Structural and magnetic properties of iron species/SiO ₂ nanocomposites obtained by sol‐gel methods

Abstract

The phase composition, local structure and magnetic interactions were investigated in Fe x O x -SiO 2 nanocomposites obtained by modern sol-gel methods. The very sensitive method of Mössbauer spectroscopy has evidenced the strong influence of the silica matrix precursor on the iron phase composition in the initial composites as well as on the size distribution of the hematite nanoparticles obtained by suitable thermal annealing treatments.

Iron(III) species dispersed in porous silica through sol–gel chemistry

“…The distribution of isomer shifts and quadrupole splittings results from the variety of local environments that the iron(III) ions experience in the amorphous xerogel. Both the average isomer shifts and quadrupole splittings are in complete agreement with those previously observed in iron(III) oxide doped aerogels and xerogels [40][41][42][43][44]. The appearance of broadened sextets below $30 K probably does not arise from ordered iron(III) oxides but rather from the onset, upon cooling, of slow paramagnetic relaxation [45,46] of the isolated iron(III) ions known to be present from UVvisible results and studies of magnetic properties, see below.…”

Iron oxide in a silica matrix prepared by the sol–gel method

“…Upon annealing at 550°C and at 1000°C these band characteristics for organic moieties bonded to the silica network vanish and the spectra of the resulted gels are quite similar. Some displacement of the main vibration band in the 1000-1200 cm − 1 range is noticed, that could be correlated to the disorder of the resulted inorganic structure due to its initial bonding to the organic radicals [30,31]. In the spectra of the samples annealed at 550°C and at 1000°C a new band appears at 590 cm − 1 which is even more evident at higher temperatures.…”

Investigations on sol–gel process and structural characterization of SiO2-P2O5 powders

“…Definite assignments and results have been obtained for the crystalline phases of the heat treated gel: Si 5 O(PO 4 ) 6 and Si(HPO 4 ) 2 ·H 2 O. The interpretation of the broad components rest much more complex, as motion at a molecular level is surely involved.…”

“…P_O double-bond and the high affinity of phosphorus for oxygen cause the protons in P\OH bonds to become strong hydrogen-bonding and easily adsorb the water molecules, which leads to a high proton conduction [1]. Compared with silica alone, phospho-silicates have higher proton conduction because the protons are more strongly bound to the non-bridging oxygen [2][3][4][5][6]. The benefit of incorporating zirconium phospho-silicates to NAFION™ membranes is seen by an increase in the conductivity for relative humidity >80% [7].…”