ceramic nanocomposites and investigation of their magnetic properties. The materials were prepared upon chemical modification of a hydroxy- and ethoxy-substituted polymethylsilsesquioxane with iron (III) acetylacetonate (Fe(acac)(3)) in different amounts (5, 15, 30 and 50 wt%), followed by cross-linking at 180 degrees C and pyrolysis in argon at temperatures ranging from 1000 degrees C to 1500 degrees C. The polymer-to-ceramic transformation of the iron-modified polysilsesquioxane and the evolution at high temperatures of the synthesized SiFeOC-based nanocomposite were studied by means of thermogravimetric analysis (TGA) coupled with evolved gas analysis (EGA) as well as X-ray diffraction (XRD). Upon pyrolysis at 1100 degrees C, the non-modified polysilsesquioxane converts into an amorphous SiOC ceramic; whereas the iron-modified precursors lead to Fe3Si/SiOC nanocomposites. Annealing of Fe3Si/SiOC at temperatures exceeding 1300 degrees C induced the crystallization of Fe5Si3 and beta-SiC. The crystallization of the different iron-containing phases at different temperatures is considered to be a consequence of the in situ generation of a Fe-C-Si alloy within the materials during pyrolysis. Depending on the Fe and Si content in the alloy, either Fe3Si and graphitic carbon (at 1000-1200 degrees C) or Fe5Si3 and beta-SiC (at T> 1300 degrees C) crystallize. All SiFeOC-based ceramic samples were found to exhibit soft magnetic properties. Magnetization versus applied field measurements of the samples show a saturation magnetization up to 26.0 emu/g, depending on the Fe content within the SiFeOC-based samples as well as on the crystalline iron silicide phases formed during pyrolysis. (C) 2013 Elsevier Ltd. All rights reserved.