Sonochemical Synthesis of Amorphous Yttrium Iron Oxides Embedded in Acetate Matrix and their Controlled Thermal Crystallization toward Garnet (Y3Fe5O12) and Perovskite (YFeO3) Nanostructures

Sonolysis of stoichiometric mixtures of tris(2,4-pentanedionato)iron, Fe(acac)(3), and tris(2,4-pentanedionato)yttrium, Y(acac)(3)(H2O)(3), under Ar atmosphere in tetraglyme led to a colloidal solution from which amorphous Y-Fe-O nanopowders could be precipitated by hexane. These powders are composed of amorphous nanoparticles (3 nm) of yttrium iron(III) oxide embedded in an acetate matrix as proved by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), mass spectrometry, and Mossbauer and IR spectroscopy. The increasing amount (0, 2, 6%) of added water in the reaction mixture was found to lower the organics content in the sonochemical products. The thermally induced crystallization of the amorphous Y-Fe-O nanoparticles was studied by thermal analysis (TG/DSC), evolved gas analysis (EGA), high-temperature XRD, and Mossbauer spectroscopy. Depending on the Y/Fe starting stoichiometric ratio in the sonicated reaction mixture, the single-phase YFeO3 (YIP) with the perovskite structure or Y3Fe5O12 (YIG) with the garnet structure can be synthesized by such controlled thermal transformation. The single-phase character of crystallized samples and the well-defined structure of both YIP and YIG nanoparticles were confirmed by XRD and Mossbauer spectra excluding the presence of any other phases in the reaction products. The hyperfine parameters of magnetically ordered spectrum of YIP reflect the octahedral environment of high-spin Fe(III) in the perovskite structure, while two nonequivalent octahedral and tetrahedral Fe(III) positions were identified in the YIG garnet spectrum.