G. Piccaluga

IR and NMR study of nanoparticle-support interactions in a Fe2O3-SiO2 nanocomposite prepared by a sol-gel method

The interaction of iron oxide with the silica matrix in a Fe2O3-SiO2 nanocomposite prepared by a sol-gel method has been investigated using Near-, Mid-, and Far-IR, and 29Si MAS-, and 1H NMR techniques. Samples of nanocomposites and of pure silica obtained by the same preparation procedure and subjected to the same thermal treatments have been examined. Spectroscopic data indicate that the Fe2O3 nanoparticles interact with the silica or silanol groups at the surface of the cavities in which they form. This result allowed us to propose a model for the nanoparticle/silica interface.

X‐ray diffraction study of the average solute species in CaCl2 aqueous solutions

The structure of several CaCl2 aqueous solutions was studied by means of x‐ray diffraction. It is demonstrated that the solutions can be treated as being composed of independent hydrated ions, and for this reason the structural problem is limited to the study of close hydration. This description allows the calculation of structure functions in very good agreement with experimental data when using coordination number six and octahedral geometry for both the ionic species present.

Spin-glass-like freezing and enhanced magnetization in ultra-small CoFe2O4 nanoparticles

The magnetic properties of ultra-small (3 nm) CoFe(2)O(4) nanoparticles have been investigated by DC magnetization measurements as a function of temperature and magnetic field. The main features of the magnetic behaviour are blocking of non-interacting particle moments (zero-field-cooled magnetization T(max) approximately 40 K), a rapid increase of saturation magnetization (up to values higher than for the bulk material) at low T and an increase in anisotropy below 30 K due to the appearance of exchange bias. The low temperature behaviour is determined by a random freezing of surface spins. Localized spin-canting and cation distribution between the two sublattices of the spinel structure account quantitatively for the observed increase in saturation magnetization.

Cationic distribution and spin canting in CoFe2O4 nanoparticles

CoFe(2)O(4) nanoparticles (D(NPD) ~6 nm), prepared by a thermal decomposition technique, have been investigated through the combined use of dc magnetization measurements, neutron diffraction, and (57)Fe Mössbauer spectrometry under high applied magnetic field. Despite the small particle size, the value of saturation magnetization at 300 K (M(s) ͠= 70 A m(2) kg(-1)) and at 5 K (M(s) ͠= 100 A m(2) kg(-1)) are rather close to the bulk values, making the samples prepared with this method attractive for biomedical applications. Neutron diffraction measurements indicate the typical ferrimagnetic structure of the ferrites, showing an inversion degree (γ(NPD) = 0.74) that is in very good agreement with cationic distribution established from low temperature (10 K) Mössbauer measurements in high magnetic field (γ(moss) = 0.76). In addition, the in-field Mössbauer spectrum shows the presence of a non-collinear spin structure in both A and B sublattices. The results allow us to explain the high value of saturation magnetization and provide a better insight into the complex interplay between cationic distribution and magnetic disorder in ferrimagnetic nanoparticles.

Magnetic properties of cobalt ferrite-silica nanocomposites prepared by a sol-gel autocombustion technique

The magnetic properties of cobalt ferrite-silica nanocomposites with different concentrations (15, 30, and 50 wt %) and sizes (7, 16, and 28 nm) of ferrite particles have been studied by static magnetization measurements and Mossbauer spectroscopy. The results indicate a superparamagnetic behavior of the nanoparticles, with weak interactions slightly increasing with the cobalt ferrite content and with the particle size. From high-field Mossbauer spectra at low temperatures, the cationic distribution and the degree of spin canting have been estimated and both parameters are only slightly dependent on the particle size. The magnetic anisotropy constant increases with decreasing particle size, but in contrast to many other systems, the cobalt ferrite nanoparticles are found to have an anisotropy constant that is smaller than the bulk value. This can be explained by the distribution of the cations. The weak dependence of spin canting degree on particle size indicates that the spin canting is not simply a surface phenomenon but also occurs in the interiors of the particles.

Spin-Canting and Magnetic Anisotropy in Ultrasmall CoFe2O4 Nanoparticles

The magnetic properties of cobalt ferrite nanoparticles dispersed in a silica matrix in samples with different concentrations (5 and 10 wt% CoFe2O 4) and same particle size (3 nm) were studied by magnetization, DC and AC susceptibility, and Mossbauer spectroscopy measurements. The results indicate that the particles are very weakly interacting. The magnetic properties (saturation magnetization, anisotropy constant, and spin-canting) are discussed in relation to the cation distribution.

On the structure of methyl alcohol at room temperature

Methyl alcohol has been examined at room temperature by means of x‐ray diffraction technique. The radial distribution curve straightforwardly shows O ⋅⋅⋅ O interactions at about 2.8 A, which indicate that extensive hydrogen bonding is occurring in liquid methanol. The other prominent peaks of the radial curve fulfill the zig–zag chain model found in solid methanol. A direct analysis of the structure function leads to the conclusion that the average number of nearest oxygen neighbors per oxygen atom lies between 1.40 and 1.55. On the contrary, no unique conclusion, as far as the shape of the chain is concerned, can be obtained through the x‐ray scattering data.

Sol-gel formation of γ-Fe2O3/SiO2 nanocomposites

Abstract Fe 2 O 3 –SiO 2 nanocomposites with Fe/Si molar concentrations ranging between 0.25 and 0.57 were prepared by the sol-gel route. Tetraethoxysilane and iron(III) nitrate solution in ethanol were mixed and the hydrolysis reaction was promoted by the hydration water of the salt. The sols were gelated in air and then treated at 400°C for 4 h. The effect of the gelation process on the formation of the final nanocomposites has been investigated by studing different factors, such as temperature and surface of evaporation/volume ratio of the sol. Nanoparticles of γ and/or α iron oxide phase of different size were obtained in the silica matrix depending on the gelation conditions and on the later heat treatments. γ-Fe 2 O 3 –SiO 2 nanocomposites were obtained only when organic material was present into the pores of the gel silica matrix supporting their formation through a magnetite phase. At temperatures >400°C, the γ-phase begins to transform to the α-phase.

Structural properties of lead-iron phosphate glasses by X-ray diffraction☆

Abstract The structural properties of lead-iron phosphate glasses have been investigated by X-ray diffraction in an attempt to understand the chemical and mechanical characteristics presented by lead metaphosphate glass as the result of the addition of iron oxide. Information on FeO bond lengths and coordination numbers was obtained by a comparison of radial distribution functions of glass samples containing iron oxide and of the iron-free glass matrix. Stable structural arrangements around Fe(III) atoms were detected, which could be responsible for the stabilizing effect of Fe2O3 on lead metaphosphate glass.

Interactions and structure in aqueous NaNO3 solutions

Two concentrated (5 and 7 mol l−1) aqueous solutions of NaNO3 were investigated by x‐ray diffraction. The features of the total radial functions calculated from experimental intensity data show that the positional correlation is not very strong in the systems investigated. However, it is possible to account for experimental data only by using models in which hexahydrated Na+ ions have definite correlations with NO3− ions, even if not through formation of isolated ion pairs. The compatibility of our observations with spectroscopic results is also discussed.