FTIR and Mossbauer Spectroscopy Investigations of Ag/FexAl2-xO3 Nanocomposites

An investigation of Ag/(hematite-alumina) solid solutions (Ag/FexAl2-xO3, 0.5 <= x <= 2) was completed via x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform Infrared spectroscopy (FTIR) and Mossbauer spectroscopy. Results reveal that the materials obtained by combustion synthesis are multi-phase nanocomposites and silver metal is supported on hematite-rich and alumina-rich nanoparticles for x < 2. For the iron-rich hematite phase, the experimental results indicated a beginning transition to the superparamagnetic state. They also show that the distribution of iron and aluminum cations in the product phases strongly depends on the starting concentrations and that their compositions closely correspond to those of the equilibrium phase diagram at about 1250 degrees C. Mossbauer signal intensities of samples with x = 0.5, 1.0 and 1.5 could consistently be explained by coexistence of phases of approximate composition Fe0.2Al1.8O3 and Fe1.8Al0.2O3 , which closely corresponds to the thermodynamic equilibrium phase diagram of Fe2O3-Al2O3 at about 1250 degrees C. Finally, the Mossbauer spectra reveal line shape changes for the samples with x < 2 which are characteristic for the onset of superparamagnetic behavior.