Carboxylic acids and polyethylene glycol assisted synthesis of nanocrystalline nickel ferrites

Different synthesis methods for the preparation of nanocrystalline nickel ferrites are reported: the thermal decomposition of precursors, made of: (i) metal-nitrate salts with carboxylic acids (citric, malonic and tartaric), and (ii) metal-nitrate salts and polyethylene glycol (PEG), in the presence of potassium chloride as a capping agent. The as-prepared gel precursors were characterized by TGA/DTA, while the samples obtained after annealing at 450 °C were investigated by FTIR, FESEM, XRD and Mössbauer spectroscopy. Regardless of the type of carboxylic acid used, nanocrystallites prepared by (i) method are similar in size (11–16 nm), while the method (ii) gives crystallites ∼33 nm in size with negligible microstrain. The differences in the lattice parameter, ranging from 8.3369(2) to 8.3574(2) Å, result from cation distribution, nonstoichiometry and structural imperfections in the nickel ferrite nanoparticles. The Mössbauer spectra analysis indicates existence of large distortions of tetrahedral and octahedral sites in these spinel compounds.